This file describes gdb, the gnu symbolic debugger.
This is the Ninth Edition, for gdb Version 6.1.
Copyright (C) 1988-2004 Free Software Foundation, Inc.
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The purpose of a debugger such as gdb is to allow you to see what is going on “inside” another program while it executes—or what another program was doing at the moment it crashed.
gdb can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act:
You can use gdb to debug programs written in C and C++. For more information, see Supported languages. For more information, see C and C++.
Support for Modula-2 is partial. For information on Modula-2, see Modula-2.
Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. gdb does not support entering expressions, printing values, or similar features using Pascal syntax.
gdb can be used to debug programs written in Fortran, although it may be necessary to refer to some variables with a trailing underscore.
gdb can be used to debug programs written in Objective-C, using either the Apple/NeXT or the GNU Objective-C runtime.
gdb is free software, protected by the gnu General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program—but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms.
Fundamentally, the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else.
The biggest deficiency in the free software community today is not in the software—it is the lack of good free documentation that we can include with the free software. Many of our most important programs do not come with free reference manuals and free introductory texts. Documentation is an essential part of any software package; when an important free software package does not come with a free manual and a free tutorial, that is a major gap. We have many such gaps today.
Consider Perl, for instance. The tutorial manuals that people normally use are non-free. How did this come about? Because the authors of those manuals published them with restrictive terms—no copying, no modification, source files not available—which exclude them from the free software world.
That wasn't the first time this sort of thing happened, and it was far from the last. Many times we have heard a GNU user eagerly describe a manual that he is writing, his intended contribution to the community, only to learn that he had ruined everything by signing a publication contract to make it non-free.
Free documentation, like free software, is a matter of freedom, not price. The problem with the non-free manual is not that publishers charge a price for printed copies—that in itself is fine. (The Free Software Foundation sells printed copies of manuals, too.) The problem is the restrictions on the use of the manual. Free manuals are available in source code form, and give you permission to copy and modify. Non-free manuals do not allow this.
The criteria of freedom for a free manual are roughly the same as for free software. Redistribution (including the normal kinds of commercial redistribution) must be permitted, so that the manual can accompany every copy of the program, both on-line and on paper.
Permission for modification of the technical content is crucial too. When people modify the software, adding or changing features, if they are conscientious they will change the manual too—so they can provide accurate and clear documentation for the modified program. A manual that leaves you no choice but to write a new manual to document a changed version of the program is not really available to our community.
Some kinds of limits on the way modification is handled are acceptable. For example, requirements to preserve the original author's copyright notice, the distribution terms, or the list of authors, are ok. It is also no problem to require modified versions to include notice that they were modified. Even entire sections that may not be deleted or changed are acceptable, as long as they deal with nontechnical topics (like this one). These kinds of restrictions are acceptable because they don't obstruct the community's normal use of the manual.
However, it must be possible to modify all the technical content of the manual, and then distribute the result in all the usual media, through all the usual channels. Otherwise, the restrictions obstruct the use of the manual, it is not free, and we need another manual to replace it.
Please spread the word about this issue. Our community continues to lose manuals to proprietary publishing. If we spread the word that free software needs free reference manuals and free tutorials, perhaps the next person who wants to contribute by writing documentation will realize, before it is too late, that only free manuals contribute to the free software community.
If you are writing documentation, please insist on publishing it under the GNU Free Documentation License or another free documentation license. Remember that this decision requires your approval—you don't have to let the publisher decide. Some commercial publishers will use a free license if you insist, but they will not propose the option; it is up to you to raise the issue and say firmly that this is what you want. If the publisher you are dealing with refuses, please try other publishers. If you're not sure whether a proposed license is free, write to licensing@gnu.org.
You can encourage commercial publishers to sell more free, copylefted manuals and tutorials by buying them, and particularly by buying copies from the publishers that paid for their writing or for major improvements. Meanwhile, try to avoid buying non-free documentation at all. Check the distribution terms of a manual before you buy it, and insist that whoever seeks your business must respect your freedom. Check the history of the book, and try to reward the publishers that have paid or pay the authors to work on it.
The Free Software Foundation maintains a list of free documentation published by other publishers, at http://www.fsf.org/doc/other-free-books.html.
Richard Stallman was the original author of gdb, and of many other gnu programs. Many others have contributed to its development. This section attempts to credit major contributors. One of the virtues of free software is that everyone is free to contribute to it; with regret, we cannot actually acknowledge everyone here. The file ChangeLog in the gdb distribution approximates a blow-by-blow account.
Changes much prior to version 2.0 are lost in the mists of time.
Plea: Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names!
So that they may not regard their many labors as thankless, we particularly thank those who shepherded gdb through major releases: Andrew Cagney (releases 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0); Jim Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs (release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2, 3.1, and 3.0).
Richard Stallman, assisted at various times by Peter TerMaat, Chris Hanson, and Richard Mlynarik, handled releases through 2.8.
Michael Tiemann is the author of most of the gnu C++ support in gdb, with significant additional contributions from Per Bothner and Daniel Berlin. James Clark wrote the gnu C++ demangler. Early work on C++ was by Peter TerMaat (who also did much general update work leading to release 3.0).
gdb uses the BFD subroutine library to examine multiple object-file formats; BFD was a joint project of David V. Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
David Johnson wrote the original COFF support; Pace Willison did the original support for encapsulated COFF.
Brent Benson of Harris Computer Systems contributed DWARF 2 support.
Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete contributed Sun 386i support. Chris Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Jeff Law contributed HP PA and SOM support. Keith Packard contributed NS32K support. Doug Rabson contributed Acorn Risc Machine support. Bob Rusk contributed Harris Nighthawk CX-UX support. Chris Smith contributed Convex support (and Fortran debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed Symmetry support. Marko Mlinar contributed OpenRISC 1000 support.
Andreas Schwab contributed M68K gnu/Linux support.
Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries.
Jay Fenlason and Roland McGrath ensured that gdb and GAS agree about several machine instruction sets.
Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM contributed remote debugging modules for the i960, VxWorks, A29K UDI, and RDI targets, respectively.
Brian Fox is the author of the readline libraries providing command-line editing and command history.
Andrew Beers of SUNY Buffalo wrote the language-switching code, the Modula-2 support, and contributed the Languages chapter of this manual.
Fred Fish wrote most of the support for Unix System Vr4. He also enhanced the command-completion support to cover C++ overloaded symbols.
Hitachi America (now Renesas America), Ltd. sponsored the support for H8/300, H8/500, and Super-H processors.
NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D processors.
Toshiba sponsored the support for the TX39 Mips processor.
Matsushita sponsored the support for the MN10200 and MN10300 processors.
Fujitsu sponsored the support for SPARClite and FR30 processors.
Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware watchpoints.
Michael Snyder added support for tracepoints.
Stu Grossman wrote gdbserver.
Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly innumerable bug fixes and cleanups throughout gdb.
The following people at the Hewlett-Packard Company contributed support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0 (narrow mode), HP's implementation of kernel threads, HP's aC++ compiler, and the Text User Interface (nee Terminal User Interface): Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific information in this manual.
DJ Delorie ported gdb to MS-DOS, for the DJGPP project. Robert Hoehne made significant contributions to the DJGPP port.
Cygnus Solutions has sponsored gdb maintenance and much of its development since 1991. Cygnus engineers who have worked on gdb fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler, Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David Zuhn have made contributions both large and small.
Jim Blandy added support for preprocessor macros, while working for Red Hat.
You can use this manual at your leisure to read all about gdb. However, a handful of commands are enough to get started using the debugger. This chapter illustrates those commands.
One of the preliminary versions of gnu m4 (a generic macro
processor) exhibits the following bug: sometimes, when we change its
quote strings from the default, the commands used to capture one macro
definition within another stop working. In the following short m4
session, we define a macro foo which expands to 0000; we
then use the m4 built-in defn to define bar as the
same thing. However, when we change the open quote string to
<QUOTE> and the close quote string to <UNQUOTE>, the same
procedure fails to define a new synonym baz:
$ cd gnu/m4
$ ./m4
define(foo,0000)
foo
0000
define(bar,defn(`foo'))
bar
0000
changequote(<QUOTE>,<UNQUOTE>)
define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
C-d
m4: End of input: 0: fatal error: EOF in string
Let us use gdb to try to see what is going on.
$ gdb m4
gdb is free software and you are welcome to distribute copies
of it under certain conditions; type "show copying" to see
the conditions.
There is absolutely no warranty for gdb; type "show warranty"
for details.
gdb 6.1, Copyright 1999 Free Software Foundation, Inc...
(gdb)
gdb reads only enough symbol data to know where to find the rest when needed; as a result, the first prompt comes up very quickly. We now tell gdb to use a narrower display width than usual, so that examples fit in this manual.
(gdb) set width 70
We need to see how the m4 built-in changequote works.
Having looked at the source, we know the relevant subroutine is
m4_changequote, so we set a breakpoint there with the gdb
break command.
(gdb) break m4_changequote
Breakpoint 1 at 0x62f4: file builtin.c, line 879.
Using the run command, we start m4 running under gdb
control; as long as control does not reach the m4_changequote
subroutine, the program runs as usual:
(gdb) run
Starting program: /work/Editorial/gdb/gnu/m4/m4
define(foo,0000)
foo
0000
To trigger the breakpoint, we call changequote. gdb
suspends execution of m4, displaying information about the
context where it stops.
changequote(<QUOTE>,<UNQUOTE>)
Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
at builtin.c:879
879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
Now we use the command n (next) to advance execution to
the next line of the current function.
(gdb) n
882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
: nil,
set_quotes looks like a promising subroutine. We can go into it
by using the command s (step) instead of next.
step goes to the next line to be executed in any
subroutine, so it steps into set_quotes.
(gdb) s
set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
at input.c:530
530 if (lquote != def_lquote)
The display that shows the subroutine where m4 is now
suspended (and its arguments) is called a stack frame display. It
shows a summary of the stack. We can use the backtrace
command (which can also be spelled bt), to see where we are
in the stack as a whole: the backtrace command displays a
stack frame for each active subroutine.
(gdb) bt
#0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
at input.c:530
#1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
at builtin.c:882
#2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
#3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
at macro.c:71
#4 0x79dc in expand_input () at macro.c:40
#5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
We step through a few more lines to see what happens. The first two
times, we can use `s'; the next two times we use n to avoid
falling into the xstrdup subroutine.
(gdb) s
0x3b5c 532 if (rquote != def_rquote)
(gdb) s
0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
def_lquote : xstrdup(lq);
(gdb) n
536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
: xstrdup(rq);
(gdb) n
538 len_lquote = strlen(rquote);
The last line displayed looks a little odd; we can examine the variables
lquote and rquote to see if they are in fact the new left
and right quotes we specified. We use the command p
(print) to see their values.
(gdb) p lquote
$1 = 0x35d40 "<QUOTE>"
(gdb) p rquote
$2 = 0x35d50 "<UNQUOTE>"
lquote and rquote are indeed the new left and right quotes.
To look at some context, we can display ten lines of source
surrounding the current line with the l (list) command.
(gdb) l
533 xfree(rquote);
534
535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
: xstrdup (lq);
536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
: xstrdup (rq);
537
538 len_lquote = strlen(rquote);
539 len_rquote = strlen(lquote);
540 }
541
542 void
Let us step past the two lines that set len_lquote and
len_rquote, and then examine the values of those variables.
(gdb) n
539 len_rquote = strlen(lquote);
(gdb) n
540 }
(gdb) p len_lquote
$3 = 9
(gdb) p len_rquote
$4 = 7
That certainly looks wrong, assuming len_lquote and
len_rquote are meant to be the lengths of lquote and
rquote respectively. We can set them to better values using
the p command, since it can print the value of
any expression—and that expression can include subroutine calls and
assignments.
(gdb) p len_lquote=strlen(lquote)
$5 = 7
(gdb) p len_rquote=strlen(rquote)
$6 = 9
Is that enough to fix the problem of using the new quotes with the
m4 built-in defn? We can allow m4 to continue
executing with the c (continue) command, and then try the
example that caused trouble initially:
(gdb) c
Continuing.
define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
0000
Success! The new quotes now work just as well as the default ones. The
problem seems to have been just the two typos defining the wrong
lengths. We allow m4 exit by giving it an EOF as input:
C-d
Program exited normally.
The message `Program exited normally.' is from gdb; it
indicates m4 has finished executing. We can end our gdb
session with the gdb quit command.
(gdb) quit
This chapter discusses how to start gdb, and how to get out of it. The essentials are:
Invoke gdb by running the program gdb. Once started,
gdb reads commands from the terminal until you tell it to exit.
You can also run gdb with a variety of arguments and options,
to specify more of your debugging environment at the outset.
The command-line options described here are designed to cover a variety of situations; in some environments, some of these options may effectively be unavailable.
The most usual way to start gdb is with one argument, specifying an executable program:
gdb program
You can also start with both an executable program and a core file specified:
gdb program core
You can, instead, specify a process ID as a second argument, if you want to debug a running process:
gdb program 1234
would attach gdb to process 1234 (unless you also have a file
named 1234; gdb does check for a core file first).
Taking advantage of the second command-line argument requires a fairly complete operating system; when you use gdb as a remote debugger attached to a bare board, there may not be any notion of “process”, and there is often no way to get a core dump. gdb will warn you if it is unable to attach or to read core dumps.
You can optionally have gdb pass any arguments after the
executable file to the inferior using --args. This option stops
option processing.
gdb --args gcc -O2 -c foo.c
This will cause gdb to debug gcc, and to set
gcc's command-line arguments (see Arguments) to `-O2 -c foo.c'.
You can run gdb without printing the front material, which describes
gdb's non-warranty, by specifying -silent:
gdb -silent
You can further control how gdb starts up by using command-line options. gdb itself can remind you of the options available.
Type
gdb -help
to display all available options and briefly describe their use (`gdb -h' is a shorter equivalent).
All options and command line arguments you give are processed in sequential order. The order makes a difference when the `-x' option is used.
When gdb starts, it reads any arguments other than options as specifying an executable file and core file (or process ID). This is the same as if the arguments were specified by the `-se' and `-c' (or `-p' options respectively. (gdb reads the first argument that does not have an associated option flag as equivalent to the `-se' option followed by that argument; and the second argument that does not have an associated option flag, if any, as equivalent to the `-c'/`-p' option followed by that argument.) If the second argument begins with a decimal digit, gdb will first attempt to attach to it as a process, and if that fails, attempt to open it as a corefile. If you have a corefile whose name begins with a digit, you can prevent gdb from treating it as a pid by prefixing it with ./, eg. ./12345.
If gdb has not been configured to included core file support, such as for most embedded targets, then it will complain about a second argument and ignore it.
Many options have both long and short forms; both are shown in the following list. gdb also recognizes the long forms if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with `--' rather than `-', though we illustrate the more usual convention.)
-symbols file-s file-exec file-e file-se file-core file-c file-c number-pid number-p numberattach command.
If there is no such process, gdb will attempt to open a core
file named number.
-command file-x file-directory directory-d directory-m-mappedmmap
system call, you can use this option
to have gdb write the symbols from your
program into a reusable file in the current directory. If the program you are debugging is
called /tmp/fred, the mapped symbol file is /tmp/fred.syms.
Future gdb debugging sessions notice the presence of this file,
and can quickly map in symbol information from it, rather than reading
the symbol table from the executable program.
The .syms file is specific to the host machine where gdb
is run. It holds an exact image of the internal gdb symbol
table. It cannot be shared across multiple host platforms.
-r-readnowYou typically combine the -mapped and -readnow options in
order to build a .syms file that contains complete symbol
information. (See Commands to specify files, for information
on .syms files.) A simple gdb invocation to do nothing
but build a .syms file for future use is:
gdb -batch -nx -mapped -readnow programname
You can run gdb in various alternative modes—for example, in batch mode or quiet mode.
-nx-n-quiet-silent-q-batch0 after processing all the
command files specified with `-x' (and all commands from
initialization files, if not inhibited with `-n'). Exit with
nonzero status if an error occurs in executing the gdb commands
in the command files.
Batch mode may be useful for running gdb as a filter, for example to download and run a program on another computer; in order to make this more useful, the message
Program exited normally.
(which is ordinarily issued whenever a program running under
gdb control terminates) is not issued when running in batch
mode.
-nowindows-nw-windows-w-cd directory-fullname-f-epoch-annotate levelThe annotation mechanism has largely been superseeded by gdb/mi
(see GDB/MI).
-asyncWhen the standard input is connected to a terminal device, gdb
uses the asynchronous event loop by default, unless disabled by the
`-noasync' option.
-noasync--args-baud bps-b bps-tty device-t device-tui-interpreter interp`--interpreter=mi' (or `--interpreter=mi2') causes
gdb to use the gdb/mi interface (see The gdb/mi Interface) included since GDBN version 6.0. The
previous gdb/mi interface, included in gdb version 5.3 and
selected with `--interpreter=mi1', is deprecated. Earlier
gdb/mi interfaces are no longer supported.
-write-statistics-versionquit [expression]qquit command (abbreviated
q), or type an end-of-file character (usually C-d). If you
do not supply expression, gdb will terminate normally;
otherwise it will terminate using the result of expression as the
error code.
An interrupt (often C-c) does not exit from gdb, but rather terminates the action of any gdb command that is in progress and returns to gdb command level. It is safe to type the interrupt character at any time because gdb does not allow it to take effect until a time when it is safe.
If you have been using gdb to control an attached process or
device, you can release it with the detach command
(see Debugging an already-running process).
If you need to execute occasional shell commands during your
debugging session, there is no need to leave or suspend gdb; you can
just use the shell command.
shell command stringSHELL determines which
shell to run. Otherwise gdb uses the default shell
(/bin/sh on Unix systems, COMMAND.COM on MS-DOS, etc.).
The utility make is often needed in development environments.
You do not have to use the shell command for this purpose in
gdb:
make make-argsmake program with the specified
arguments. This is equivalent to `shell make make-args'.
You may want to save the output of gdb commands to a file. There are several commands to control gdb's logging.
set logging onset logging offset logging file fileset logging overwrite [on|off]overwrite if
you want set logging on to overwrite the logfile instead.
set logging redirect [on|off]redirect if you want output to go only to the log file.
show loggingYou can abbreviate a gdb command to the first few letters of the command name, if that abbreviation is unambiguous; and you can repeat certain gdb commands by typing just <RET>. You can also use the <TAB> key to get gdb to fill out the rest of a word in a command (or to show you the alternatives available, if there is more than one possibility).
A gdb command is a single line of input. There is no limit on
how long it can be. It starts with a command name, which is followed by
arguments whose meaning depends on the command name. For example, the
command step accepts an argument which is the number of times to
step, as in `step 5'. You can also use the step command
with no arguments. Some commands do not allow any arguments.
gdb command names may always be truncated if that abbreviation is
unambiguous. Other possible command abbreviations are listed in the
documentation for individual commands. In some cases, even ambiguous
abbreviations are allowed; for example, s is specially defined as
equivalent to step even though there are other commands whose
names start with s. You can test abbreviations by using them as
arguments to the help command.
A blank line as input to gdb (typing just <RET>) means to
repeat the previous command. Certain commands (for example, run)
will not repeat this way; these are commands whose unintentional
repetition might cause trouble and which you are unlikely to want to
repeat.
The list and x commands, when you repeat them with
<RET>, construct new arguments rather than repeating
exactly as typed. This permits easy scanning of source or memory.
gdb can also use <RET> in another way: to partition lengthy
output, in a way similar to the common utility more
(see Screen size). Since it is easy to press one
<RET> too many in this situation, gdb disables command
repetition after any command that generates this sort of display.
Any text from a # to the end of the line is a comment; it does nothing. This is useful mainly in command files (see Command files).
The C-o binding is useful for repeating a complex sequence of commands. This command accepts the current line, like RET, and then fetches the next line relative to the current line from the history for editing.
gdb can fill in the rest of a word in a command for you, if there is only one possibility; it can also show you what the valid possibilities are for the next word in a command, at any time. This works for gdb commands, gdb subcommands, and the names of symbols in your program.
Press the <TAB> key whenever you want gdb to fill out the rest of a word. If there is only one possibility, gdb fills in the word, and waits for you to finish the command (or press <RET> to enter it). For example, if you type
(gdb) info bre <TAB>
gdb fills in the rest of the word `breakpoints', since that is
the only info subcommand beginning with `bre':
(gdb) info breakpoints
You can either press <RET> at this point, to run the info
breakpoints command, or backspace and enter something else, if
`breakpoints' does not look like the command you expected. (If you
were sure you wanted info breakpoints in the first place, you
might as well just type <RET> immediately after `info bre',
to exploit command abbreviations rather than command completion).
If there is more than one possibility for the next word when you press <TAB>, gdb sounds a bell. You can either supply more characters and try again, or just press <TAB> a second time; gdb displays all the possible completions for that word. For example, you might want to set a breakpoint on a subroutine whose name begins with `make_', but when you type b make_<TAB> gdb just sounds the bell. Typing <TAB> again displays all the function names in your program that begin with those characters, for example:
(gdb) b make_ <TAB>
gdb sounds bell; press <TAB> again, to see:
make_a_section_from_file make_environ make_abs_section make_function_type make_blockvector make_pointer_type make_cleanup make_reference_type make_command make_symbol_completion_list (gdb) b make_
After displaying the available possibilities, gdb copies your partial input (`b make_' in the example) so you can finish the command.
If you just want to see the list of alternatives in the first place, you can press M-? rather than pressing <TAB> twice. M-? means <META> ?. You can type this either by holding down a key designated as the <META> shift on your keyboard (if there is one) while typing ?, or as <ESC> followed by ?.
Sometimes the string you need, while logically a “word”, may contain
parentheses or other characters that gdb normally excludes from
its notion of a word. To permit word completion to work in this
situation, you may enclose words in ' (single quote marks) in
gdb commands.
The most likely situation where you might need this is in typing the
name of a C++ function. This is because C++ allows function
overloading (multiple definitions of the same function, distinguished
by argument type). For example, when you want to set a breakpoint you
may need to distinguish whether you mean the version of name
that takes an int parameter, name(int), or the version
that takes a float parameter, name(float). To use the
word-completion facilities in this situation, type a single quote
' at the beginning of the function name. This alerts
gdb that it may need to consider more information than usual
when you press <TAB> or M-? to request word completion:
(gdb) b 'bubble( M-?
bubble(double,double) bubble(int,int)
(gdb) b 'bubble(
In some cases, gdb can tell that completing a name requires using quotes. When this happens, gdb inserts the quote for you (while completing as much as it can) if you do not type the quote in the first place:
(gdb) b bub <TAB>
gdb alters your input line to the following, and rings a bell:
(gdb) b 'bubble(
In general, gdb can tell that a quote is needed (and inserts it) if you have not yet started typing the argument list when you ask for completion on an overloaded symbol.
For more information about overloaded functions, see C++ expressions. You can use the command set
overload-resolution off to disable overload resolution;
see gdb features for C++.
You can always ask gdb itself for information on its commands,
using the command help.
helphhelp (abbreviated h) with no arguments to
display a short list of named classes of commands:
(gdb) help
List of classes of commands:
aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without
stopping the program
user-defined -- User-defined commands
Type "help" followed by a class name for a list of
commands in that class.
Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)
help classstatus:
(gdb) help status
Status inquiries.
List of commands:
info -- Generic command for showing things
about the program being debugged
show -- Generic command for showing things
about the debugger
Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)
help commandhelp argument, gdb displays a
short paragraph on how to use that command.
apropos argsapropos args command searches through all of the gdb
commands, and their documentation, for the regular expression specified in
args. It prints out all matches found. For example:
apropos reload
results in:
set symbol-reloading -- Set dynamic symbol table reloading
multiple times in one run
show symbol-reloading -- Show dynamic symbol table reloading
multiple times in one run
complete argscomplete args command lists all the possible completions
for the beginning of a command. Use args to specify the beginning of the
command you want completed. For example:
complete i
results in:
if
ignore
info
inspect
This is intended for use by gnu Emacs.
In addition to help, you can use the gdb commands info
and show to inquire about the state of your program, or the state
of gdb itself. Each command supports many topics of inquiry; this
manual introduces each of them in the appropriate context. The listings
under info and under show in the Index point to
all the sub-commands. See Index.
infoi) is for describing the state of your
program. For example, you can list the arguments given to your program
with info args, list the registers currently in use with info
registers, or list the breakpoints you have set with info breakpoints.
You can get a complete list of the info sub-commands with
help info.
setset. For example, you can set the gdb prompt to a $-sign with
set prompt $.
showinfo, show is for describing the state of
gdb itself.
You can change most of the things you can show, by using the
related command set; for example, you can control what number
system is used for displays with set radix, or simply inquire
which is currently in use with show radix.
To display all the settable parameters and their current
values, you can use show with no arguments; you may also use
info set. Both commands produce the same display.
Here are three miscellaneous show subcommands, all of which are
exceptional in lacking corresponding set commands:
show versionshow copyingshow warrantyWhen you run a program under gdb, you must first generate debugging information when you compile it.
You may start gdb with its arguments, if any, in an environment of your choice. If you are doing native debugging, you may redirect your program's input and output, debug an already running process, or kill a child process.
In order to debug a program effectively, you need to generate debugging information when you compile it. This debugging information is stored in the object file; it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code.
To request debugging information, specify the `-g' option when you run the compiler.
Most compilers do not include information about preprocessor macros in the debugging information if you specify the -g flag alone, because this information is rather large. Version 3.1 of gcc, the gnu C compiler, provides macro information if you specify the options -gdwarf-2 and -g3; the former option requests debugging information in the Dwarf 2 format, and the latter requests “extra information”. In the future, we hope to find more compact ways to represent macro information, so that it can be included with -g alone.
Many C compilers are unable to handle the `-g' and `-O' options together. Using those compilers, you cannot generate optimized executables containing debugging information.
gcc, the gnu C compiler, supports `-g' with or without `-O', making it possible to debug optimized code. We recommend that you always use `-g' whenever you compile a program. You may think your program is correct, but there is no sense in pushing your luck.
When you debug a program compiled with `-g -O', remember that the optimizer is rearranging your code; the debugger shows you what is really there. Do not be too surprised when the execution path does not exactly match your source file! An extreme example: if you define a variable, but never use it, gdb never sees that variable—because the compiler optimizes it out of existence.
Some things do not work as well with `-g -O' as with just `-g', particularly on machines with instruction scheduling. If in doubt, recompile with `-g' alone, and if this fixes the problem, please report it to us as a bug (including a test case!).
Older versions of the gnu C compiler permitted a variant option `-gg' for debugging information. gdb no longer supports this format; if your gnu C compiler has this option, do not use it.
runrrun command to start your program under gdb.
You must first specify the program name (except on VxWorks) with an
argument to gdb (see Getting In and Out of gdb), or by using the file or exec-file command
(see Commands to specify files).
If you are running your program in an execution environment that
supports processes, run creates an inferior process and makes
that process run your program. (In environments without processes,
run jumps to the start of your program.)
The execution of a program is affected by certain information it receives from its superior. gdb provides ways to specify this information, which you must do before starting your program. (You can change it after starting your program, but such changes only affect your program the next time you start it.) This information may be divided into four categories:
run command. If a shell is available on your target, the shell
is used to pass the arguments, so that you may use normal conventions
(such as wildcard expansion or variable substitution) in describing
the arguments.
In Unix systems, you can control which shell is used with the
SHELL environment variable.
See Your program's arguments.
set environment and unset
environment to change parts of the environment that affect
your program. See Your program's environment.
cd command in gdb.
See Your program's working directory.
run command line, or you can use the tty command to
set a different device for your program.
See Your program's input and output.
Warning: While input and output redirection work, you cannot use pipes to pass the output of the program you are debugging to another program; if you attempt this, gdb is likely to wind up debugging the wrong program.
When you issue the run command, your program begins to execute
immediately. See Stopping and continuing, for discussion
of how to arrange for your program to stop. Once your program has
stopped, you may call functions in your program, using the print
or call commands. See Examining Data.
If the modification time of your symbol file has changed since the last time gdb read its symbols, gdb discards its symbol table, and reads it again. When it does this, gdb tries to retain your current breakpoints.
The arguments to your program can be specified by the arguments of the
run command.
They are passed to a shell, which expands wildcard characters and
performs redirection of I/O, and thence to your program. Your
SHELL environment variable (if it exists) specifies what shell
gdb uses. If you do not define SHELL, gdb uses
the default shell (/bin/sh on Unix).
On non-Unix systems, the program is usually invoked directly by gdb, which emulates I/O redirection via the appropriate system calls, and the wildcard characters are expanded by the startup code of the program, not by the shell.
run with no arguments uses the same arguments used by the previous
run, or those set by the set args command.
set argsset args has no arguments, run executes your program
with no arguments. Once you have run your program with arguments,
using set args before the next run is the only way to run
it again without arguments.
show argsThe environment consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running your program with a modified environment without having to start gdb over again.
path directoryPATH environment variable
(the search path for executables) that will be passed to your program.
The value of PATH used by gdb does not change.
You may specify several directory names, separated by whitespace or by a
system-dependent separator character (`:' on Unix, `;' on
MS-DOS and MS-Windows). If directory is already in the path, it
is moved to the front, so it is searched sooner.
You can use the string `$cwd' to refer to whatever is the current
working directory at the time gdb searches the path. If you
use `.' instead, it refers to the directory where you executed the
path command. gdb replaces `.' in the
directory argument (with the current path) before adding
directory to the search path.
show pathsPATH
environment variable).
show environment [varname]environment as env.
set environment varname [=value]For example, this command:
set env USER = foo
tells the debugged program, when subsequently run, that its user is named `foo'. (The spaces around `=' are used for clarity here; they are not actually required.)
unset environment varnameunset environment removes the variable from the environment,
rather than assigning it an empty value.
Warning: On Unix systems, gdb runs your program using
the shell indicated
by your SHELL environment variable if it exists (or
/bin/sh if not). If your SHELL variable names a shell
that runs an initialization file—such as .cshrc for C-shell, or
.bashrc for BASH—any variables you set in that file affect
your program. You may wish to move setting of environment variables to
files that are only run when you sign on, such as .login or
.profile.
Each time you start your program with run, it inherits its
working directory from the current working directory of gdb.
The gdb working directory is initially whatever it inherited
from its parent process (typically the shell), but you can specify a new
working directory in gdb with the cd command.
The gdb working directory also serves as a default for the commands that specify files for gdb to operate on. See Commands to specify files.
By default, the program you run under gdb does input and output to the same terminal that gdb uses. gdb switches the terminal to its own terminal modes to interact with you, but it records the terminal modes your program was using and switches back to them when you continue running your program.
info terminalYou can redirect your program's input and/or output using shell
redirection with the run command. For example,
run > outfile
starts your program, diverting its output to the file outfile.
Another way to specify where your program should do input and output is
with the tty command. This command accepts a file name as
argument, and causes this file to be the default for future run
commands. It also resets the controlling terminal for the child
process, for future run commands. For example,
tty /dev/ttyb
directs that processes started with subsequent run commands
default to do input and output on the terminal /dev/ttyb and have
that as their controlling terminal.
An explicit redirection in run overrides the tty command's
effect on the input/output device, but not its effect on the controlling
terminal.
When you use the tty command or redirect input in the run
command, only the input for your program is affected. The input
for gdb still comes from your terminal.
attach process-idinfo files shows your active
targets.) The command takes as argument a process ID. The usual way to
find out the process-id of a Unix process is with the ps utility,
or with the `jobs -l' shell command.
attach does not repeat if you press <RET> a second time after
executing the command.
To use attach, your program must be running in an environment
which supports processes; for example, attach does not work for
programs on bare-board targets that lack an operating system. You must
also have permission to send the process a signal.
When you use attach, the debugger finds the program running in
the process first by looking in the current working directory, then (if
the program is not found) by using the source file search path
(see Specifying source directories). You can also use
the file command to load the program. See Commands to Specify Files.
The first thing gdb does after arranging to debug the specified
process is to stop it. You can examine and modify an attached process
with all the gdb commands that are ordinarily available when
you start processes with run. You can insert breakpoints; you
can step and continue; you can modify storage. If you would rather the
process continue running, you may use the continue command after
attaching gdb to the process.
detachdetach command to release it from gdb control. Detaching
the process continues its execution. After the detach command,
that process and gdb become completely independent once more, and you
are ready to attach another process or start one with run.
detach does not repeat if you press <RET> again after
executing the command.
If you exit gdb or use the run command while you have an
attached process, you kill that process. By default, gdb asks
for confirmation if you try to do either of these things; you can
control whether or not you need to confirm by using the set
confirm command (see Optional warnings and messages).
killThis command is useful if you wish to debug a core dump instead of a running process. gdb ignores any core dump file while your program is running.
On some operating systems, a program cannot be executed outside gdb
while you have breakpoints set on it inside gdb. You can use the
kill command in this situation to permit running your program
outside the debugger.
The kill command is also useful if you wish to recompile and
relink your program, since on many systems it is impossible to modify an
executable file while it is running in a process. In this case, when you
next type run, gdb notices that the file has changed, and
reads the symbol table again (while trying to preserve your current
breakpoint settings).
In some operating systems, such as HP-UX and Solaris, a single program may have more than one thread of execution. The precise semantics of threads differ from one operating system to another, but in general the threads of a single program are akin to multiple processes—except that they share one address space (that is, they can all examine and modify the same variables). On the other hand, each thread has its own registers and execution stack, and perhaps private memory.
gdb provides these facilities for debugging multi-thread programs:
Warning: These facilities are not yet available on every gdb configuration where the operating system supports threads. If your gdb does not support threads, these commands have no effect. For example, a system without thread support shows no output from `info threads', and always rejects thethreadcommand, like this:(gdb) info threads (gdb) thread 1 Thread ID 1 not known. Use the "info threads" command to see the IDs of currently known threads.
The gdb thread debugging facility allows you to observe all threads while your program runs—but whenever gdb takes control, one thread in particular is always the focus of debugging. This thread is called the current thread. Debugging commands show program information from the perspective of the current thread.
Whenever gdb detects a new thread in your program, it displays the target system's identification for the thread with a message in the form `[New systag]'. systag is a thread identifier whose form varies depending on the particular system. For example, on LynxOS, you might see
[New process 35 thread 27]
when gdb notices a new thread. In contrast, on an SGI system, the systag is simply something like `process 368', with no further qualifier.
For debugging purposes, gdb associates its own thread number—always a single integer—with each thread in your program.
info threadsAn asterisk `*' to the left of the gdb thread number indicates the current thread.
For example,
(gdb) info threads
3 process 35 thread 27 0x34e5 in sigpause ()
2 process 35 thread 23 0x34e5 in sigpause ()
* 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
at threadtest.c:68
On HP-UX systems:
For debugging purposes, gdb associates its own thread number—a small integer assigned in thread-creation order—with each thread in your program.
Whenever gdb detects a new thread in your program, it displays both gdb's thread number and the target system's identification for the thread with a message in the form `[New systag]'. systag is a thread identifier whose form varies depending on the particular system. For example, on HP-UX, you see
[New thread 2 (system thread 26594)]
when gdb notices a new thread.
info threadsAn asterisk `*' to the left of the gdb thread number indicates the current thread.
For example,
(gdb) info threads
* 3 system thread 26607 worker (wptr=0x7b09c318 "@") \
at quicksort.c:137
2 system thread 26606 0x7b0030d8 in __ksleep () \
from /usr/lib/libc.2
1 system thread 27905 0x7b003498 in _brk () \
from /usr/lib/libc.2
thread threadno
(gdb) thread 2
[Switching to process 35 thread 23]
0x34e5 in sigpause ()
As with the `[New ...]' message, the form of the text after `Switching to' depends on your system's conventions for identifying threads.
thread apply [threadno] [all] argsthread apply command allows you to apply a command to one or
more threads. Specify the numbers of the threads that you want affected
with the command argument threadno. threadno is the internal
gdb thread number, as shown in the first field of the `info
threads' display. To apply a command to all threads, use
thread apply all args.
Whenever gdb stops your program, due to a breakpoint or a signal, it automatically selects the thread where that breakpoint or signal happened. gdb alerts you to the context switch with a message of the form `[Switching to systag]' to identify the thread.
See Stopping and starting multi-thread programs, for more information about how gdb behaves when you stop and start programs with multiple threads.
See Setting watchpoints, for information about watchpoints in programs with multiple threads.
On most systems, gdb has no special support for debugging
programs which create additional processes using the fork
function. When a program forks, gdb will continue to debug the
parent process and the child process will run unimpeded. If you have
set a breakpoint in any code which the child then executes, the child
will get a SIGTRAP signal which (unless it catches the signal)
will cause it to terminate.
However, if you want to debug the child process there is a workaround
which isn't too painful. Put a call to sleep in the code which
the child process executes after the fork. It may be useful to sleep
only if a certain environment variable is set, or a certain file exists,
so that the delay need not occur when you don't want to run gdb
on the child. While the child is sleeping, use the ps program to
get its process ID. Then tell gdb (a new invocation of
gdb if you are also debugging the parent process) to attach to
the child process (see Attach). From that point on you can debug
the child process just like any other process which you attached to.
On some systems, gdb provides support for debugging programs that
create additional processes using the fork or vfork functions.
Currently, the only platforms with this feature are HP-UX (11.x and later
only?) and GNU/Linux (kernel version 2.5.60 and later).
By default, when a program forks, gdb will continue to debug the parent process and the child process will run unimpeded.
If you want to follow the child process instead of the parent process,
use the command set follow-fork-mode.
set follow-fork-mode modefork or
vfork. A call to fork or vfork creates a new
process. The mode can be:
parentchildshow follow-fork-modefork or vfork call.
If you ask to debug a child process and a vfork is followed by an
exec, gdb executes the new target up to the first
breakpoint in the new target. If you have a breakpoint set on
main in your original program, the breakpoint will also be set on
the child process's main.
When a child process is spawned by vfork, you cannot debug the
child or parent until an exec call completes.
If you issue a run command to gdb after an exec
call executes, the new target restarts. To restart the parent process,
use the file command with the parent executable name as its
argument.
You can use the catch command to make gdb stop whenever
a fork, vfork, or exec call is made. See Setting catchpoints.
The principal purposes of using a debugger are so that you can stop your program before it terminates; or so that, if your program runs into trouble, you can investigate and find out why.
Inside gdb, your program may stop for any of several reasons,
such as a signal, a breakpoint, or reaching a new line after a
gdb command such as step. You may then examine and
change variables, set new breakpoints or remove old ones, and then
continue execution. Usually, the messages shown by gdb provide
ample explanation of the status of your program—but you can also
explicitly request this information at any time.
info programA breakpoint makes your program stop whenever a certain point in
the program is reached. For each breakpoint, you can add conditions to
control in finer detail whether your program stops. You can set
breakpoints with the break command and its variants (see Setting breakpoints), to specify the place where your program
should stop by line number, function name or exact address in the
program.
In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
breakpoints in shared libraries before the executable is run. There is
a minor limitation on HP-UX systems: you must wait until the executable
is run in order to set breakpoints in shared library routines that are
not called directly by the program (for example, routines that are
arguments in a pthread_create call).
A watchpoint is a special breakpoint that stops your program when the value of an expression changes. You must use a different command to set watchpoints (see Setting watchpoints), but aside from that, you can manage a watchpoint like any other breakpoint: you enable, disable, and delete both breakpoints and watchpoints using the same commands.
You can arrange to have values from your program displayed automatically whenever gdb stops at a breakpoint. See Automatic display.
A catchpoint is another special breakpoint that stops your program
when a certain kind of event occurs, such as the throwing of a C++
exception or the loading of a library. As with watchpoints, you use a
different command to set a catchpoint (see Setting catchpoints), but aside from that, you can manage a catchpoint like any
other breakpoint. (To stop when your program receives a signal, use the
handle command; see Signals.)
gdb assigns a number to each breakpoint, watchpoint, or catchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be enabled or disabled; if disabled, it has no effect on your program until you enable it again.
Some gdb commands accept a range of breakpoints on which to operate. A breakpoint range is either a single breakpoint number, like `5', or two such numbers, in increasing order, separated by a hyphen, like `5-7'. When a breakpoint range is given to a command, all breakpoint in that range are operated on.
Breakpoints are set with the break command (abbreviated
b). The debugger convenience variable `$bpnum' records the
number of the breakpoint you've set most recently; see Convenience variables, for a discussion of what you can do with
convenience variables.
You have several ways to say where the breakpoint should go.
break functionbreak +offsetbreak -offsetbreak linenumbreak filename:linenumbreak filename:functionbreak *addressbreakbreak sets a breakpoint at
the next instruction to be executed in the selected stack frame
(see Examining the Stack). In any selected frame but the
innermost, this makes your program stop as soon as control
returns to that frame. This is similar to the effect of a
finish command in the frame inside the selected frame—except
that finish does not leave an active breakpoint. If you use
break without an argument in the innermost frame, gdb stops
the next time it reaches the current location; this may be useful
inside loops.
gdb normally ignores breakpoints when it resumes execution, until at
least one instruction has been executed. If it did not do this, you
would be unable to proceed past a breakpoint without first disabling the
breakpoint. This rule applies whether or not the breakpoint already
existed when your program stopped.
break ... if condtbreak argsbreak command, and the breakpoint is set in the same
way, but the breakpoint is automatically deleted after the first time your
program stops there. See Disabling breakpoints.
hbreak argsbreak command and the breakpoint is set in the same way, but the
breakpoint requires hardware support and some target hardware may not
have this support. The main purpose of this is EPROM/ROM code
debugging, so you can set a breakpoint at an instruction without
changing the instruction. This can be used with the new trap-generation
provided by SPARClite DSU and some x86-based targets. These targets
will generate traps when a program accesses some data or instruction
address that is assigned to the debug registers. However the hardware
breakpoint registers can take a limited number of breakpoints. For
example, on the DSU, only two data breakpoints can be set at a time, and
gdb will reject this command if more than two are used. Delete
or disable unused hardware breakpoints before setting new ones
(see Disabling). See Break conditions.
See set remote hardware-breakpoint-limit.
thbreak argshbreak command and the breakpoint is set in
the same way. However, like the tbreak command,
the breakpoint is automatically deleted after the
first time your program stops there. Also, like the hbreak
command, the breakpoint requires hardware support and some target hardware
may not have this support. See Disabling breakpoints.
See also Break conditions.
rbreak regexbreak command. You can delete them, disable them, or make
them conditional the same way as any other breakpoint.
The syntax of the regular expression is the standard one used with tools
like grep. Note that this is different from the syntax used by
shells, so for instance foo* matches all functions that include
an fo followed by zero or more os. There is an implicit
.* leading and trailing the regular expression you supply, so to
match only functions that begin with foo, use ^foo.
When debugging C++ programs, rbreak is useful for setting
breakpoints on overloaded functions that are not members of any special
classes.
info breakpoints [n]info break [n]info watchpoints [n]If a breakpoint is conditional, info break shows the condition on
the line following the affected breakpoint; breakpoint commands, if any,
are listed after that. A pending breakpoint is allowed to have a condition
specified for it. The condition is not parsed for validity until a shared
library is loaded that allows the pending breakpoint to resolve to a
valid location.
info break with a breakpoint
number n as argument lists only that breakpoint. The
convenience variable $_ and the default examining-address for
the x command are set to the address of the last breakpoint
listed (see Examining memory).
info break displays a count of the number of times the breakpoint
has been hit. This is especially useful in conjunction with the
ignore command. You can ignore a large number of breakpoint
hits, look at the breakpoint info to see how many times the breakpoint
was hit, and then run again, ignoring one less than that number. This
will get you quickly to the last hit of that breakpoint.
gdb allows you to set any number of breakpoints at the same place in your program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (see Break conditions).
If a specified breakpoint location cannot be found, it may be due to the fact that the location is in a shared library that is yet to be loaded. In such a case, you may want gdb to create a special breakpoint (known as a pending breakpoint) that attempts to resolve itself in the future when an appropriate shared library gets loaded.
Pending breakpoints are useful to set at the start of your gdb session for locations that you know will be dynamically loaded later by the program being debugged. When shared libraries are loaded, a check is made to see if the load resolves any pending breakpoint locations. If a pending breakpoint location gets resolved, a regular breakpoint is created and the original pending breakpoint is removed.
gdb provides some additional commands for controlling pending breakpoint support:
set breakpoint pending autoset breakpoint pending onset breakpoint pending offshow breakpoint pendingNormal breakpoint operations apply to pending breakpoints as well. You may specify a condition for a pending breakpoint and/or commands to run when the breakpoint is reached. You can also enable or disable the pending breakpoint. When you specify a condition for a pending breakpoint, the parsing of the condition will be deferred until the point where the pending breakpoint location is resolved. Disabling a pending breakpoint tells gdb to not attempt to resolve the breakpoint on any subsequent shared library load. When a pending breakpoint is re-enabled, gdb checks to see if the location is already resolved. This is done because any number of shared library loads could have occurred since the time the breakpoint was disabled and one or more of these loads could resolve the location.
gdb itself sometimes sets breakpoints in your program for
special purposes, such as proper handling of longjmp (in C
programs). These internal breakpoints are assigned negative numbers,
starting with -1; `info breakpoints' does not display them.
You can see these breakpoints with the gdb maintenance command
`maint info breakpoints' (see maint info breakpoints).
You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place where this may happen.
Depending on your system, watchpoints may be implemented in software or hardware. gdb does software watchpointing by single-stepping your program and testing the variable's value each time, which is hundreds of times slower than normal execution. (But this may still be worth it, to catch errors where you have no clue what part of your program is the culprit.)
On some systems, such as HP-UX, gnu/Linux and some other x86-based targets, gdb includes support for hardware watchpoints, which do not slow down the running of your program.
watch exprrwatch exprawatch exprinfo watchpointsinfo break.
gdb sets a hardware watchpoint if possible. Hardware watchpoints execute very quickly, and the debugger reports a change in value at the exact instruction where the change occurs. If gdb cannot set a hardware watchpoint, it sets a software watchpoint, which executes more slowly and reports the change in value at the next statement, not the instruction, after the change occurs.
When you issue the watch command, gdb reports
Hardware watchpoint num: expr
if it was able to set a hardware watchpoint.
Currently, the awatch and rwatch commands can only set
hardware watchpoints, because accesses to data that don't change the
value of the watched expression cannot be detected without examining
every instruction as it is being executed, and gdb does not do
that currently. If gdb finds that it is unable to set a
hardware breakpoint with the awatch or rwatch command, it
will print a message like this:
Expression cannot be implemented with read/access watchpoint.
Sometimes, gdb cannot set a hardware watchpoint because the data type of the watched expression is wider than what a hardware watchpoint on the target machine can handle. For example, some systems can only watch regions that are up to 4 bytes wide; on such systems you cannot set hardware watchpoints for an expression that yields a double-precision floating-point number (which is typically 8 bytes wide). As a work-around, it might be possible to break the large region into a series of smaller ones and watch them with separate watchpoints.
If you set too many hardware watchpoints, gdb might be unable to insert all of them when you resume the execution of your program. Since the precise number of active watchpoints is unknown until such time as the program is about to be resumed, gdb might not be able to warn you about this when you set the watchpoints, and the warning will be printed only when the program is resumed:
Hardware watchpoint num: Could not insert watchpoint
If this happens, delete or disable some of the watchpoints.
The SPARClite DSU will generate traps when a program accesses some data
or instruction address that is assigned to the debug registers. For the
data addresses, DSU facilitates the watch command. However the
hardware breakpoint registers can only take two data watchpoints, and
both watchpoints must be the same kind. For example, you can set two
watchpoints with watch commands, two with rwatch commands,
or two with awatch commands, but you cannot set one
watchpoint with one command and the other with a different command.
gdb will reject the command if you try to mix watchpoints.
Delete or disable unused watchpoint commands before setting new ones.
If you call a function interactively using print or call,
any watchpoints you have set will be inactive until gdb reaches another
kind of breakpoint or the call completes.
gdb automatically deletes watchpoints that watch local
(automatic) variables, or expressions that involve such variables, when
they go out of scope, that is, when the execution leaves the block in
which these variables were defined. In particular, when the program
being debugged terminates, all local variables go out of scope,
and so only watchpoints that watch global variables remain set. If you
rerun the program, you will need to set all such watchpoints again. One
way of doing that would be to set a code breakpoint at the entry to the
main function and when it breaks, set all the watchpoints.
Warning: In multi-thread programs, watchpoints have only limited usefulness. With the current watchpoint implementation, gdb can only watch the value of an expression in a single thread. If you are confident that the expression can only change due to the current thread's activity (and if you are also confident that no other thread can become current), then you can use watchpoints as usual. However, gdb may not notice when a non-current thread's activity changes the expression.HP-UX Warning: In multi-thread programs, software watchpoints have only limited usefulness. If gdb creates a software watchpoint, it can only watch the value of an expression in a single thread. If you are confident that the expression can only change due to the current thread's activity (and if you are also confident that no other thread can become current), then you can use software watchpoints as usual. However, gdb may not notice when a non-current thread's activity changes the expression. (Hardware watchpoints, in contrast, watch an expression in all threads.)
See set remote hardware-watchpoint-limit.
You can use catchpoints to cause the debugger to stop for certain
kinds of program events, such as C++ exceptions or the loading of a
shared library. Use the catch command to set a catchpoint.
catch eventthrowcatchexecexec. This is currently only available for HP-UX.
forkfork. This is currently only available for HP-UX.
vforkvfork. This is currently only available for HP-UX.
loadload libnameunloadunload libnametcatch eventUse the info break command to list the current catchpoints.
There are currently some limitations to C++ exception handling
(catch throw and catch catch) in gdb:
Sometimes catch is not the best way to debug exception handling:
if you need to know exactly where an exception is raised, it is better to
stop before the exception handler is called, since that way you
can see the stack before any unwinding takes place. If you set a
breakpoint in an exception handler instead, it may not be easy to find
out where the exception was raised.
To stop just before an exception handler is called, you need some
knowledge of the implementation. In the case of gnu C++, exceptions are
raised by calling a library function named __raise_exception
which has the following ANSI C interface:
/* addr is where the exception identifier is stored.
id is the exception identifier. */
void __raise_exception (void **addr, void *id);
To make the debugger catch all exceptions before any stack
unwinding takes place, set a breakpoint on __raise_exception
(see Breakpoints; watchpoints; and exceptions).
With a conditional breakpoint (see Break conditions) that depends on the value of id, you can stop your program when a specific exception is raised. You can use multiple conditional breakpoints to stop your program when any of a number of exceptions are raised.
It is often necessary to eliminate a breakpoint, watchpoint, or catchpoint once it has done its job and you no longer want your program to stop there. This is called deleting the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten.
With the clear command you can delete breakpoints according to
where they are in your program. With the delete command you can
delete individual breakpoints, watchpoints, or catchpoints by specifying
their breakpoint numbers.
It is not necessary to delete a breakpoint to proceed past it. gdb automatically ignores breakpoints on the first instruction to be executed when you continue execution without changing the execution address.
clearclear functionclear filename:functionclear linenumclear filename:linenumdelete [breakpoints] [range...]set
confirm off). You can abbreviate this command as d.
Rather than deleting a breakpoint, watchpoint, or catchpoint, you might prefer to disable it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can enable it again later.
You disable and enable breakpoints, watchpoints, and catchpoints with
the enable and disable commands, optionally specifying one
or more breakpoint numbers as arguments. Use info break or
info watch to print a list of breakpoints, watchpoints, and
catchpoints if you do not know which numbers to use.
A breakpoint, watchpoint, or catchpoint can have any of four different states of enablement:
break command starts out in this state.
tbreak command starts out in this state.
You can use the following commands to enable or disable breakpoints, watchpoints, and catchpoints:
disable [breakpoints] [range...]disable as dis.
enable [breakpoints] [range...]enable [breakpoints] once range...enable [breakpoints] delete range...Except for a breakpoint set with tbreak (see Setting breakpoints), breakpoints that you set are initially enabled;
subsequently, they become disabled or enabled only when you use one of
the commands above. (The command until can set and delete a
breakpoint of its own, but it does not change the state of your other
breakpoints; see Continuing and stepping.)
The simplest sort of breakpoint breaks every time your program reaches a specified place. You can also specify a condition for a breakpoint. A condition is just a Boolean expression in your programming language (see Expressions). A breakpoint with a condition evaluates the expression each time your program reaches it, and your program stops only if the condition is true.
This is the converse of using assertions for program validation; in that situation, you want to stop when the assertion is violated—that is, when the condition is false. In C, if you want to test an assertion expressed by the condition assert, you should set the condition `! assert' on the appropriate breakpoint.
Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow—but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one.
Break conditions can have side effects, and may even call functions in your program. This can be useful, for example, to activate functions that log program progress, or to use your own print functions to format special data structures. The effects are completely predictable unless there is another enabled breakpoint at the same address. (In that case, gdb might see the other breakpoint first and stop your program without checking the condition of this one.) Note that breakpoint commands are usually more convenient and flexible than break conditions for the purpose of performing side effects when a breakpoint is reached (see Breakpoint command lists).
Break conditions can be specified when a breakpoint is set, by using
`if' in the arguments to the break command. See Setting breakpoints. They can also be changed at any time
with the condition command.
You can also use the if keyword with the watch command.
The catch command does not recognize the if keyword;
condition is the only way to impose a further condition on a
catchpoint.
condition bnum expressioncondition, gdb checks expression immediately for
syntactic correctness, and to determine whether symbols in it have
referents in the context of your breakpoint. If expression uses
symbols not referenced in the context of the breakpoint, gdb
prints an error message:
No symbol "foo" in current context.
gdb does
not actually evaluate expression at the time the condition
command (or a command that sets a breakpoint with a condition, like
break if ...) is given, however. See Expressions.
condition bnumA special case of a breakpoint condition is to stop only when the breakpoint has been reached a certain number of times. This is so useful that there is a special way to do it, using the ignore count of the breakpoint. Every breakpoint has an ignore count, which is an integer. Most of the time, the ignore count is zero, and therefore has no effect. But if your program reaches a breakpoint whose ignore count is positive, then instead of stopping, it just decrements the ignore count by one and continues. As a result, if the ignore count value is n, the breakpoint does not stop the next n times your program reaches it.
ignore bnum countTo make the breakpoint stop the next time it is reached, specify a count of zero.
When you use continue to resume execution of your program from a
breakpoint, you can specify an ignore count directly as an argument to
continue, rather than using ignore. See Continuing and stepping.
If a breakpoint has a positive ignore count and a condition, the condition is not checked. Once the ignore count reaches zero, gdb resumes checking the condition.
You could achieve the effect of the ignore count with a condition such as `$foo-- <= 0' using a debugger convenience variable that is decremented each time. See Convenience variables.
Ignore counts apply to breakpoints, watchpoints, and catchpoints.
You can give any breakpoint (or watchpoint or catchpoint) a series of commands to execute when your program stops due to that breakpoint. For example, you might want to print the values of certain expressions, or enable other breakpoints.
commands [bnum]... command-list ...endend to terminate the commands.
To remove all commands from a breakpoint, type commands and
follow it immediately with end; that is, give no commands.
With no bnum argument, commands refers to the last
breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
recently encountered).
Pressing <RET> as a means of repeating the last gdb command is disabled within a command-list.
You can use breakpoint commands to start your program up again. Simply
use the continue command, or step, or any other command
that resumes execution.
Any other commands in the command list, after a command that resumes
execution, are ignored. This is because any time you resume execution
(even with a simple next or step), you may encounter
another breakpoint—which could have its own command list, leading to
ambiguities about which list to execute.
If the first command you specify in a command list is silent, the
usual message about stopping at a breakpoint is not printed. This may
be desirable for breakpoints that are to print a specific message and
then continue. If none of the remaining commands print anything, you
see no sign that the breakpoint was reached. silent is
meaningful only at the beginning of a breakpoint command list.
The commands echo, output, and printf allow you to
print precisely controlled output, and are often useful in silent
breakpoints. See Commands for controlled output.
For example, here is how you could use breakpoint commands to print the
value of x at entry to foo whenever x is positive.
break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end
One application for breakpoint commands is to compensate for one bug so
you can test for another. Put a breakpoint just after the erroneous line
of code, give it a condition to detect the case in which something
erroneous has been done, and give it commands to assign correct values
to any variables that need them. End with the continue command
so that your program does not stop, and start with the silent
command so that no output is produced. Here is an example:
break 403
commands
silent
set x = y + 4
cont
end
Some programming languages (notably C++ and Objective-C) permit a
single function name
to be defined several times, for application in different contexts.
This is called overloading. When a function name is overloaded,
`break function' is not enough to tell gdb where you want
a breakpoint. If you realize this is a problem, you can use
something like `break function(types)' to specify which
particular version of the function you want. Otherwise, gdb offers
you a menu of numbered choices for different possible breakpoints, and
waits for your selection with the prompt `>'. The first two
options are always `[0] cancel' and `[1] all'. Typing 1
sets a breakpoint at each definition of function, and typing
0 aborts the break command without setting any new
breakpoints.
For example, the following session excerpt shows an attempt to set a
breakpoint at the overloaded symbol String::after.
We choose three particular definitions of that function name:
(gdb) b String::after
[0] cancel
[1] all
[2] file:String.cc; line number:867
[3] file:String.cc; line number:860
[4] file:String.cc; line number:875
[5] file:String.cc; line number:853
[6] file:String.cc; line number:846
[7] file:String.cc; line number:735
> 2 4 6
Breakpoint 1 at 0xb26c: file String.cc, line 867.
Breakpoint 2 at 0xb344: file String.cc, line 875.
Breakpoint 3 at 0xafcc: file String.cc, line 846.
Multiple breakpoints were set.
Use the "delete" command to delete unwanted
breakpoints.
(gdb)
Under some operating systems, breakpoints cannot be used in a program if any other process is running that program. In this situation, attempting to run or continue a program with a breakpoint causes gdb to print an error message:
Cannot insert breakpoints.
The same program may be running in another process.
When this happens, you have three ways to proceed:
exec-file command to specify
that gdb should run your program under that name.
Then start your program again.
A similar message can be printed if you request too many active hardware-assisted breakpoints and watchpoints:
Stopped; cannot insert breakpoints.
You may have requested too many hardware breakpoints and watchpoints.
This message is printed when you attempt to resume the program, since only then gdb knows exactly how many hardware breakpoints and watchpoints it needs to insert.
When this message is printed, you need to disable or remove some of the hardware-assisted breakpoints and watchpoints, and then continue.
Some processor architectures place constraints on the addresses at which breakpoints may be placed. For architectures thus constrained, gdb will attempt to adjust the breakpoint's address to comply with the constraints dictated by the architecture.
One example of such an architecture is the Fujitsu FR-V. The FR-V is a VLIW architecture in which a number of RISC-like instructions may be bundled together for parallel execution. The FR-V architecture constrains the location of a breakpoint instruction within such a bundle to the instruction with the lowest address. gdb honors this constraint by adjusting a breakpoint's address to the first in the bundle.
It is not uncommon for optimized code to have bundles which contain instructions from different source statements, thus it may happen that a breakpoint's address will be adjusted from one source statement to another. Since this adjustment may significantly alter gdb's breakpoint related behavior from what the user expects, a warning is printed when the breakpoint is first set and also when the breakpoint is hit.
A warning like the one below is printed when setting a breakpoint that's been subject to address adjustment:
warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
Such warnings are printed both for user settable and gdb's internal breakpoints. If you see one of these warnings, you should verify that a breakpoint set at the adjusted address will have the desired affect. If not, the breakpoint in question may be removed and other breakpoints may be set which will have the desired behavior. E.g., it may be sufficient to place the breakpoint at a later instruction. A conditional breakpoint may also be useful in some cases to prevent the breakpoint from triggering too often.
gdb will also issue a warning when stopping at one of these adjusted breakpoints:
warning: Breakpoint 1 address previously adjusted from 0x00010414
to 0x00010410.
When this warning is encountered, it may be too late to take remedial action except in cases where the breakpoint is hit earlier or more frequently than expected.
Continuing means resuming program execution until your program
completes normally. In contrast, stepping means executing just
one more “step” of your program, where “step” may mean either one
line of source code, or one machine instruction (depending on what
particular command you use). Either when continuing or when stepping,
your program may stop even sooner, due to a breakpoint or a signal. (If
it stops due to a signal, you may want to use handle, or use
`signal 0' to resume execution. See Signals.)
continue [ignore-count]c [ignore-count]fg [ignore-count]ignore (see Break conditions).
The argument ignore-count is meaningful only when your program
stopped due to a breakpoint. At other times, the argument to
continue is ignored.
The synonyms c and fg (for foreground, as the
debugged program is deemed to be the foreground program) are provided
purely for convenience, and have exactly the same behavior as
continue.
To resume execution at a different place, you can use return
(see Returning from a function) to go back to the
calling function; or jump (see Continuing at a different address) to go to an arbitrary location in your program.
A typical technique for using stepping is to set a breakpoint (see Breakpoints; watchpoints; and catchpoints) at the beginning of the function or the section of your program where a problem is believed to lie, run your program until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen.
steps.
Warning: If you use thestepcommand while control is within a function that was compiled without debugging information, execution proceeds until control reaches a function that does have debugging information. Likewise, it will not step into a function which is compiled without debugging information. To step through functions without debugging information, use thestepicommand, described below.
The step command only stops at the first instruction of a source
line. This prevents the multiple stops that could otherwise occur in
switch statements, for loops, etc. step continues
to stop if a function that has debugging information is called within
the line. In other words, step steps inside any functions
called within the line.
Also, the step command only enters a function if there is line
number information for the function. Otherwise it acts like the
next command. This avoids problems when using cc -gl
on MIPS machines. Previously, step entered subroutines if there
was any debugging information about the routine.
step countstep, but do so count times. If a
breakpoint is reached, or a signal not related to stepping occurs before
count steps, stepping stops right away.
next [count]step, but function calls that appear within
the line of code are executed without stopping. Execution stops when
control reaches a different line of code at the original stack level
that was executing when you gave the next command. This command
is abbreviated n.
An argument count is a repeat count, as for step.
The next command only stops at the first instruction of a
source line. This prevents multiple stops that could otherwise occur in
switch statements, for loops, etc.
set step-modeset step-mode onset step-mode on command causes the step command to
stop at the first instruction of a function which contains no debug line
information rather than stepping over it.
This is useful in cases where you may be interested in inspecting the
machine instructions of a function which has no symbolic info and do not
want gdb to automatically skip over this function.
set step-mode offstep command to step over any functions which contains no
debug information. This is the default.
finishContrast this with the return command (see Returning from a function).
untilunext
command, except that when until encounters a jump, it
automatically continues execution until the program counter is greater
than the address of the jump.
This means that when you reach the end of a loop after single stepping
though it, until makes your program continue execution until it
exits the loop. In contrast, a next command at the end of a loop
simply steps back to the beginning of the loop, which forces you to step
through the next iteration.
until always stops your program if it attempts to exit the current
stack frame.
until may produce somewhat counterintuitive results if the order
of machine code does not match the order of the source lines. For
example, in the following excerpt from a debugging session, the f
(frame) command shows that execution is stopped at line
206; yet when we use until, we get to line 195:
(gdb) f
#0 main (argc=4, argv=0xf7fffae8) at m4.c:206
206 expand_input();
(gdb) until
195 for ( ; argc > 0; NEXTARG) {
This happened because, for execution efficiency, the compiler had
generated code for the loop closure test at the end, rather than the
start, of the loop—even though the test in a C for-loop is
written before the body of the loop. The until command appeared
to step back to the beginning of the loop when it advanced to this
expression; however, it has not really gone to an earlier
statement—not in terms of the actual machine code.
until with no argument works by means of single
instruction stepping, and hence is slower than until with an
argument.
until locationu locationbreak (see Setting breakpoints). This form of the command uses breakpoints, and
hence is quicker than until without an argument. The specified
location is actually reached only if it is in the current frame. This
implies that until can be used to skip over recursive function
invocations. For instance in the code below, if the current location is
line 96, issuing until 99 will execute the program up to
line 99 in the same invocation of factorial, i.e. after the inner
invocations have returned.
94 int factorial (int value)
95 {
96 if (value > 1) {
97 value *= factorial (value - 1);
98 }
99 return (value);
100 }
advance locationbreak
command. Execution will also stop upon exit from the current stack
frame. This command is similar to until, but advance will
not skip over recursive function calls, and the target location doesn't
have to be in the same frame as the current one.
stepistepi argsiIt is often useful to do `display/i $pc' when stepping by machine instructions. This makes gdb automatically display the next instruction to be executed, each time your program stops. See Automatic display.
An argument is a repeat count, as in step.
nextinexti argniAn argument is a repeat count, as in next.
A signal is an asynchronous event that can happen in a program. The
operating system defines the possible kinds of signals, and gives each
kind a name and a number. For example, in Unix SIGINT is the
signal a program gets when you type an interrupt character (often C-c);
SIGSEGV is the signal a program gets from referencing a place in
memory far away from all the areas in use; SIGALRM occurs when
the alarm clock timer goes off (which happens only if your program has
requested an alarm).
Some signals, including SIGALRM, are a normal part of the
functioning of your program. Others, such as SIGSEGV, indicate
errors; these signals are fatal (they kill your program immediately) if the
program has not specified in advance some other way to handle the signal.
SIGINT does not indicate an error in your program, but it is normally
fatal so it can carry out the purpose of the interrupt: to kill the program.
gdb has the ability to detect any occurrence of a signal in your program. You can tell gdb in advance what to do for each kind of signal.
Normally, gdb is set up to let the non-erroneous signals like
SIGALRM be silently passed to your program
(so as not to interfere with their role in the program's functioning)
but to stop your program immediately whenever an error signal happens.
You can change these settings with the handle command.
info signalsinfo handleinfo handle is an alias for info signals.
handle signal keywords...The keywords allowed by the handle command can be abbreviated.
Their full names are:
nostopstopprint keyword as well.
printnoprintnostop keyword as well.
passnoignorepass and noignore are synonyms.
nopassignorenopass and ignore are synonyms.
When a signal stops your program, the signal is not visible to the
program until you
continue. Your program sees the signal then, if pass is in
effect for the signal in question at that time. In other words,
after gdb reports a signal, you can use the handle
command with pass or nopass to control whether your
program sees that signal when you continue.
The default is set to nostop, noprint, pass for
non-erroneous signals such as SIGALRM, SIGWINCH and
SIGCHLD, and to stop, print, pass for the
erroneous signals.
You can also use the signal command to prevent your program from
seeing a signal, or cause it to see a signal it normally would not see,
or to give it any signal at any time. For example, if your program stopped
due to some sort of memory reference error, you might store correct
values into the erroneous variables and continue, hoping to see more
execution; but your program would probably terminate immediately as
a result of the fatal signal once it saw the signal. To prevent this,
you can continue with `signal 0'. See Giving your program a signal.
When your program has multiple threads (see Debugging programs with multiple threads), you can choose whether to set breakpoints on all threads, or on a particular thread.
break linespec thread threadnobreak linespec thread threadno if ...Use the qualifier `thread threadno' with a breakpoint command to specify that you only want gdb to stop the program when a particular thread reaches this breakpoint. threadno is one of the numeric thread identifiers assigned by gdb, shown in the first column of the `info threads' display.
If you do not specify `thread threadno' when you set a breakpoint, the breakpoint applies to all threads of your program.
You can use the thread qualifier on conditional breakpoints as
well; in this case, place `thread threadno' before the
breakpoint condition, like this:
(gdb) break frik.c:13 thread 28 if bartab > lim
Whenever your program stops under gdb for any reason, all threads of execution stop, not just the current thread. This allows you to examine the overall state of the program, including switching between threads, without worrying that things may change underfoot.
There is an unfortunate side effect. If one thread stops for a breakpoint, or for some other reason, and another thread is blocked in a system call, then the system call may return prematurely. This is a consequence of the interaction between multiple threads and the signals that gdb uses to implement breakpoints and other events that stop execution.
To handle this problem, your program should check the return value of each system call and react appropriately. This is good programming style anyways.
For example, do not write code like this:
sleep (10);
The call to sleep will return early if a different thread stops
at a breakpoint or for some other reason.
Instead, write this:
int unslept = 10;
while (unslept > 0)
unslept = sleep (unslept);
A system call is allowed to return early, so the system is still conforming to its specification. But gdb does cause your multi-threaded program to behave differently than it would without gdb.
Also, gdb uses internal breakpoints in the thread library to monitor certain events such as thread creation and thread destruction. When such an event happens, a system call in another thread may return prematurely, even though your program does not appear to stop.
Conversely, whenever you restart the program, all threads start
executing. This is true even when single-stepping with commands
like step or next.
In particular, gdb cannot single-step all threads in lockstep. Since thread scheduling is up to your debugging target's operating system (not controlled by gdb), other threads may execute more than one statement while the current thread completes a single step. Moreover, in general other threads stop in the middle of a statement, rather than at a clean statement boundary, when the program stops.
You might even find your program stopped in another thread after continuing or even single-stepping. This happens whenever some other thread runs into a breakpoint, a signal, or an exception before the first thread completes whatever you requested.
On some OSes, you can lock the OS scheduler and thus allow only a single thread to run.
set scheduler-locking modeoff, then there is no
locking and any thread may run at any time. If on, then only the
current thread may run when the inferior is resumed. The step
mode optimizes for single-stepping. It stops other threads from
“seizing the prompt” by preempting the current thread while you are
stepping. Other threads will only rarely (or never) get a chance to run
when you step. They are more likely to run when you `next' over a
function call, and they are completely free to run when you use commands
like `continue', `until', or `finish'. However, unless another
thread hits a breakpoint during its timeslice, they will never steal the
gdb prompt away from the thread that you are debugging.
show scheduler-lockingWhen your program has stopped, the first thing you need to know is where it stopped and how it got there.
Each time your program performs a function call, information about the call is generated. That information includes the location of the call in your program, the arguments of the call, and the local variables of the function being called. The information is saved in a block of data called a stack frame. The stack frames are allocated in a region of memory called the call stack.
When your program stops, the gdb commands for examining the stack allow you to see all of this information.
One of the stack frames is selected by gdb and many gdb commands refer implicitly to the selected frame. In particular, whenever you ask gdb for the value of a variable in your program, the value is found in the selected frame. There are special gdb commands to select whichever frame you are interested in. See Selecting a frame.
When your program stops, gdb automatically selects the
currently executing frame and describes it briefly, similar to the
frame command (see Information about a frame).
The call stack is divided up into contiguous pieces called stack frames, or frames for short; each frame is the data associated with one call to one function. The frame contains the arguments given to the function, the function's local variables, and the address at which the function is executing.
When your program is started, the stack has only one frame, that of the
function main. This is called the initial frame or the
outermost frame. Each time a function is called, a new frame is
made. Each time a function returns, the frame for that function invocation
is eliminated. If a function is recursive, there can be many frames for
the same function. The frame for the function in which execution is
actually occurring is called the innermost frame. This is the most
recently created of all the stack frames that still exist.
Inside your program, stack frames are identified by their addresses. A stack frame consists of many bytes, each of which has its own address; each kind of computer has a convention for choosing one byte whose address serves as the address of the frame. Usually this address is kept in a register called the frame pointer register while execution is going on in that frame.
gdb assigns numbers to all existing stack frames, starting with zero for the innermost frame, one for the frame that called it, and so on upward. These numbers do not really exist in your program; they are assigned by gdb to give you a way of designating stack frames in gdb commands.
Some compilers provide a way to compile functions so that they operate without stack frames. (For example, the gcc option
`-fomit-frame-pointer'
generates functions without a frame.) This is occasionally done with heavily used library functions to save the frame setup time. gdb has limited facilities for dealing with these function invocations. If the innermost function invocation has no stack frame, gdb nevertheless regards it as though it had a separate frame, which is numbered zero as usual, allowing correct tracing of the function call chain. However, gdb has no provision for frameless functions elsewhere in the stack.
frame argsframe command allows you to move from one stack frame to another,
and to print the stack frame you select. args may be either the
address of the frame or the stack frame number. Without an argument,
frame prints the current stack frame.
select-frameselect-frame command allows you to move from one stack frame
to another without printing the frame. This is the silent version of
frame.
A backtrace is a summary of how your program got where it is. It shows one line per frame, for many frames, starting with the currently executing frame (frame zero), followed by its caller (frame one), and on up the stack.
backtracebtYou can stop the backtrace at any time by typing the system interrupt
character, normally C-c.
backtrace nbt nbacktrace -nbt -nThe names where and info stack (abbreviated info s)
are additional aliases for backtrace.
Each line in the backtrace shows the frame number and the function name.
The program counter value is also shown—unless you use set
print address off. The backtrace also shows the source file name and
line number, as well as the arguments to the function. The program
counter value is omitted if it is at the beginning of the code for that
line number.
Here is an example of a backtrace. It was made with the command `bt 3', so it shows the innermost three frames.
#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
at builtin.c:993
#1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
#2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
at macro.c:71
(More stack frames follow...)
The display for frame zero does not begin with a program counter
value, indicating that your program has stopped at the beginning of the
code for line 993 of builtin.c.
Most programs have a standard user entry point—a place where system
libraries and startup code transition into user code. For C this is
main. When gdb finds the entry function in a backtrace
it will terminate the backtrace, to avoid tracing into highly
system-specific (and generally uninteresting) code.
If you need to examine the startup code, or limit the number of levels in a backtrace, you can change this behavior:
set backtrace past-mainset backtrace past-main onset backtrace past-main offshow backtrace past-mainset backtrace limit nset backtrace limit 0show backtrace limitMost commands for examining the stack and other data in your program work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected.
frame nf nmain.
frame addrf addrOn the SPARC architecture, frame needs two addresses to
select an arbitrary frame: a frame pointer and a stack pointer.
On the MIPS and Alpha architecture, it needs two addresses: a stack pointer and a program counter.
On the 29k architecture, it needs three addresses: a register stack pointer, a program counter, and a memory stack pointer.
up ndown ndown as do.
All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line.
For example:
(gdb) up
#1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
at env.c:10
10 read_input_file (argv[i]);
After such a printout, the list command with no arguments
prints ten lines centered on the point of execution in the frame.
You can also edit the program at the point of execution with your favorite
editing program by typing edit.
See Printing source lines,
for details.
up-silently ndown-silently nup and down,
respectively; they differ in that they do their work silently, without
causing display of the new frame. They are intended primarily for use
in gdb command scripts, where the output might be unnecessary and
distracting.
There are several other commands to print information about the selected stack frame.
frameff. With an
argument, this command is used to select a stack frame.
See Selecting a frame.
info frameinfo fThe verbose description is useful when
something has gone wrong that has made the stack format fail to fit
the usual conventions.
info frame addrinfo f addrframe command.
See Selecting a frame.
info argsinfo localsinfo catchup,
down, or frame commands); then type info catch.
See Setting catchpoints.
gdb can print parts of your program's source, since the debugging information recorded in the program tells gdb what source files were used to build it. When your program stops, gdb spontaneously prints the line where it stopped. Likewise, when you select a stack frame (see Selecting a frame), gdb prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command.
If you use gdb through its gnu Emacs interface, you may prefer to use Emacs facilities to view source; see Using gdb under gnu Emacs.
To print lines from a source file, use the list command
(abbreviated l). By default, ten lines are printed.
There are several ways to specify what part of the file you want to print.
Here are the forms of the list command most commonly used:
list linenumlist functionlistlist command, this prints lines following the last lines
printed; however, if the last line printed was a solitary line printed
as part of displaying a stack frame (see Examining the Stack), this prints lines centered around that line.
list -By default, gdb prints ten source lines with any of these forms of
the list command. You can change this using set listsize:
set listsize countlist command display count source lines (unless
the list argument explicitly specifies some other number).
show listsizelist prints.
Repeating a list command with <RET> discards the argument,
so it is equivalent to typing just list. This is more useful
than listing the same lines again. An exception is made for an
argument of `-'; that argument is preserved in repetition so that
each repetition moves up in the source file.
In general, the list command expects you to supply zero, one or two
linespecs. Linespecs specify source lines; there are several ways
of writing them, but the effect is always to specify some source line.
Here is a complete description of the possible arguments for list:
list linespeclist first,lastlist ,lastlist first,list +list -listHere are the ways of specifying a single source line—all the kinds of linespec.
list command has two linespecs, this refers to
the same source file as the first linespec.
+offsetlist command that has
two, this specifies the line offset lines down from the
first linespec.
-offset:number:function*address
To edit the lines in a source file, use the edit command.
The editing program of your choice
is invoked with the current line set to
the active line in the program.
Alternatively, there are several ways to specify what part of the file you
want to print if you want to see other parts of the program.
Here are the forms of the edit command most commonly used:
editedit numberedit functionedit filename:numberedit filename:functionedit *addressYou can customize gdb to use any editor you want
2. By default, it is /bin/ex, but you can change this
by setting the environment variable EDITOR before using
gdb. For example, to configure gdb to use the
vi editor, you could use these commands with the sh shell:
EDITOR=/usr/bin/vi
export EDITOR
gdb ...
or in the csh shell,
setenv EDITOR /usr/bin/vi
gdb ...
There are two commands for searching through the current source file for a regular expression.
forward-search regexpsearch regexpfo.
reverse-search regexprev.
Executable programs sometimes do not record the directories of the source files from which they were compiled, just the names. Even when they do, the directories could be moved between the compilation and your debugging session. gdb has a list of directories to search for source files; this is called the source path. Each time gdb wants a source file, it tries all the directories in the list, in the order they are present in the list, until it finds a file with the desired name. Note that the executable search path is not used for this purpose. Neither is the current working directory, unless it happens to be in the source path.
If gdb cannot find a source file in the source path, and the object program records a directory, gdb tries that directory too. If the source path is empty, and there is no record of the compilation directory, gdb looks in the current directory as a last resort.
Whenever you reset or rearrange the source path, gdb clears out any information it has cached about where source files are found and where each line is in the file.
When you start gdb, its source path includes only `cdir'
and `cwd', in that order.
To add other directories, use the directory command.
directory dirname ...dir dirname ...You can use the string `$cdir' to refer to the compilation
directory (if one is recorded), and `$cwd' to refer to the current
working directory. `$cwd' is not the same as `.'—the former
tracks the current working directory as it changes during your gdb
session, while the latter is immediately expanded to the current
directory at the time you add an entry to the source path.
directoryshow directoriesIf your source path is cluttered with directories that are no longer of interest, gdb may sometimes cause confusion by finding the wrong versions of source. You can correct the situation as follows:
directory with no argument to reset the source path to empty.
directory with suitable arguments to reinstall the
directories you want in the source path. You can add all the
directories in one command.
You can use the command info line to map source lines to program
addresses (and vice versa), and the command disassemble to display
a range of addresses as machine instructions. When run under gnu Emacs
mode, the info line command causes the arrow to point to the
line specified. Also, info line prints addresses in symbolic form as
well as hex.
info line linespeclist command (see Printing source lines).
For example, we can use info line to discover the location of
the object code for the first line of function
m4_changequote:
(gdb) info line m4_changequote
Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
We can also inquire (using *addr as the form for
linespec) what source line covers a particular address:
(gdb) info line *0x63ff
Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
After info line, the default address for the x command
is changed to the starting address of the line, so that `x/i' is
sufficient to begin examining the machine code (see Examining memory). Also, this address is saved as the value of the
convenience variable $_ (see Convenience variables).
disassembleThe following example shows the disassembly of a range of addresses of HP PA-RISC 2.0 code:
(gdb) disas 0x32c4 0x32e4
Dump of assembler code from 0x32c4 to 0x32e4:
0x32c4 <main+204>: addil 0,dp
0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
0x32cc <main+212>: ldil 0x3000,r31
0x32d0 <main+216>: ble 0x3f8(sr4,r31)
0x32d4 <main+220>: ldo 0(r31),rp
0x32d8 <main+224>: addil -0x800,dp
0x32dc <main+228>: ldo 0x588(r1),r26
0x32e0 <main+232>: ldil 0x3000,r31
End of assembler dump.
Some architectures have more than one commonly-used set of instruction mnemonics or other syntax.
set disassembly-flavor instruction-setdisassemble or x/i commands.
Currently this command is only defined for the Intel x86 family. You
can set instruction-set to either intel or att.
The default is att, the AT&T flavor used by default by Unix
assemblers for x86-based targets.
The usual way to examine data in your program is with the print
command (abbreviated p), or its synonym inspect. It
evaluates and prints the value of an expression of the language your
program is written in (see Using gdb with Different Languages).
print exprprint /f exprprintprint /fA more low-level way of examining data is with the x command.
It examines data in memory at a specified address and prints it in a
specified format. See Examining memory.
If you are interested in information about types, or about how the
fields of a struct or a class are declared, use the ptype exp
command rather than print. See Examining the Symbol Table.
print and many other gdb commands accept an expression and
compute its value. Any kind of constant, variable or operator defined
by the programming language you are using is valid in an expression in
gdb. This includes conditional expressions, function calls,
casts, and string constants. It also includes preprocessor macros, if
you compiled your program to include this information; see
Compilation.
gdb supports array constants in expressions input by
the user. The syntax is {element, element...}. For example,
you can use the command print {1, 2, 3} to build up an array in
memory that is malloced in the target program.
Because C is so widespread, most of the expressions shown in examples in this manual are in C. See Using gdb with Different Languages, for information on how to use expressions in other languages.
In this section, we discuss operators that you can use in gdb expressions regardless of your programming language.
Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer in order to examine a structure at that address in memory.
gdb supports these operators, in addition to those common to programming languages:
@::{type} addrThe most common kind of expression to use is the name of a variable in your program.
Variables in expressions are understood in the selected stack frame (see Selecting a frame); they must be either:
or
This means that in the function
foo (a)
int a;
{
bar (a);
{
int b = test ();
bar (b);
}
}
you can examine and use the variable a whenever your program is
executing within the function foo, but you can only use or
examine the variable b while your program is executing inside
the block where b is declared.
There is an exception: you can refer to a variable or function whose scope is a single source file even if the current execution point is not in this file. But it is possible to have more than one such variable or function with the same name (in different source files). If that happens, referring to that name has unpredictable effects. If you wish, you can specify a static variable in a particular function or file, using the colon-colon notation:
file::variable
function::variable
Here file or function is the name of the context for the
static variable. In the case of file names, you can use quotes to
make sure gdb parses the file name as a single word—for example,
to print a global value of x defined in f2.c:
(gdb) p 'f2.c'::x
This use of `::' is very rarely in conflict with the very similar use of the same notation in C++. gdb also supports use of the C++ scope resolution operator in gdb expressions.
Warning: Occasionally, a local variable may appear to have the wrong value at certain points in a function—just after entry to a new scope, and just before exit.You may see this problem when you are stepping by machine instructions. This is because, on most machines, it takes more than one instruction to set up a stack frame (including local variable definitions); if you are stepping by machine instructions, variables may appear to have the wrong values until the stack frame is completely built. On exit, it usually also takes more than one machine instruction to destroy a stack frame; after you begin stepping through that group of instructions, local variable definitions may be gone.
This may also happen when the compiler does significant optimizations. To be sure of always seeing accurate values, turn off all optimization when compiling.
Another possible effect of compiler optimizations is to optimize unused variables out of existence, or assign variables to registers (as opposed to memory addresses). Depending on the support for such cases offered by the debug info format used by the compiler, gdb might not be able to display values for such local variables. If that happens, gdb will print a message like this:
No symbol "foo" in current context.
To solve such problems, either recompile without optimizations, or use a different debug info format, if the compiler supports several such formats. For example, gcc, the gnu C/C++ compiler usually supports the -gstabs+ option. -gstabs+ produces debug info in a format that is superior to formats such as COFF. You may be able to use DWARF 2 (-gdwarf-2), which is also an effective form for debug info. See Options for Debugging Your Program or gnu CC.
It is often useful to print out several successive objects of the same type in memory; a section of an array, or an array of dynamically determined size for which only a pointer exists in the program.
You can do this by referring to a contiguous span of memory as an artificial array, using the binary operator `@'. The left operand of `@' should be the first element of the desired array and be an individual object. The right operand should be the desired length of the array. The result is an array value whose elements are all of the type of the left argument. The first element is actually the left argument; the second element comes from bytes of memory immediately following those that hold the first element, and so on. Here is an example. If a program says
int *array = (int *) malloc (len * sizeof (int));
you can print the contents of array with
p *array@len
The left operand of `@' must reside in memory. Array values made with `@' in this way behave just like other arrays in terms of subscripting, and are coerced to pointers when used in expressions. Artificial arrays most often appear in expressions via the value history (see Value history), after printing one out.
Another way to create an artificial array is to use a cast. This re-interprets a value as if it were an array. The value need not be in memory:
(gdb) p/x (short[2])0x12345678
$1 = {0x1234, 0x5678}
As a convenience, if you leave the array length out (as in `(type[])value') gdb calculates the size to fill the value (as `sizeof(value)/sizeof(type)':
(gdb) p/x (short[])0x12345678
$2 = {0x1234, 0x5678}
Sometimes the artificial array mechanism is not quite enough; in
moderately complex data structures, the elements of interest may not
actually be adjacent—for example, if you are interested in the values
of pointers in an array. One useful work-around in this situation is
to use a convenience variable (see Convenience variables) as a counter in an expression that prints the first
interesting value, and then repeat that expression via <RET>. For
instance, suppose you have an array dtab of pointers to
structures, and you are interested in the values of a field fv
in each structure. Here is an example of what you might type:
set $i = 0
p dtab[$i++]->fv
<RET>
<RET>
...
By default, gdb prints a value according to its data type. Sometimes this is not what you want. For example, you might want to print a number in hex, or a pointer in decimal. Or you might want to view data in memory at a certain address as a character string or as an instruction. To do these things, specify an output format when you print a value.
The simplest use of output formats is to say how to print a value
already computed. This is done by starting the arguments of the
print command with a slash and a format letter. The format
letters supported are:
xduota (gdb) p/a 0x54320
$3 = 0x54320 <_initialize_vx+396>
The command info symbol 0x54320 yields similar results.
See info symbol.
cfFor example, to print the program counter in hex (see Registers), type
p/x $pc
Note that no space is required before the slash; this is because command names in gdb cannot contain a slash.
To reprint the last value in the value history with a different format,
you can use the print command with just a format and no
expression. For example, `p/x' reprints the last value in hex.
You can use the command x (for “examine”) to examine memory in
any of several formats, independently of your program's data types.
x/nfu addrx addrxx command to examine memory.
n, f, and u are all optional parameters that specify how much memory to display and how to format it; addr is an expression giving the address where you want to start displaying memory. If you use defaults for nfu, you need not type the slash `/'. Several commands set convenient defaults for addr.
print,
`s' (null-terminated string), or `i' (machine instruction).
The default is `x' (hexadecimal) initially.
The default changes each time you use either x or print.
bhwgEach time you specify a unit size with x, that size becomes the
default unit the next time you use x. (For the `s' and
`i' formats, the unit size is ignored and is normally not written.)
info breakpoints (to
the address of the last breakpoint listed), info line (to the
starting address of a line), and print (if you use it to display
a value from memory).
For example, `x/3uh 0x54320' is a request to display three halfwords
(h) of memory, formatted as unsigned decimal integers (`u'),
starting at address 0x54320. `x/4xw $sp' prints the four
words (`w') of memory above the stack pointer (here, `$sp';
see Registers) in hexadecimal (`x').
Since the letters indicating unit sizes are all distinct from the letters specifying output formats, you do not have to remember whether unit size or format comes first; either order works. The output specifications `4xw' and `4wx' mean exactly the same thing. (However, the count n must come first; `wx4' does not work.)
Even though the unit size u is ignored for the formats `s'
and `i', you might still want to use a count n; for example,
`3i' specifies that you want to see three machine instructions,
including any operands. The command disassemble gives an
alternative way of inspecting machine instructions; see Source and machine code.
All the defaults for the arguments to x are designed to make it
easy to continue scanning memory with minimal specifications each time
you use x. For example, after you have inspected three machine
instructions with `x/3i addr', you can inspect the next seven
with just `x/7'. If you use <RET> to repeat the x command,
the repeat count n is used again; the other arguments default as
for successive uses of x.
The addresses and contents printed by the x command are not saved
in the value history because there is often too much of them and they
would get in the way. Instead, gdb makes these values available for
subsequent use in expressions as values of the convenience variables
$_ and $__. After an x command, the last address
examined is available for use in expressions in the convenience variable
$_. The contents of that address, as examined, are available in
the convenience variable $__.
If the x command has a repeat count, the address and contents saved
are from the last memory unit printed; this is not the same as the last
address printed if several units were printed on the last line of output.
If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the automatic display list so that gdb prints its value each time your program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this:
2: foo = 38
3: bar[5] = (struct hack *) 0x3804
This display shows item numbers, expressions and their current values. As with
displays you request manually using x or print, you can
specify the output format you prefer; in fact, display decides
whether to use print or x depending on how elaborate your
format specification is—it uses x if you specify a unit size,
or one of the two formats (`i' and `s') that are only
supported by x; otherwise it uses print.
display exprdisplay does not repeat if you press <RET> again after using it.
display/fmt exprdisplay/fmt addrFor example, `display/i $pc' can be helpful, to see the machine instruction about to be executed each time execution stops (`$pc' is a common name for the program counter; see Registers).
undisplay dnums...delete display dnums...undisplay does not repeat if you press <RET> after using it.
(Otherwise you would just get the error `No display number ...'.)
disable display dnums...enable display dnums...displayinfo displayIf a display expression refers to local variables, then it does not make
sense outside the lexical context for which it was set up. Such an
expression is disabled when execution enters a context where one of its
variables is not defined. For example, if you give the command
display last_char while inside a function with an argument
last_char, gdb displays this argument while your program
continues to stop inside that function. When it stops elsewhere—where
there is no variable last_char—the display is disabled
automatically. The next time your program stops where last_char
is meaningful, you can enable the display expression once again.
gdb provides the following ways to control how arrays, structures, and symbols are printed.
These settings are useful for debugging programs in any language:
set print addressset print address onon. For example, this is what a stack frame display looks like with
set print address on:
(gdb) f
#0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
at input.c:530
530 if (lquote != def_lquote)
set print address offset print address off:
(gdb) set print addr off
(gdb) f
#0 set_quotes (lq="<<", rq=">>") at input.c:530
530 if (lquote != def_lquote)
You can use `set print address off' to eliminate all machine
dependent displays from the gdb interface. For example, with
print address off, you should get the same text for backtraces on
all machines—whether or not they involve pointer arguments.
show print addressWhen gdb prints a symbolic address, it normally prints the
closest earlier symbol plus an offset. If that symbol does not uniquely
identify the address (for example, it is a name whose scope is a single
source file), you may need to clarify. One way to do this is with
info line, for example `info line *0x4537'. Alternately,
you can set gdb to print the source file and line number when
it prints a symbolic address:
set print symbol-filename onset print symbol-filename offshow print symbol-filenameAnother situation where it is helpful to show symbol filenames and line numbers is when disassembling code; gdb shows you the line number and source file that corresponds to each instruction.
Also, you may wish to see the symbolic form only if the address being printed is reasonably close to the closest earlier symbol:
set print max-symbolic-offset max-offsetshow print max-symbolic-offsetIf you have a pointer and you are not sure where it points, try
`set print symbol-filename on'. Then you can determine the name
and source file location of the variable where it points, using
`p/a pointer'. This interprets the address in symbolic form.
For example, here gdb shows that a variable ptt points
at another variable t, defined in hi2.c:
(gdb) set print symbol-filename on
(gdb) p/a ptt
$4 = 0xe008 <t in hi2.c>
Warning: For pointers that point to a local variable, `p/a'
does not show the symbol name and filename of the referent, even with
the appropriate set print options turned on.
Other settings control how different kinds of objects are printed:
set print arrayset print array onset print array offshow print arrayset print elements number-of-elementsset print elements command.
This limit also applies to the display of strings.
When gdb starts, this limit is set to 200.
Setting number-of-elements to zero means that the printing is unlimited.
show print elementsset print null-stopset print pretty on $1 = {
next = 0x0,
flags = {
sweet = 1,
sour = 1
},
meat = 0x54 "Pork"
}
set print pretty off $1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \
meat = 0x54 "Pork"}
This is the default format.
show print prettyset print sevenbit-strings on\nnn. This setting is
best if you are working in English (ascii) and you use the
high-order bit of characters as a marker or “meta” bit.
set print sevenbit-strings offshow print sevenbit-stringsset print union onset print union offshow print unionFor example, given the declarations
typedef enum {Tree, Bug} Species;
typedef enum {Big_tree, Acorn, Seedling} Tree_forms;
typedef enum {Caterpillar, Cocoon, Butterfly}
Bug_forms;
struct thing {
Species it;
union {
Tree_forms tree;
Bug_forms bug;
} form;
};
struct thing foo = {Tree, {Acorn}};
with set print union on in effect `p foo' would print
$1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}
and with set print union off in effect it would print
$1 = {it = Tree, form = {...}}
These settings are of interest when debugging C++ programs:
set print demangleset print demangle onshow print demangleset print asm-demangleset print asm-demangle onshow print asm-demangleset demangle-style styleautognug++) encoding algorithm.
This is the default.
hpaCC) encoding algorithm.
lucidlcc) encoding algorithm.
armcfront-generated executables. gdb would
require further enhancement to permit that.
show demangle-styleset print objectset print object onset print object offshow print objectset print static-membersset print static-members onset print static-members offshow print static-membersset print vtblset print vtbl onvtbl commands do not work on programs compiled with the HP
ANSI C++ compiler (aCC).)
set print vtbl offshow print vtblValues printed by the print command are saved in the gdb
value history. This allows you to refer to them in other expressions.
Values are kept until the symbol table is re-read or discarded
(for example with the file or symbol-file commands).
When the symbol table changes, the value history is discarded,
since the values may contain pointers back to the types defined in the
symbol table.
The values printed are given history numbers by which you can
refer to them. These are successive integers starting with one.
print shows you the history number assigned to a value by
printing `$num = ' before the value; here num is the
history number.
To refer to any previous value, use `$' followed by the value's
history number. The way print labels its output is designed to
remind you of this. Just $ refers to the most recent value in
the history, and $$ refers to the value before that.
$$n refers to the nth value from the end; $$2
is the value just prior to $$, $$1 is equivalent to
$$, and $$0 is equivalent to $.
For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type
p *$
If you have a chain of structures where the component next points
to the next one, you can print the contents of the next one with this:
p *$.next
You can print successive links in the chain by repeating this command—which you can do by just typing <RET>.
Note that the history records values, not expressions. If the value of
x is 4 and you type these commands:
print x
set x=5
then the value recorded in the value history by the print command
remains 4 even though the value of x has changed.
show valuesshow
values does not change the history.
show values nshow values +show values + produces no display.
Pressing <RET> to repeat show values n has exactly the
same effect as `show values +'.
gdb provides convenience variables that you can use within gdb to hold on to a value and refer to it later. These variables exist entirely within gdb; they are not part of your program, and setting a convenience variable has no direct effect on further execution of your program. That is why you can use them freely.
Convenience variables are prefixed with `$'. Any name preceded by `$' can be used for a convenience variable, unless it is one of the predefined machine-specific register names (see Registers). (Value history references, in contrast, are numbers preceded by `$'. See Value history.)
You can save a value in a convenience variable with an assignment expression, just as you would set a variable in your program. For example:
set $foo = *object_ptr
would save in $foo the value contained in the object pointed to by
object_ptr.
Using a convenience variable for the first time creates it, but its
value is void until you assign a new value. You can alter the
value with another assignment at any time.
Convenience variables have no fixed types. You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value.
show convenienceshow conv.
One of the ways to use a convenience variable is as a counter to be incremented or a pointer to be advanced. For example, to print a field from successive elements of an array of structures:
set $i = 0
print bar[$i++]->contents
Repeat that command by typing <RET>.
Some convenience variables are created automatically by gdb and given values likely to be useful.
$_$_ is automatically set by the x command to
the last address examined (see Examining memory). Other
commands which provide a default address for x to examine also
set $_ to that address; these commands include info line
and info breakpoint. The type of $_ is void *
except when set by the x command, in which case it is a pointer
to the type of $__.
$__$__ is automatically set by the x command
to the value found in the last address examined. Its type is chosen
to match the format in which the data was printed.
$_exitcode$_exitcode is automatically set to the exit code when
the program being debugged terminates.
On HP-UX systems, if you refer to a function or variable name that begins with a dollar sign, gdb searches for a user or system name first, before it searches for a convenience variable.
You can refer to machine register contents, in expressions, as variables
with names starting with `$'. The names of registers are different
for each machine; use info registers to see the names used on
your machine.
info registersinfo all-registersinfo registers regname ...gdb has four “standard” register names that are available (in
expressions) on most machines—whenever they do not conflict with an
architecture's canonical mnemonics for registers. The register names
$pc and $sp are used for the program counter register and
the stack pointer. $fp is used for a register that contains a
pointer to the current stack frame, and $ps is used for a
register that contains the processor status. For example,
you could print the program counter in hex with
p/x $pc
or print the instruction to be executed next with
x/i $pc
or add four to the stack pointer4 with
set $sp += 4
Whenever possible, these four standard register names are available on
your machine even though the machine has different canonical mnemonics,
so long as there is no conflict. The info registers command
shows the canonical names. For example, on the SPARC, info
registers displays the processor status register as $psr but you
can also refer to it as $ps; and on x86-based machines $ps
is an alias for the eflags register.
gdb always considers the contents of an ordinary register as an integer when the register is examined in this way. Some machines have special registers which can hold nothing but floating point; these registers are considered to have floating point values. There is no way to refer to the contents of an ordinary register as floating point value (although you can print it as a floating point value with `print/f $regname').
Some registers have distinct “raw” and “virtual” data formats. This
means that the data format in which the register contents are saved by
the operating system is not the same one that your program normally
sees. For example, the registers of the 68881 floating point
coprocessor are always saved in “extended” (raw) format, but all C
programs expect to work with “double” (virtual) format. In such
cases, gdb normally works with the virtual format only (the format
that makes sense for your program), but the info registers command
prints the data in both formats.
Normally, register values are relative to the selected stack frame (see Selecting a frame). This means that you get the value that the register would contain if all stack frames farther in were exited and their saved registers restored. In order to see the true contents of hardware registers, you must select the innermost frame (with `frame 0').
However, gdb must deduce where registers are saved, from the machine code generated by your compiler. If some registers are not saved, or if gdb is unable to locate the saved registers, the selected stack frame makes no difference.
Depending on the configuration, gdb may be able to give you more information about the status of the floating point hardware.
info floatDepending on the configuration, gdb may be able to give you more information about the status of the vector unit.
info vectorSome operating systems supply an auxiliary vector to programs at startup. This is akin to the arguments and environment that you specify for a program, but contains a system-dependent variety of binary values that tell system libraries important details about the hardware, operating system, and process. Each value's purpose is identified by an integer tag; the meanings are well-known but system-specific. Depending on the configuration and operating system facilities, gdb may be able to show you this information.
info auxvMemory region attributes allow you to describe special handling required by regions of your target's memory. gdb uses attributes to determine whether to allow certain types of memory accesses; whether to use specific width accesses; and whether to cache target memory.
Defined memory regions can be individually enabled and disabled. When a memory region is disabled, gdb uses the default attributes when accessing memory in that region. Similarly, if no memory regions have been defined, gdb uses the default attributes when accessing all memory.
When a memory region is defined, it is given a number to identify it; to enable, disable, or remove a memory region, you specify that number.
mem lower upper attributes...delete mem nums...disable mem nums...enable mem nums...info memThe access mode attributes set whether gdb may make read or write accesses to a memory region.
While these attributes prevent gdb from performing invalid memory accesses, they do nothing to prevent the target system, I/O DMA, etc. from accessing memory.
roworwThe acccess size attributes tells gdb to use specific sized accesses in the memory region. Often memory mapped device registers require specific sized accesses. If no access size attribute is specified, gdb may use accesses of any size.
8163264The data cache attributes set whether gdb will cache target memory. While this generally improves performance by reducing debug protocol overhead, it can lead to incorrect results because gdb does not know about volatile variables or memory mapped device registers.
cachenocache
You can use the commands dump, append, and
restore to copy data between target memory and a file. The
dump and append commands write data to a file, and the
restore command reads data from a file back into the inferior's
memory. Files may be in binary, Motorola S-record, Intel hex, or
Tektronix Hex format; however, gdb can only append to binary
files.
dump [format] memory filename start_addr end_addrdump [format] value filename exprThe format parameter may be any one of:
binaryihexsrectekhexgdb uses the same definitions of these formats as the gnu binary utilities, like `objdump' and `objcopy'. If format is omitted, gdb dumps the data in raw binary form.
append [binary] memory filename start_addr end_addrappend [binary] value filename exprrestore filename [binary] bias start endrestore command can automatically recognize any known bfd
file format, except for raw binary. To restore a raw binary file you
must specify the optional keyword binary after the filename.
If bias is non-zero, its value will be added to the addresses contained in the file. Binary files always start at address zero, so they will be restored at address bias. Other bfd files have a built-in location; they will be restored at offset bias from that location.
If start and/or end are non-zero, then only data between file offset start and file offset end will be restored. These offsets are relative to the addresses in the file, before the bias argument is applied.
If the program you are debugging uses a different character set to represent characters and strings than the one gdb uses itself, gdb can automatically translate between the character sets for you. The character set gdb uses we call the host character set; the one the inferior program uses we call the target character set.
For example, if you are running gdb on a gnu/Linux system, which
uses the ISO Latin 1 character set, but you are using gdb's
remote protocol (see Remote Debugging) to debug a program
running on an IBM mainframe, which uses the ebcdic character set,
then the host character set is Latin-1, and the target character set is
ebcdic. If you give gdb the command set
target-charset EBCDIC-US, then gdb translates between
ebcdic and Latin 1 as you print character or string values, or use
character and string literals in expressions.
gdb has no way to automatically recognize which character set
the inferior program uses; you must tell it, using the set
target-charset command, described below.
Here are the commands for controlling gdb's character set support:
set target-charset charsetset target-charset followed by <TAB><TAB>, gdb will
list the target character sets it supports.
set host-charset charsetBy default, gdb uses a host character set appropriate to the
system it is running on; you can override that default using the
set host-charset command.
gdb can only use certain character sets as its host character
set. We list the character set names gdb recognizes below, and
indicate which can be host character sets, but if you type
set target-charset followed by <TAB><TAB>, gdb will
list the host character sets it supports.
set charset charsetset charset followed by <TAB><TAB>,
gdb will list the name of the character sets that can be used
for both host and target.
show charsetshow host-charsetshow target-charsetgdb currently includes support for the following character sets:
ASCIIISO-8859-1EBCDIC-USIBM1047Note that these are all single-byte character sets. More work inside GDB is needed to support multi-byte or variable-width character encodings, like the UTF-8 and UCS-2 encodings of Unicode.
Here is an example of gdb's character set support in action. Assume that the following source code has been placed in the file charset-test.c:
#include <stdio.h>
char ascii_hello[]
= {72, 101, 108, 108, 111, 44, 32, 119,
111, 114, 108, 100, 33, 10, 0};
char ibm1047_hello[]
= {200, 133, 147, 147, 150, 107, 64, 166,
150, 153, 147, 132, 90, 37, 0};
main ()
{
printf ("Hello, world!\n");
}
In this program, ascii_hello and ibm1047_hello are arrays
containing the string `Hello, world!' followed by a newline,
encoded in the ascii and ibm1047 character sets.
We compile the program, and invoke the debugger on it:
$ gcc -g charset-test.c -o charset-test
$ gdb -nw charset-test
GNU gdb 2001-12-19-cvs
Copyright 2001 Free Software Foundation, Inc.
...
(gdb)
We can use the show charset command to see what character sets
gdb is currently using to interpret and display characters and
strings:
(gdb) show charset
The current host and target character set is `ISO-8859-1'.
(gdb)
For the sake of printing this manual, let's use ascii as our initial character set:
(gdb) set charset ASCII
(gdb) show charset
The current host and target character set is `ASCII'.
(gdb)
Let's assume that ascii is indeed the correct character set for our
host system — in other words, let's assume that if gdb prints
characters using the ascii character set, our terminal will display
them properly. Since our current target character set is also
ascii, the contents of ascii_hello print legibly:
(gdb) print ascii_hello
$1 = 0x401698 "Hello, world!\n"
(gdb) print ascii_hello[0]
$2 = 72 'H'
(gdb)
gdb uses the target character set for character and string literals you use in expressions:
(gdb) print '+'
$3 = 43 '+'
(gdb)
The ascii character set uses the number 43 to encode the `+' character.
gdb relies on the user to tell it which character set the
target program uses. If we print ibm1047_hello while our target
character set is still ascii, we get jibberish:
(gdb) print ibm1047_hello
$4 = 0x4016a8 "\310\205\223\223\226k@\246\226\231\223\204Z%"
(gdb) print ibm1047_hello[0]
$5 = 200 '\310'
(gdb)
If we invoke the set target-charset followed by <TAB><TAB>,
gdb tells us the character sets it supports:
(gdb) set target-charset
ASCII EBCDIC-US IBM1047 ISO-8859-1
(gdb) set target-charset
We can select ibm1047 as our target character set, and examine the
program's strings again. Now the ascii string is wrong, but
gdb translates the contents of ibm1047_hello from the
target character set, ibm1047, to the host character set,
ascii, and they display correctly:
(gdb) set target-charset IBM1047
(gdb) show charset
The current host character set is `ASCII'.
The current target character set is `IBM1047'.
(gdb) print ascii_hello
$6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
(gdb) print ascii_hello[0]
$7 = 72 '\110'
(gdb) print ibm1047_hello
$8 = 0x4016a8 "Hello, world!\n"
(gdb) print ibm1047_hello[0]
$9 = 200 'H'
(gdb)
As above, gdb uses the target character set for character and string literals you use in expressions:
(gdb) print '+'
$10 = 78 '+'
(gdb)
The ibm1047 character set uses the number 78 to encode the `+' character.
Some languages, such as C and C++, provide a way to define and invoke “preprocessor macros” which expand into strings of tokens. gdb can evaluate expressions containing macro invocations, show the result of macro expansion, and show a macro's definition, including where it was defined.
You may need to compile your program specially to provide gdb with information about preprocessor macros. Most compilers do not include macros in their debugging information, even when you compile with the -g flag. See Compilation.
A program may define a macro at one point, remove that definition later, and then provide a different definition after that. Thus, at different points in the program, a macro may have different definitions, or have no definition at all. If there is a current stack frame, gdb uses the macros in scope at that frame's source code line. Otherwise, gdb uses the macros in scope at the current listing location; see List.
At the moment, gdb does not support the ##
token-splicing operator, the # stringification operator, or
variable-arity macros.
Whenever gdb evaluates an expression, it always expands any macro invocations present in the expression. gdb also provides the following commands for working with macros explicitly.
macro expand expressionmacro exp expressionmacro expand-once expressionmacro exp1 expressioninfo macro macromacro define macro replacement-listmacro define macro(arglist) replacement-listA definition introduced by this command is in scope in every expression evaluated in gdb, until it is removed with the macro undef command, described below. The definition overrides all definitions for macro present in the program being debugged, as well as any previous user-supplied definition.
macro undef macroHere is a transcript showing the above commands in action. First, we show our source files:
$ cat sample.c
#include <stdio.h>
#include "sample.h"
#define M 42
#define ADD(x) (M + x)
main ()
{
#define N 28
printf ("Hello, world!\n");
#undef N
printf ("We're so creative.\n");
#define N 1729
printf ("Goodbye, world!\n");
}
$ cat sample.h
#define Q <
$
Now, we compile the program using the gnu C compiler, gcc. We pass the -gdwarf-2 and -g3 flags to ensure the compiler includes information about preprocessor macros in the debugging information.
$ gcc -gdwarf-2 -g3 sample.c -o sample
$
Now, we start gdb on our sample program:
$ gdb -nw sample
GNU gdb 2002-05-06-cvs
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, ...
(gdb)
We can expand macros and examine their definitions, even when the program is not running. gdb uses the current listing position to decide which macro definitions are in scope:
(gdb) list main
3
4 #define M 42
5 #define ADD(x) (M + x)
6
7 main ()
8 {
9 #define N 28
10 printf ("Hello, world!\n");
11 #undef N
12 printf ("We're so creative.\n");
(gdb) info macro ADD
Defined at /home/jimb/gdb/macros/play/sample.c:5
#define ADD(x) (M + x)
(gdb) info macro Q
Defined at /home/jimb/gdb/macros/play/sample.h:1
included at /home/jimb/gdb/macros/play/sample.c:2
#define Q <
(gdb) macro expand ADD(1)
expands to: (42 + 1)
(gdb) macro expand-once ADD(1)
expands to: once (M + 1)
(gdb)
In the example above, note that macro expand-once expands only
the macro invocation explicit in the original text — the invocation of
ADD — but does not expand the invocation of the macro M,
which was introduced by ADD.
Once the program is running, GDB uses the macro definitions in force at the source line of the current stack frame:
(gdb) break main
Breakpoint 1 at 0x8048370: file sample.c, line 10.
(gdb) run
Starting program: /home/jimb/gdb/macros/play/sample
Breakpoint 1, main () at sample.c:10
10 printf ("Hello, world!\n");
(gdb)
At line 10, the definition of the macro N at line 9 is in force:
(gdb) info macro N
Defined at /home/jimb/gdb/macros/play/sample.c:9
#define N 28
(gdb) macro expand N Q M
expands to: 28 < 42
(gdb) print N Q M
$1 = 1
(gdb)
As we step over directives that remove N's definition, and then
give it a new definition, gdb finds the definition (or lack
thereof) in force at each point:
(gdb) next
Hello, world!
12 printf ("We're so creative.\n");
(gdb) info macro N
The symbol `N' has no definition as a C/C++ preprocessor macro
at /home/jimb/gdb/macros/play/sample.c:12
(gdb) next
We're so creative.
14 printf ("Goodbye, world!\n");
(gdb) info macro N
Defined at /home/jimb/gdb/macros/play/sample.c:13
#define N 1729
(gdb) macro expand N Q M
expands to: 1729 < 42
(gdb) print N Q M
$2 = 0
(gdb)
In some applications, it is not feasible for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to change its behavior drastically, or perhaps fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it.
Using gdb's trace and collect commands, you can
specify locations in the program, called tracepoints, and
arbitrary expressions to evaluate when those tracepoints are reached.
Later, using the tfind command, you can examine the values
those expressions had when the program hit the tracepoints. The
expressions may also denote objects in memory—structures or arrays,
for example—whose values gdb should record; while visiting
a particular tracepoint, you may inspect those objects as if they were
in memory at that moment. However, because gdb records these
values without interacting with you, it can do so quickly and
unobtrusively, hopefully not disturbing the program's behavior.
The tracepoint facility is currently available only for remote targets. See Targets. In addition, your remote target must know how to collect trace data. This functionality is implemented in the remote stub; however, none of the stubs distributed with gdb support tracepoints as of this writing.
This chapter describes the tracepoint commands and features.
Before running such a trace experiment, an arbitrary number of tracepoints can be set. Like a breakpoint (see Set Breaks), a tracepoint has a number assigned to it by gdb. Like with breakpoints, tracepoint numbers are successive integers starting from one. Many of the commands associated with tracepoints take the tracepoint number as their argument, to identify which tracepoint to work on.
For each tracepoint, you can specify, in advance, some arbitrary set of data that you want the target to collect in the trace buffer when it hits that tracepoint. The collected data can include registers, local variables, or global data. Later, you can use gdb commands to examine the values these data had at the time the tracepoint was hit.
This section describes commands to set tracepoints and associated conditions and actions.
tracetrace command is very similar to the break command.
Its argument can be a source line, a function name, or an address in
the target program. See Set Breaks. The trace command
defines a tracepoint, which is a point in the target program where the
debugger will briefly stop, collect some data, and then allow the
program to continue. Setting a tracepoint or changing its commands
doesn't take effect until the next tstart command; thus, you
cannot change the tracepoint attributes once a trace experiment is
running.
Here are some examples of using the trace command:
(gdb) trace foo.c:121 // a source file and line number
(gdb) trace +2 // 2 lines forward
(gdb) trace my_function // first source line of function
(gdb) trace *my_function // EXACT start address of function
(gdb) trace *0x2117c4 // an address
You can abbreviate trace as tr.
The convenience variable $tpnum records the tracepoint number
of the most recently set tracepoint.
delete tracepoint [num]Examples:
(gdb) delete trace 1 2 3 // remove three tracepoints
(gdb) delete trace // remove all tracepoints
You can abbreviate this command as del tr.
disable tracepoint [num]enable tracepoint command.
enable tracepoint [num]passcount [n [num]]passcount command sets the
passcount of the most recently defined tracepoint. If no passcount is
given, the trace experiment will run until stopped explicitly by the
user.
Examples:
(gdb) passcount 5 2 // Stop on the 5th execution of
// tracepoint 2
(gdb) passcount 12 // Stop on the 12th execution of the
// most recently defined tracepoint.
(gdb) trace foo
(gdb) pass 3
(gdb) trace bar
(gdb) pass 2
(gdb) trace baz
(gdb) pass 1 // Stop tracing when foo has been
// executed 3 times OR when bar has
// been executed 2 times
// OR when baz has been executed 1 time.
actions [num]actions without bothering about its number). You specify the
actions themselves on the following lines, one action at a time, and
terminate the actions list with a line containing just end. So
far, the only defined actions are collect and
while-stepping.
To remove all actions from a tracepoint, type `actions num' and follow it immediately with `end'.
(gdb) collect data // collect some data
(gdb) while-stepping 5 // single-step 5 times, collect data
(gdb) end // signals the end of actions.
In the following example, the action list begins with collect
commands indicating the things to be collected when the tracepoint is
hit. Then, in order to single-step and collect additional data
following the tracepoint, a while-stepping command is used,
followed by the list of things to be collected while stepping. The
while-stepping command is terminated by its own separate
end command. Lastly, the action list is terminated by an
end command.
(gdb) trace foo
(gdb) actions
Enter actions for tracepoint 1, one per line:
> collect bar,baz
> collect $regs
> while-stepping 12
> collect $fp, $sp
> end
end
collect expr1, expr2, ...$regs$args$localsYou can give several consecutive collect commands, each one
with a single argument, or one collect command with several
arguments separated by commas: the effect is the same.
The command info scope (see info scope) is
particularly useful for figuring out what data to collect.
while-stepping nwhile-stepping command is
followed by the list of what to collect while stepping (followed by
its own end command):
> while-stepping 12
> collect $regs, myglobal
> end
>
You may abbreviate while-stepping as ws or
stepping.
info tracepoints [num]passcount n command
while-stepping n command
actions command
(gdb) info trace
Num Enb Address PassC StepC What
1 y 0x002117c4 0 0 <gdb_asm>
2 y 0x0020dc64 0 0 in g_test at g_test.c:1375
3 y 0x0020b1f4 0 0 in get_data at ../foo.c:41
(gdb)
This command can be abbreviated info tp.
tstarttstopNote: a trace experiment and data collection may stop automatically if any tracepoint's passcount is reached (see Tracepoint Passcounts), or if the trace buffer becomes full.
tstatusHere is an example of the commands we described so far:
(gdb) trace gdb_c_test
(gdb) actions
Enter actions for tracepoint #1, one per line.
> collect $regs,$locals,$args
> while-stepping 11
> collect $regs
> end
> end
(gdb) tstart
[time passes ...]
(gdb) tstop
After the tracepoint experiment ends, you use gdb commands
for examining the trace data. The basic idea is that each tracepoint
collects a trace snapshot every time it is hit and another
snapshot every time it single-steps. All these snapshots are
consecutively numbered from zero and go into a buffer, and you can
examine them later. The way you examine them is to focus on a
specific trace snapshot. When the remote stub is focused on a trace
snapshot, it will respond to all gdb requests for memory and
registers by reading from the buffer which belongs to that snapshot,
rather than from real memory or registers of the program being
debugged. This means that all gdb commands
(print, info registers, backtrace, etc.) will
behave as if we were currently debugging the program state as it was
when the tracepoint occurred. Any requests for data that are not in
the buffer will fail.
tfind nThe basic command for selecting a trace snapshot from the buffer is
tfind n, which finds trace snapshot number n,
counting from zero. If no argument n is given, the next
snapshot is selected.
Here are the various forms of using the tfind command.
tfind starttfind 0 (since 0 is the number of the first snapshot).
tfind nonetfind endtfindtfind -tfind tracepoint numtfind pc addrtfind outside addr1, addr2tfind range addr1, addr2tfind line [file:]ntfind line repeatedly can appear to have the same effect as
stepping from line to line in a live debugging session.
The default arguments for the tfind commands are specifically
designed to make it easy to scan through the trace buffer. For
instance, tfind with no argument selects the next trace
snapshot, and tfind - with no argument selects the previous
trace snapshot. So, by giving one tfind command, and then
simply hitting <RET> repeatedly you can examine all the trace
snapshots in order. Or, by saying tfind - and then hitting
<RET> repeatedly you can examine the snapshots in reverse order.
The tfind line command with no argument selects the snapshot
for the next source line executed. The tfind pc command with
no argument selects the next snapshot with the same program counter
(PC) as the current frame. The tfind tracepoint command with
no argument selects the next trace snapshot collected by the same
tracepoint as the current one.
In addition to letting you scan through the trace buffer manually, these commands make it easy to construct gdb scripts that scan through the trace buffer and print out whatever collected data you are interested in. Thus, if we want to examine the PC, FP, and SP registers from each trace frame in the buffer, we can say this:
(gdb) tfind start
(gdb) while ($trace_frame != -1)
> printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
$trace_frame, $pc, $sp, $fp
> tfind
> end
Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
Or, if we want to examine the variable X at each source line in
the buffer:
(gdb) tfind start
(gdb) while ($trace_frame != -1)
> printf "Frame %d, X == %d\n", $trace_frame, X
> tfind line
> end
Frame 0, X = 1
Frame 7, X = 2
Frame 13, X = 255
tdumpThis command takes no arguments. It prints all the data collected at the current trace snapshot.
(gdb) trace 444
(gdb) actions
Enter actions for tracepoint #2, one per line:
> collect $regs, $locals, $args, gdb_long_test
> end
(gdb) tstart
(gdb) tfind line 444
#0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
at gdb_test.c:444
444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
(gdb) tdump
Data collected at tracepoint 2, trace frame 1:
d0 0xc4aa0085 -995491707
d1 0x18 24
d2 0x80 128
d3 0x33 51
d4 0x71aea3d 119204413
d5 0x22 34
d6 0xe0 224
d7 0x380035 3670069
a0 0x19e24a 1696330
a1 0x3000668 50333288
a2 0x100 256
a3 0x322000 3284992
a4 0x3000698 50333336
a5 0x1ad3cc 1758156
fp 0x30bf3c 0x30bf3c
sp 0x30bf34 0x30bf34
ps 0x0 0
pc 0x20b2c8 0x20b2c8
fpcontrol 0x0 0
fpstatus 0x0 0
fpiaddr 0x0 0
p = 0x20e5b4 "gdb-test"
p1 = (void *) 0x11
p2 = (void *) 0x22
p3 = (void *) 0x33
p4 = (void *) 0x44
p5 = (void *) 0x55
p6 = (void *) 0x66
gdb_long_test = 17 '\021'
(gdb)
save-tracepoints filename
This command saves all current tracepoint definitions together with
their actions and passcounts, into a file filename
suitable for use in a later debugging session. To read the saved
tracepoint definitions, use the source command (see Command Files).
(int) $trace_frame(int) $tracepoint(int) $trace_line(char []) $trace_file(char []) $trace_func$tracepoint.
Note: $trace_file is not suitable for use in printf,
use output instead.
Here's a simple example of using these convenience variables for stepping through all the trace snapshots and printing some of their data.
(gdb) tfind start
(gdb) while $trace_frame != -1
> output $trace_file
> printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
> tfind
> end
If your program is too large to fit completely in your target system's memory, you can sometimes use overlays to work around this problem. gdb provides some support for debugging programs that use overlays.
Suppose you have a computer whose instruction address space is only 64 kilobytes long, but which has much more memory which can be accessed by other means: special instructions, segment registers, or memory management hardware, for example. Suppose further that you want to adapt a program which is larger than 64 kilobytes to run on this system.
One solution is to identify modules of your program which are relatively independent, and need not call each other directly; call these modules overlays. Separate the overlays from the main program, and place their machine code in the larger memory. Place your main program in instruction memory, but leave at least enough space there to hold the largest overlay as well.
Now, to call a function located in an overlay, you must first copy that overlay's machine code from the large memory into the space set aside for it in the instruction memory, and then jump to its entry point there.
Data Instruction Larger
Address Space Address Space Address Space
+-----------+ +-----------+ +-----------+
| | | | | |
+-----------+ +-----------+ +-----------+<-- overlay 1
| program | | main | .----| overlay 1 | load address
| variables | | program | | +-----------+
| and heap | | | | | |
+-----------+ | | | +-----------+<-- overlay 2
| | +-----------+ | | | load address
+-----------+ | | | .-| overlay 2 |
| | | | | |
mapped --->+-----------+ | | +-----------+
address | | | | | |
| overlay | <-' | | |
| area | <---' +-----------+<-- overlay 3
| | <---. | | load address
+-----------+ `--| overlay 3 |
| | | |
+-----------+ | |
+-----------+
| |
+-----------+
A code overlay
The diagram (see A code overlay) shows a system with separate data and instruction address spaces. To map an overlay, the program copies its code from the larger address space to the instruction address space. Since the overlays shown here all use the same mapped address, only one may be mapped at a time. For a system with a single address space for data and instructions, the diagram would be similar, except that the program variables and heap would share an address space with the main program and the overlay area.
An overlay loaded into instruction memory and ready for use is called a mapped overlay; its mapped address is its address in the instruction memory. An overlay not present (or only partially present) in instruction memory is called unmapped; its load address is its address in the larger memory. The mapped address is also called the virtual memory address, or VMA; the load address is also called the load memory address, or LMA.
Unfortunately, overlays are not a completely transparent way to adapt a program to limited instruction memory. They introduce a new set of global constraints you must keep in mind as you design your program:
The overlay system described above is rather simple, and could be improved in many ways:
To use gdb's overlay support, each overlay in your program must correspond to a separate section of the executable file. The section's virtual memory address and load memory address must be the overlay's mapped and load addresses. Identifying overlays with sections allows gdb to determine the appropriate address of a function or variable, depending on whether the overlay is mapped or not.
gdb's overlay commands all start with the word overlay;
you can abbreviate this as ov or ovly. The commands are:
overlay offoverlay manualoverlay map-overlay and overlay unmap-overlay
commands described below.
overlay map-overlay overlayoverlay map overlayoverlay unmap-overlay overlayoverlay unmap overlayoverlay autooverlay load-targetoverlay loadoverlay list-overlaysoverlay listNormally, when gdb prints a code address, it includes the name of the function the address falls in:
(gdb) print main
$3 = {int ()} 0x11a0 <main>
When overlay debugging is enabled, gdb recognizes code in
unmapped overlays, and prints the names of unmapped functions with
asterisks around them. For example, if foo is a function in an
unmapped overlay, gdb prints it this way:
(gdb) overlay list
No sections are mapped.
(gdb) print foo
$5 = {int (int)} 0x100000 <*foo*>
When foo's overlay is mapped, gdb prints the function's
name normally:
(gdb) overlay list
Section .ov.foo.text, loaded at 0x100000 - 0x100034,
mapped at 0x1016 - 0x104a
(gdb) print foo
$6 = {int (int)} 0x1016 <foo>
When overlay debugging is enabled, gdb can find the correct
address for functions and variables in an overlay, whether or not the
overlay is mapped. This allows most gdb commands, like
break and disassemble, to work normally, even on unmapped
code. However, gdb's breakpoint support has some limitations:
gdb can automatically track which overlays are mapped and which
are not, given some simple co-operation from the overlay manager in the
inferior. If you enable automatic overlay debugging with the
overlay auto command (see Overlay Commands), gdb
looks in the inferior's memory for certain variables describing the
current state of the overlays.
Here are the variables your overlay manager must define to support gdb's automatic overlay debugging:
_ovly_table: struct
{
/* The overlay's mapped address. */
unsigned long vma;
/* The size of the overlay, in bytes. */
unsigned long size;
/* The overlay's load address. */
unsigned long lma;
/* Non-zero if the overlay is currently mapped;
zero otherwise. */
unsigned long mapped;
}
_novlys:_ovly_table.
To decide whether a particular overlay is mapped or not, gdb
looks for an entry in _ovly_table whose vma and
lma members equal the VMA and LMA of the overlay's section in the
executable file. When gdb finds a matching entry, it consults
the entry's mapped member to determine whether the overlay is
currently mapped.
In addition, your overlay manager may define a function called
_ovly_debug_event. If this function is defined, gdb
will silently set a breakpoint there. If the overlay manager then
calls this function whenever it has changed the overlay table, this
will enable gdb to accurately keep track of which overlays
are in program memory, and update any breakpoints that may be set
in overlays. This will allow breakpoints to work even if the
overlays are kept in ROM or other non-writable memory while they
are not being executed.
When linking a program which uses overlays, you must place the overlays at their load addresses, while relocating them to run at their mapped addresses. To do this, you must write a linker script (see Overlay Description). Unfortunately, since linker scripts are specific to a particular host system, target architecture, and target memory layout, this manual cannot provide portable sample code demonstrating gdb's overlay support.
However, the gdb source distribution does contain an overlaid program, with linker scripts for a few systems, as part of its test suite. The program consists of the following files from gdb/testsuite/gdb.base:
d10v-elf
and m32r-elf targets.
You can build the test program using the d10v-elf GCC
cross-compiler like this:
$ d10v-elf-gcc -g -c overlays.c
$ d10v-elf-gcc -g -c ovlymgr.c
$ d10v-elf-gcc -g -c foo.c
$ d10v-elf-gcc -g -c bar.c
$ d10v-elf-gcc -g -c baz.c
$ d10v-elf-gcc -g -c grbx.c
$ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
baz.o grbx.o -Wl,-Td10v.ld -o overlays
The build process is identical for any other architecture, except that
you must substitute the appropriate compiler and linker script for the
target system for d10v-elf-gcc and d10v.ld.
Although programming languages generally have common aspects, they are
rarely expressed in the same manner. For instance, in ANSI C,
dereferencing a pointer p is accomplished by *p, but in
Modula-2, it is accomplished by p^. Values can also be
represented (and displayed) differently. Hex numbers in C appear as
`0x1ae', while in Modula-2 they appear as `1AEH'.
Language-specific information is built into gdb for some languages, allowing you to express operations like the above in your program's native language, and allowing gdb to output values in a manner consistent with the syntax of your program's native language. The language you use to build expressions is called the working language.
There are two ways to control the working language—either have gdb
set it automatically, or select it manually yourself. You can use the
set language command for either purpose. On startup, gdb
defaults to setting the language automatically. The working language is
used to determine how expressions you type are interpreted, how values
are printed, etc.
In addition to the working language, every source file that
gdb knows about has its own working language. For some object
file formats, the compiler might indicate which language a particular
source file is in. However, most of the time gdb infers the
language from the name of the file. The language of a source file
controls whether C++ names are demangled—this way backtrace can
show each frame appropriately for its own language. There is no way to
set the language of a source file from within gdb, but you can
set the language associated with a filename extension. See Displaying the language.
This is most commonly a problem when you use a program, such
as cfront or f2c, that generates C but is written in
another language. In that case, make the
program use #line directives in its C output; that way
gdb will know the correct language of the source code of the original
program, and will display that source code, not the generated C code.
If a source file name ends in one of the following extensions, then gdb infers that its language is the one indicated.
In addition, you may set the language associated with a filename extension. See Displaying the language.
If you allow gdb to set the language automatically, expressions are interpreted the same way in your debugging session and your program.
If you wish, you may set the language manually. To do this, issue the
command `set language lang', where lang is the name of
a language, such as
c or modula-2.
For a list of the supported languages, type `set language'.
Setting the language manually prevents gdb from updating the working language automatically. This can lead to confusion if you try to debug a program when the working language is not the same as the source language, when an expression is acceptable to both languages—but means different things. For instance, if the current source file were written in C, and gdb was parsing Modula-2, a command such as:
print a = b + c
might not have the effect you intended. In C, this means to add
b and c and place the result in a. The result
printed would be the value of a. In Modula-2, this means to compare
a to the result of b+c, yielding a BOOLEAN value.
To have gdb set the working language automatically, use `set language local' or `set language auto'. gdb then infers the working language. That is, when your program stops in a frame (usually by encountering a breakpoint), gdb sets the working language to the language recorded for the function in that frame. If the language for a frame is unknown (that is, if the function or block corresponding to the frame was defined in a source file that does not have a recognized extension), the current working language is not changed, and gdb issues a warning.
This may not seem necessary for most programs, which are written entirely in one source language. However, program modules and libraries written in one source language can be used by a main program written in a different source language. Using `set language auto' in this case frees you from having to set the working language manually.
The following commands help you find out which language is the working language, and also what language source files were written in.
show languageprint to
build and compute expressions that may involve variables in your program.
info frameinfo sourceIn unusual circumstances, you may have source files with extensions not in the standard list. You can then set the extension associated with a language explicitly:
set extension-language .ext languageinfo extensionsWarning: In this release, the gdb commands for type and range checking are included, but they do not yet have any effect. This section documents the intended facilities.
Some languages are designed to guard you against making seemingly common errors through a series of compile- and run-time checks. These include checking the type of arguments to functions and operators, and making sure mathematical overflows are caught at run time. Checks such as these help to ensure a program's correctness once it has been compiled by eliminating type mismatches, and providing active checks for range errors when your program is running.
gdb can check for conditions like the above if you wish.
Although gdb does not check the statements in your program, it
can check expressions entered directly into gdb for evaluation via
the print command, for example. As with the working language,
gdb can also decide whether or not to check automatically based on
your program's source language. See Supported languages,
for the default settings of supported languages.
Some languages, such as Modula-2, are strongly typed, meaning that the arguments to operators and functions have to be of the correct type, otherwise an error occurs. These checks prevent type mismatch errors from ever causing any run-time problems. For example,
1 + 2 => 3
but
error--> 1 + 2.3
The second example fails because the CARDINAL 1 is not
type-compatible with the REAL 2.3.
For the expressions you use in gdb commands, you can tell the gdb type checker to skip checking; to treat any mismatches as errors and abandon the expression; or to only issue warnings when type mismatches occur, but evaluate the expression anyway. When you choose the last of these, gdb evaluates expressions like the second example above, but also issues a warning.
Even if you turn type checking off, there may be other reasons
related to type that prevent gdb from evaluating an expression.
For instance, gdb does not know how to add an int and
a struct foo. These particular type errors have nothing to do
with the language in use, and usually arise from expressions, such as
the one described above, which make little sense to evaluate anyway.
Each language defines to what degree it is strict about type. For instance, both Modula-2 and C require the arguments to arithmetical operators to be numbers. In C, enumerated types and pointers can be represented as numbers, so that they are valid arguments to mathematical operators. See Supported languages, for further details on specific languages.
gdb provides some additional commands for controlling the type checker:
set check type autoset check type onset check type offset check type warnshow typeIn some languages (such as Modula-2), it is an error to exceed the bounds of a type; this is enforced with run-time checks. Such range checking is meant to ensure program correctness by making sure computations do not overflow, or indices on an array element access do not exceed the bounds of the array.
For expressions you use in gdb commands, you can tell gdb to treat range errors in one of three ways: ignore them, always treat them as errors and abandon the expression, or issue warnings but evaluate the expression anyway.
A range error can result from numerical overflow, from exceeding an array index bound, or when you type a constant that is not a member of any type. Some languages, however, do not treat overflows as an error. In many implementations of C, mathematical overflow causes the result to “wrap around” to lower values—for example, if m is the largest integer value, and s is the smallest, then
m + 1 => s
This, too, is specific to individual languages, and in some cases specific to individual compilers or machines. See Supported languages, for further details on specific languages.
gdb provides some additional commands for controlling the range checker:
set check range autoset check range onset check range offset check range warnshow rangegdb supports C, C++, Objective-C, Fortran, Java, assembly, and Modula-2.
Some gdb features may be used in expressions regardless of the
language you use: the gdb @ and :: operators,
and the `{type}addr' construct (see Expressions) can be used with the constructs of any supported
language.
The following sections detail to what degree each source language is supported by gdb. These sections are not meant to be language tutorials or references, but serve only as a reference guide to what the gdb expression parser accepts, and what input and output formats should look like for different languages. There are many good books written on each of these languages; please look to these for a language reference or tutorial.
Since C and C++ are so closely related, many features of gdb apply to both languages. Whenever this is the case, we discuss those languages together.
The C++ debugging facilities are jointly implemented by the C++
compiler and gdb. Therefore, to debug your C++ code
effectively, you must compile your C++ programs with a supported
C++ compiler, such as gnu g++, or the HP ANSI C++
compiler (aCC).
For best results when using gnu C++, use the DWARF 2 debugging
format; if it doesn't work on your system, try the stabs+ debugging
format. You can select those formats explicitly with the g++
command-line options -gdwarf-2 and -gstabs+.
See Options for Debugging Your Program or gnu CC.
Operators must be defined on values of specific types. For instance,
+ is defined on numbers, but not on structures. Operators are
often defined on groups of types.
For the purposes of C and C++, the following definitions hold:
int with any of its storage-class
specifiers; char; enum; and, for C++, bool.
float, double, and
long double (if supported by the target platform).
(type *).
The following operators are supported. They are listed here in order of increasing precedence:
,== op= b,
and translated to a = a op b.
op= and = have the same precedence.
op is any one of the operators |, ^, &,
<<, >>, +, -, *, /, %.
?: ? b : c can be thought
of as: if a then b else c. a should be of an
integral type.
||&&|^&==, !=<, >, <=, >=<<, >>@+, -*, /, %++, --*++.
&++.
For debugging C++, gdb implements a use of `&' beyond what is
allowed in the C++ language itself: you can use `&(&ref)'
(or, if you prefer, simply `&&ref') to examine the address
where a C++ reference variable (declared with `&ref') is
stored.
-++.
!++.
~++.
., ->struct and union data.
.*, ->*[][i] is defined as
*(a+i). Same precedence as ->.
()->.
::struct, union,
and class types.
::::,
above.
If an operator is redefined in the user code, gdb usually attempts to invoke the redefined version instead of using the operator's predefined meaning.
gdb allows you to express the constants of C and C++ in the following ways:
long value.
float (as opposed to the default double) type; or with
a letter `l' or `L', which specifies a long double
constant.
'), or a number—the ordinal value of the corresponding character
(usually its ascii value). Within quotes, the single character may
be represented by a letter or by escape sequences, which are of
the form `\nnn', where nnn is the octal representation
of the character's ordinal value; or of the form `\x', where
`x' is a predefined special character—for example,
`\n' for newline.
"). Any valid character constant (as described
above) may appear. Double quotes within the string must be preceded by
a backslash, so for instance `"a\"b'c"' is a string of five
characters.
gdb expression handling can interpret most C++ expressions.
Warning: gdb can only debug C++ code if you use the proper compiler and the proper debug format. Currently, gdb works best when debugging C++ code that is compiled with gcc 2.95.3 or with gcc 3.1 or newer, using the options -gdwarf-2 or -gstabs+. DWARF 2 is preferred over stabs+. Most configurations of gcc emit either DWARF 2 or stabs+ as their default debug format, so you usually don't need to specify a debug format explicitly. Other compilers and/or debug formats are likely to work badly or not at all when using gdb to debug C++ code.
count = aml->GetOriginal(x, y)
this following the same rules as C++.
It does perform integral conversions and promotions, floating-point promotions, arithmetic conversions, pointer conversions, conversions of class objects to base classes, and standard conversions such as those of functions or arrays to pointers; it requires an exact match on the number of function arguments.
Overload resolution is always performed, unless you have specified
set overload-resolution off. See gdb features for C++.
You must specify set overload-resolution off in order to use an
explicit function signature to call an overloaded function, as in
p 'foo(char,int)'('x', 13)
The gdb command-completion facility can simplify this; see Command completion.
In the parameter list shown when gdb displays a frame, the values of reference variables are not displayed (unlike other variables); this avoids clutter, since references are often used for large structures. The address of a reference variable is always shown, unless you have specified `set print address off'.
::—your
expressions can use it just as expressions in your program do. Since
one scope may be defined in another, you can use :: repeatedly if
necessary, for example in an expression like
`scope1::scope2::name'. gdb also allows
resolving name scope by reference to source files, in both C and C++
debugging (see Program variables).
In addition, when used with HP's C++ compiler, gdb supports calling virtual functions correctly, printing out virtual bases of objects, calling functions in a base subobject, casting objects, and invoking user-defined operators.
If you allow gdb to set type and range checking automatically, they
both default to off whenever the working language changes to
C or C++. This happens regardless of whether you or gdb
selects the working language.
If you allow gdb to set the language automatically, it recognizes source files whose names end with .c, .C, or .cc, etc, and when gdb enters code compiled from one of these files, it sets the working language to C or C++. See Having gdb infer the source language, for further details.
By default, when gdb parses C or C++ expressions, type checking is not used. However, if you turn type checking on, gdb considers two variables type equivalent if:
typedef.
Range checking, if turned on, is done on mathematical operations. Array indices are not checked, since they are often used to index a pointer that is not itself an array.
The set print union and show print union commands apply to
the union type. When set to `on', any union that is
inside a struct or class is also printed. Otherwise, it
appears as `{...}'.
The @ operator aids in the debugging of dynamic arrays, formed
with pointers and a memory allocation function. See Expressions.
Some gdb commands are particularly useful with C++, and some are designed specifically for use with C++. Here is a summary:
rbreak regexcatch throwcatch catchptype typenameset print demangleshow print demangleset print asm-demangleshow print asm-demangleset print objectshow print objectset print vtblshow print vtblvtbl commands do not work on programs compiled with the HP
ANSI C++ compiler (aCC).)
set overload-resolution onset overload-resolution off(types) rather than just symbol. You can
also use the gdb command-line word completion facilities to list the
available choices, or to finish the type list for you.
See Command completion, for details on how to do this.
This section provides information about some commands and command options that are useful for debugging Objective-C code.
The following commands have been extended to accept Objective-C method names as line specifications:
clear
break
info line
jump
list
A fully qualified Objective-C method name is specified as
-[Class methodName]
where the minus sign is used to indicate an instance method and a
plus sign (not shown) is used to indicate a class method. The class
name Class and method name methodName are enclosed in
brackets, similar to the way messages are specified in Objective-C
source code. For example, to set a breakpoint at the create
instance method of class Fruit in the program currently being
debugged, enter:
break -[Fruit create]
To list ten program lines around the initialize class method,
enter:
list +[NSText initialize]
In the current version of gdb, the plus or minus sign is required. In future versions of gdb, the plus or minus sign will be optional, but you can use it to narrow the search. It is also possible to specify just a method name:
break create
You must specify the complete method name, including any colons. If
your program's source files contain more than one create method,
you'll be presented with a numbered list of classes that implement that
method. Indicate your choice by number, or type `0' to exit if
none apply.
As another example, to clear a breakpoint established at the
makeKeyAndOrderFront: method of the NSWindow class, enter:
clear -[NSWindow makeKeyAndOrderFront:]
The print command has also been extended to accept methods. For example:
print -[object hash]
will tell gdb to send the hash message to object
and print the result. Also, an additional command has been added,
print-object or po for short, which is meant to print
the description of an object. However, this command may only work
with certain Objective-C libraries that have a particular hook
function, _NSPrintForDebugger, defined.
The extensions made to gdb to support Modula-2 only support output from the gnu Modula-2 compiler (which is currently being developed). Other Modula-2 compilers are not currently supported, and attempting to debug executables produced by them is most likely to give an error as gdb reads in the executable's symbol table.
Operators must be defined on values of specific types. For instance,
+ is defined on numbers, but not on structures. Operators are
often defined on groups of types. For the purposes of Modula-2, the
following definitions hold:
INTEGER, CARDINAL, and
their subranges.
CHAR and its subranges.
REAL.
POINTER TO
type.
SET and BITSET types.
BOOLEAN.
The following operators are supported, and appear in order of increasing precedence:
,:=:= value is
value.
<, ><=, >=<.
=, <>, #<. In gdb scripts, only <> is
available for inequality, since # conflicts with the script
comment character.
IN<.
ORAND, &@+, -*/*.
DIV, MOD*.
-INTEGER and REAL data.
^NOT^.
.RECORD field selector. Defined on RECORD data. Same
precedence as ^.
[]ARRAY data. Same precedence as ^.
()PROCEDURE objects. Same precedence
as ^.
::, .Warning: Sets and their operations are not yet supported, so gdb treats the use of the operatorIN, or the use of operators+,-,*,/,=, ,<>,#,<=, and>=on sets as an error.
Modula-2 also makes available several built-in procedures and functions. In describing these, the following metavariables are used:
ARRAY variable.
CHAR constant or variable.
SET OF mtype (where mtype is the type of m).
All Modula-2 built-in procedures also return a result, described below.
ABS(n)CAP(c)CHR(i)DEC(v)DEC(v,i)EXCL(m,s)FLOAT(i)HIGH(a)INC(v)INC(v,i)INCL(m,s)MAX(t)MIN(t)ODD(i)ORD(x)SIZE(x)TRUNC(r)VAL(t,i)Warning: Sets and their operations are not yet supported, so gdb treats the use of proceduresINCLandEXCLas an error.
gdb allows you to express the constants of Modula-2 in the following ways:
') or double ("). They may
also be expressed by their ordinal value (their ascii value, usually)
followed by a `C'.
') or double (").
Escape sequences in the style of C are also allowed. See C and C++ constants, for a brief explanation of escape
sequences.
TRUE and
FALSE.
If type and range checking are set automatically by gdb, they
both default to on whenever the working language changes to
Modula-2. This happens regardless of whether you or gdb
selected the working language.
If you allow gdb to set the language automatically, then entering code compiled from a file whose name ends with .mod sets the working language to Modula-2. See Having gdb set the language automatically, for further details.
A few changes have been made to make Modula-2 programs easier to debug. This is done primarily via loosening its type strictness:
:=) returns the value of its right-hand
argument.
Warning: in this release, gdb does not yet perform type or range checking.
gdb considers two Modula-2 variables type equivalent if:
TYPE
t1 = t2 statement
As long as type checking is enabled, any attempt to combine variables whose types are not equivalent is an error.
Range checking is done on all mathematical operations, assignment, array index bounds, and all built-in functions and procedures.
:: and .
There are a few subtle differences between the Modula-2 scope operator
(.) and the gdb scope operator (::). The two have
similar syntax:
module . id
scope :: id
where scope is the name of a module or a procedure, module the name of a module, and id is any declared identifier within your program, except another module.
Using the :: operator makes gdb search the scope
specified by scope for the identifier id. If it is not
found in the specified scope, then gdb searches all scopes
enclosing the one specified by scope.
Using the . operator makes gdb search the current scope for
the identifier specified by id that was imported from the
definition module specified by module. With this operator, it is
an error if the identifier id was not imported from definition
module module, or if id is not an identifier in
module.
Some gdb commands have little use when debugging Modula-2 programs.
Five subcommands of set print and show print apply
specifically to C and C++: `vtbl', `demangle',
`asm-demangle', `object', and `union'. The first four
apply to C++, and the last to the C union type, which has no direct
analogue in Modula-2.
The @ operator (see Expressions), while available
with any language, is not useful with Modula-2. Its
intent is to aid the debugging of dynamic arrays, which cannot be
created in Modula-2 as they can in C or C++. However, because an
address can be specified by an integral constant, the construct
`{type}adrexp' is still useful.
In gdb scripts, the Modula-2 inequality operator # is
interpreted as the beginning of a comment. Use <> instead.
In addition to the other fully-supported programming languages,
gdb also provides a pseudo-language, called minimal.
It does not represent a real programming language, but provides a set
of capabilities close to what the C or assembly languages provide.
This should allow most simple operations to be performed while debugging
an application that uses a language currently not supported by gdb.
If the language is set to auto, gdb will automatically
select this language if the current frame corresponds to an unsupported
language.
The commands described in this chapter allow you to inquire about the symbols (names of variables, functions and types) defined in your program. This information is inherent in the text of your program and does not change as your program executes. gdb finds it in your program's symbol table, in the file indicated when you started gdb (see Choosing files), or by one of the file-management commands (see Commands to specify files).
Occasionally, you may need to refer to symbols that contain unusual characters, which gdb ordinarily treats as word delimiters. The most frequent case is in referring to static variables in other source files (see Program variables). File names are recorded in object files as debugging symbols, but gdb would ordinarily parse a typical file name, like foo.c, as the three words `foo' `.' `c'. To allow gdb to recognize `foo.c' as a single symbol, enclose it in single quotes; for example,
p 'foo.c'::x
looks up the value of x in the scope of the file foo.c.
info address symbolNote the contrast with `print &symbol', which does not work at all for a register variable, and for a stack local variable prints the exact address of the current instantiation of the variable.
info symbol addr (gdb) info symbol 0x54320
_initialize_vx + 396 in section .text
This is the opposite of the info address command. You can use
it to find out the name of a variable or a function given its address.
whatis exprwhatis$, the last value in the value history.
ptype typenameptype exprptypeptype
differs from whatis by printing a detailed description, instead
of just the name of the type.
For example, for this variable declaration:
struct complex {double real; double imag;} v;
the two commands give this output:
(gdb) whatis v
type = struct complex
(gdb) ptype v
type = struct complex {
double real;
double imag;
}
As with whatis, using ptype without an argument refers to
the type of $, the last value in the value history.
info types regexpinfo typesvalue, but `i type ^value$' gives
information only on types whose complete name is value.
This command differs from ptype in two ways: first, like
whatis, it does not print a detailed description; second, it
lists all source files where a type is defined.
info scope addr (gdb) info scope command_line_handler
Scope for command_line_handler:
Symbol rl is an argument at stack/frame offset 8, length 4.
Symbol linebuffer is in static storage at address 0x150a18, length 4.
Symbol linelength is in static storage at address 0x150a1c, length 4.
Symbol p is a local variable in register $esi, length 4.
Symbol p1 is a local variable in register $ebx, length 4.
Symbol nline is a local variable in register $edx, length 4.
Symbol repeat is a local variable at frame offset -8, length 4.
This command is especially useful for determining what data to collect during a trace experiment, see collect.
info sourceinfo sourcesinfo functionsinfo functions regexpstep; `info fun ^step' finds those whose names
start with step. If a function name contains characters
that conflict with the regular expression language (eg.
`operator*()'), they may be quoted with a backslash.
info variablesinfo variables regexpinfo classesinfo classes regexpinfo selectorsinfo selectors regexpSome systems allow individual object files that make up your program to be replaced without stopping and restarting your program. For example, in VxWorks you can simply recompile a defective object file and keep on running. If you are running on one of these systems, you can allow gdb to reload the symbols for automatically relinked modules:
set symbol-reloading onset symbol-reloading offsymbol-reloading off, since otherwise gdb
may discard symbols when linking large programs, that may contain
several modules (from different directories or libraries) with the same
name.
show symbol-reloadingon or off setting.
set opaque-type-resolution onstruct, class, or
union—for example, struct MyType *—that is used in one
source file although the full declaration of struct MyType is in
another source file. The default is on.
A change in the setting of this subcommand will not take effect until
the next time symbols for a file are loaded.
set opaque-type-resolution off {<no data fields>}
show opaque-type-resolutionmaint print symbols filenamemaint print psymbols filenamemaint print msymbols filenameinfo sources to find out which files these are. If you
use `maint print psymbols' instead, the dump shows information about
symbols that gdb only knows partially—that is, symbols defined in
files that gdb has skimmed, but not yet read completely. Finally,
`maint print msymbols' dumps just the minimal symbol information
required for each object file from which gdb has read some symbols.
See Commands to specify files, for a discussion of how
gdb reads symbols (in the description of symbol-file).
maint info symtabs [ regexp ]maint info psymtabs [ regexp ]struct symtab or struct partial_symtab
structures whose names match regexp. If regexp is not
given, list them all. The output includes expressions which you can
copy into a gdb debugging this one to examine a particular
structure in more detail. For example:
(gdb) maint info psymtabs dwarf2read
{ objfile /home/gnu/build/gdb/gdb
((struct objfile *) 0x82e69d0)
{ psymtab /home/gnu/src/gdb/dwarf2read.c
((struct partial_symtab *) 0x8474b10)
readin no
fullname (null)
text addresses 0x814d3c8 -- 0x8158074
globals (* (struct partial_symbol **) 0x8507a08 @ 9)
statics (* (struct partial_symbol **) 0x40e95b78 @ 2882)
dependencies (none)
}
}
(gdb) maint info symtabs
(gdb)
We see that there is one partial symbol table whose filename contains the string `dwarf2read', belonging to the `gdb' executable; and we see that gdb has not read in any symtabs yet at all. If we set a breakpoint on a function, that will cause gdb to read the symtab for the compilation unit containing that function:
(gdb) break dwarf2_psymtab_to_symtab
Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
line 1574.
(gdb) maint info symtabs
{ objfile /home/gnu/build/gdb/gdb
((struct objfile *) 0x82e69d0)
{ symtab /home/gnu/src/gdb/dwarf2read.c
((struct symtab *) 0x86c1f38)
dirname (null)
fullname (null)
blockvector ((struct blockvector *) 0x86c1bd0) (primary)
debugformat DWARF 2
}
}
(gdb)
Once you think you have found an error in your program, you might want to find out for certain whether correcting the apparent error would lead to correct results in the rest of the run. You can find the answer by experiment, using the gdb features for altering execution of the program.
For example, you can store new values into variables or memory locations, give your program a signal, restart it at a different address, or even return prematurely from a function.
To alter the value of a variable, evaluate an assignment expression. See Expressions. For example,
print x=4
stores the value 4 into the variable x, and then prints the
value of the assignment expression (which is 4).
See Using gdb with Different Languages, for more
information on operators in supported languages.
If you are not interested in seeing the value of the assignment, use the
set command instead of the print command. set is
really the same as print except that the expression's value is
not printed and is not put in the value history (see Value history). The expression is evaluated only for its effects.
If the beginning of the argument string of the set command
appears identical to a set subcommand, use the set
variable command instead of just set. This command is identical
to set except for its lack of subcommands. For example, if your
program has a variable width, you get an error if you try to set
a new value with just `set width=13', because gdb has the
command set width:
(gdb) whatis width
type = double
(gdb) p width
$4 = 13
(gdb) set width=47
Invalid syntax in expression.
The invalid expression, of course, is `=47'. In
order to actually set the program's variable width, use
(gdb) set var width=47
Because the set command has many subcommands that can conflict
with the names of program variables, it is a good idea to use the
set variable command instead of just set. For example, if
your program has a variable g, you run into problems if you try
to set a new value with just `set g=4', because gdb has
the command set gnutarget, abbreviated set g:
(gdb) whatis g
type = double
(gdb) p g
$1 = 1
(gdb) set g=4
(gdb) p g
$2 = 1
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/smith/cc_progs/a.out
"/home/smith/cc_progs/a.out": can't open to read symbols:
Invalid bfd target.
(gdb) show g
The current BFD target is "=4".
The program variable g did not change, and you silently set the
gnutarget to an invalid value. In order to set the variable
g, use
(gdb) set var g=4
gdb allows more implicit conversions in assignments than C; you can freely store an integer value into a pointer variable or vice versa, and you can convert any structure to any other structure that is the same length or shorter.
To store values into arbitrary places in memory, use the `{...}'
construct to generate a value of specified type at a specified address
(see Expressions). For example, {int}0x83040 refers
to memory location 0x83040 as an integer (which implies a certain size
and representation in memory), and
set {int}0x83040 = 4
stores the value 4 into that memory location.
Ordinarily, when you continue your program, you do so at the place where
it stopped, with the continue command. You can instead continue at
an address of your own choosing, with the following commands:
jump linespectbreak command
in conjunction with jump. See Setting breakpoints.
The jump command does not change the current stack frame, or
the stack pointer, or the contents of any memory location or any
register other than the program counter. If line linespec is in
a different function from the one currently executing, the results may
be bizarre if the two functions expect different patterns of arguments or
of local variables. For this reason, the jump command requests
confirmation if the specified line is not in the function currently
executing. However, even bizarre results are predictable if you are
well acquainted with the machine-language code of your program.
jump *addressOn many systems, you can get much the same effect as the jump
command by storing a new value into the register $pc. The
difference is that this does not start your program running; it only
changes the address of where it will run when you continue. For
example,
set $pc = 0x485
makes the next continue command or stepping command execute at
address 0x485, rather than at the address where your program stopped.
See Continuing and stepping.
The most common occasion to use the jump command is to back
up—perhaps with more breakpoints set—over a portion of a program
that has already executed, in order to examine its execution in more
detail.
signal signalsignal 2 and signal
SIGINT are both ways of sending an interrupt signal.
Alternatively, if signal is zero, continue execution without
giving a signal. This is useful when your program stopped on account of
a signal and would ordinary see the signal when resumed with the
continue command; `signal 0' causes it to resume without a
signal.
signal does not repeat when you press <RET> a second time
after executing the command.
Invoking the signal command is not the same as invoking the
kill utility from the shell. Sending a signal with kill
causes gdb to decide what to do with the signal depending on
the signal handling tables (see Signals). The signal command
passes the signal directly to your program.
returnreturn expressionreturn
command. If you give an
expression argument, its value is used as the function's return
value.
When you use return, gdb discards the selected stack frame
(and all frames within it). You can think of this as making the
discarded frame return prematurely. If you wish to specify a value to
be returned, give that value as the argument to return.
This pops the selected stack frame (see Selecting a frame), and any other frames inside of it, leaving its caller as the innermost remaining frame. That frame becomes selected. The specified value is stored in the registers used for returning values of functions.
The return command does not resume execution; it leaves the
program stopped in the state that would exist if the function had just
returned. In contrast, the finish command (see Continuing and stepping) resumes execution until the
selected stack frame returns naturally.
call exprvoid
returned values.
You can use this variant of the print command if you want to
execute a function from your program, but without cluttering the output
with void returned values. If the result is not void, it
is printed and saved in the value history.
By default, gdb opens the file containing your program's executable code (or the corefile) read-only. This prevents accidental alterations to machine code; but it also prevents you from intentionally patching your program's binary.
If you'd like to be able to patch the binary, you can specify that
explicitly with the set write command. For example, you might
want to turn on internal debugging flags, or even to make emergency
repairs.
set write onset write offIf you have already loaded a file, you must load it again (using the
exec-file or core-file command) after changing set
write, for your new setting to take effect.
show writegdb needs to know the file name of the program to be debugged, both in order to read its symbol table and in order to start your program. To debug a core dump of a previous run, you must also tell gdb the name of the core dump file.
You may want to specify executable and core dump file names. The usual way to do this is at start-up time, using the arguments to gdb's start-up commands (see Getting In and Out of gdb).
Occasionally it is necessary to change to a different file during a gdb session. Or you may run gdb and forget to specify a file you want to use. In these situations the gdb commands to specify new files are useful.
file filenamerun command. If you do not specify a
directory and the file is not found in the gdb working directory,
gdb uses the environment variable PATH as a list of
directories to search, just as the shell does when looking for a program
to run. You can change the value of this variable, for both gdb
and your program, using the path command.
On systems with memory-mapped files, an auxiliary file named
filename.syms may hold symbol table information for
filename. If so, gdb maps in the symbol table from
filename.syms, starting up more quickly. See the
descriptions of the file options `-mapped' and `-readnow'
(available on the command line, and with the commands file,
symbol-file, or add-symbol-file, described below),
for more information.
filefile with no argument makes gdb discard any information it
has on both executable file and the symbol table.
exec-file [ filename ]PATH
if necessary to locate your program. Omitting filename means to
discard information on the executable file.
symbol-file [ filename ]PATH is
searched when necessary. Use the file command to get both symbol
table and program to run from the same file.
symbol-file with no argument clears out gdb information on your
program's symbol table.
The symbol-file command causes gdb to forget the contents
of its convenience variables, the value history, and all breakpoints and
auto-display expressions. This is because they may contain pointers to
the internal data recording symbols and data types, which are part of
the old symbol table data being discarded inside gdb.
symbol-file does not repeat if you press <RET> again after
executing it once.
When gdb is configured for a particular environment, it
understands debugging information in whatever format is the standard
generated for that environment; you may use either a gnu compiler, or
other compilers that adhere to the local conventions.
Best results are usually obtained from gnu compilers; for example,
using gcc you can generate debugging information for
optimized code.
For most kinds of object files, with the exception of old SVR3 systems
using COFF, the symbol-file command does not normally read the
symbol table in full right away. Instead, it scans the symbol table
quickly to find which source files and which symbols are present. The
details are read later, one source file at a time, as they are needed.
The purpose of this two-stage reading strategy is to make gdb
start up faster. For the most part, it is invisible except for
occasional pauses while the symbol table details for a particular source
file are being read. (The set verbose command can turn these
pauses into messages if desired. See Optional warnings and messages.)
We have not implemented the two-stage strategy for COFF yet. When the
symbol table is stored in COFF format, symbol-file reads the
symbol table data in full right away. Note that “stabs-in-COFF”
still does the two-stage strategy, since the debug info is actually
in stabs format.
symbol-file filename [ -readnow ] [ -mapped ]file filename [ -readnow ] [ -mapped ]If memory-mapped files are available on your system through the
mmap system call, you can use another option, `-mapped', to
cause gdb to write the symbols for your program into a reusable
file. Future gdb debugging sessions map in symbol information
from this auxiliary symbol file (if the program has not changed), rather
than spending time reading the symbol table from the executable
program. Using the `-mapped' option has the same effect as
starting gdb with the `-mapped' command-line option.
You can use both options together, to make sure the auxiliary symbol file has all the symbol information for your program.
The auxiliary symbol file for a program called myprog is called `myprog.syms'. Once this file exists (so long as it is newer than the corresponding executable), gdb always attempts to use it when you debug myprog; no special options or commands are needed.
The .syms file is specific to the host machine where you run gdb. It holds an exact image of the internal gdb symbol table. It cannot be shared across multiple host platforms.
core-file [ filename ]core-file with no argument specifies that no core file is
to be used.
Note that the core file is ignored when your program is actually running
under gdb. So, if you have been running your program and you
wish to debug a core file instead, you must kill the subprocess in which
the program is running. To do this, use the kill command
(see Killing the child process).
add-symbol-file filename addressadd-symbol-file filename address [ -readnow ] [ -mapped ]add-symbol-file filename -ssection address ...add-symbol-file command reads additional symbol table
information from the file filename. You would use this command
when filename has been dynamically loaded (by some other means)
into the program that is running. address should be the memory
address at which the file has been loaded; gdb cannot figure
this out for itself. You can additionally specify an arbitrary number
of `-ssection address' pairs, to give an explicit
section name and base address for that section. You can specify any
address as an expression.
The symbol table of the file filename is added to the symbol table
originally read with the symbol-file command. You can use the
add-symbol-file command any number of times; the new symbol data
thus read keeps adding to the old. To discard all old symbol data
instead, use the symbol-file command without any arguments.
Although filename is typically a shared library file, an executable file, or some other object file which has been fully relocated for loading into a process, you can also load symbolic information from relocatable .o files, as long as:
add-symbol-file command.
Some embedded operating systems, like Sun Chorus and VxWorks, can load
relocatable files into an already running program; such systems
typically make the requirements above easy to meet. However, it's
important to recognize that many native systems use complex link
procedures (.linkonce section factoring and C++ constructor table
assembly, for example) that make the requirements difficult to meet. In
general, one cannot assume that using add-symbol-file to read a
relocatable object file's symbolic information will have the same effect
as linking the relocatable object file into the program in the normal
way.
add-symbol-file does not repeat if you press <RET> after using it.
You can use the `-mapped' and `-readnow' options just as with
the symbol-file command, to change how gdb manages the symbol
table information for filename.
add-shared-symbol-fileadd-shared-symbol-file command can be used only under Harris' CXUX
operating system for the Motorola 88k. gdb automatically looks for
shared libraries, however if gdb does not find yours, you can run
add-shared-symbol-file. It takes no arguments.
sectionsection command changes the base address of section SECTION of
the exec file to ADDR. This can be used if the exec file does not contain
section addresses, (such as in the a.out format), or when the addresses
specified in the file itself are wrong. Each section must be changed
separately. The info files command, described below, lists all
the sections and their addresses.
info filesinfo targetinfo files and info target are synonymous; both print the
current target (see Specifying a Debugging Target),
including the names of the executable and core dump files currently in
use by gdb, and the files from which symbols were loaded. The
command help target lists all possible targets rather than
current ones.
maint info sectionsmaint info sections. In addition to the section information
displayed by info files, this command displays the flags and file
offset of each section in the executable and core dump files. In addition,
maint info sections provides the following command options (which
may be arbitrarily combined):
ALLOBJALLOCLOAD.bss sections.
RELOCREADONLYCODEDATAROMCONSTRUCTORHAS_CONTENTSNEVER_LOADCOFF_SHARED_LIBRARYIS_COMMONset trust-readonly-sections onThe default is off.
set trust-readonly-sections offAll file-specifying commands allow both absolute and relative file names as arguments. gdb always converts the file name to an absolute file name and remembers it that way.
gdb supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared libraries.
gdb automatically loads symbol definitions from shared libraries
when you use the run command, or when you examine a core file.
(Before you issue the run command, gdb does not understand
references to a function in a shared library, however—unless you are
debugging a core file).
On HP-UX, if the program loads a library explicitly, gdb
automatically loads the symbols at the time of the shl_load call.
There are times, however, when you may wish to not automatically load symbol definitions from shared libraries, such as when they are particularly large or there are many of them.
To control the automatic loading of shared library symbols, use the commands:
set auto-solib-add modeon, symbols from all shared object libraries
will be loaded automatically when the inferior begins execution, you
attach to an independently started inferior, or when the dynamic linker
informs gdb that a new library has been loaded. If mode
is off, symbols must be loaded manually, using the
sharedlibrary command. The default value is on.
show auto-solib-addTo explicitly load shared library symbols, use the sharedlibrary
command:
info shareinfo sharedlibrarysharedlibrary regexshare regexrun. If
regex is omitted all shared libraries required by your program are
loaded.
On some systems, such as HP-UX systems, gdb supports autoloading shared library symbols until a limiting threshold size is reached. This provides the benefit of allowing autoloading to remain on by default, but avoids autoloading excessively large shared libraries, up to a threshold that is initially set, but which you can modify if you wish.
Beyond that threshold, symbols from shared libraries must be explicitly
loaded. To load these symbols, use the command sharedlibrary
filename. The base address of the shared library is determined
automatically by gdb and need not be specified.
To display or set the threshold, use the commands:
set auto-solib-limit thresholdsharedlibrary command. The default threshold is 100 (i.e. 100
Mb).
show auto-solib-limitShared libraries are also supported in many cross or remote debugging configurations. A copy of the target's libraries need to be present on the host system; they need to be the same as the target libraries, although the copies on the target can be stripped as long as the copies on the host are not.
You need to tell gdb where the target libraries are, so that it can load the correct copies—otherwise, it may try to load the host's libraries. gdb has two variables to specify the search directories for target libraries.
set solib-absolute-prefix pathYou can set the default value of `solib-absolute-prefix' by using the configure-time `--with-sysroot' option.
show solib-absolute-prefixset solib-search-path pathshow solib-search-pathgdb allows you to put a program's debugging information in a file separate from the executable itself, in a way that allows gdb to find and load the debugging information automatically. Since debugging information can be very large — sometimes larger than the executable code itself — some systems distribute debugging information for their executables in separate files, which users can install only when they need to debug a problem.
If an executable's debugging information has been extracted to a separate file, the executable should contain a debug link giving the name of the debugging information file (with no directory components), and a checksum of its contents. (The exact form of a debug link is described below.) If the full name of the directory containing the executable is execdir, and the executable has a debug link that specifies the name debugfile, then gdb will automatically search for the debugging information file in three places:
So, for example, if you ask gdb to debug /usr/bin/ls, which has a link containing the name ls.debug, and the global debug directory is /usr/lib/debug, then gdb will look for debug information in /usr/bin/ls.debug, /usr/bin/.debug/ls.debug, and /usr/lib/debug/usr/bin/ls.debug.
You can set the global debugging info directory's name, and view the name gdb is currently using.
set debug-file-directory directoryshow debug-file-directoryA debug link is a special section of the executable file named
.gnu_debuglink. The section must contain:
Any executable file format can carry a debug link, as long as it can
contain a section named .gnu_debuglink with the contents
described above.
The debugging information file itself should be an ordinary
executable, containing a full set of linker symbols, sections, and
debugging information. The sections of the debugging information file
should have the same names, addresses and sizes as the original file,
but they need not contain any data — much like a .bss section
in an ordinary executable.
As of December 2002, there is no standard GNU utility to produce
separated executable / debugging information file pairs. Ulrich
Drepper's elfutils package, starting with version 0.53,
contains a version of the strip command such that the command
strip foo -f foo.debug removes the debugging information from
the executable file foo, places it in the file
foo.debug, and leaves behind a debug link in foo.
Since there are many different ways to compute CRC's (different
polynomials, reversals, byte ordering, etc.), the simplest way to
describe the CRC used in .gnu_debuglink sections is to give the
complete code for a function that computes it:
unsigned long
gnu_debuglink_crc32 (unsigned long crc,
unsigned char *buf, size_t len)
{
static const unsigned long crc32_table[256] =
{
0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
0x2d02ef8d
};
unsigned char *end;
crc = ~crc & 0xffffffff;
for (end = buf + len; buf < end; ++buf)
crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
return ~crc & 0xffffffff;
}
While reading a symbol file, gdb occasionally encounters problems,
such as symbol types it does not recognize, or known bugs in compiler
output. By default, gdb does not notify you of such problems, since
they are relatively common and primarily of interest to people
debugging compilers. If you are interested in seeing information
about ill-constructed symbol tables, you can either ask gdb to print
only one message about each such type of problem, no matter how many
times the problem occurs; or you can ask gdb to print more messages,
to see how many times the problems occur, with the set
complaints command (see Optional warnings and messages).
The messages currently printed, and their meanings, include:
inner block not inside outer block in symbolgdb circumvents the problem by treating the inner block as if it had
the same scope as the outer block. In the error message, symbol
may be shown as “(don't know)” if the outer block is not a
function.
block at address out of ordergdb does not circumvent this problem, and has trouble
locating symbols in the source file whose symbols it is reading. (You
can often determine what source file is affected by specifying
set verbose on. See Optional warnings and messages.)
bad block start address patchedgdb circumvents the problem by treating the symbol scope block as
starting on the previous source line.
bad string table offset in symbol ngdb circumvents the problem by considering the symbol to have the
name foo, which may cause other problems if many symbols end up
with this name.
unknown symbol type 0xnn0xnn is the symbol type of the
uncomprehended information, in hexadecimal.
gdb circumvents the error by ignoring this symbol information.
This usually allows you to debug your program, though certain symbols
are not accessible. If you encounter such a problem and feel like
debugging it, you can debug gdb with itself, breakpoint
on complain, then go up to the function read_dbx_symtab
and examine *bufp to see the symbol.
stub type has NULL nameconst/volatile indicator missing (ok if using g++ v1.x), got...info mismatch between compiler and debuggerA target is the execution environment occupied by your program.
Often, gdb runs in the same host environment as your program;
in that case, the debugging target is specified as a side effect when
you use the file or core commands. When you need more
flexibility—for example, running gdb on a physically separate
host, or controlling a standalone system over a serial port or a
realtime system over a TCP/IP connection—you can use the target
command to specify one of the target types configured for gdb
(see Commands for managing targets).
There are three classes of targets: processes, core files, and executable files. gdb can work concurrently on up to three active targets, one in each class. This allows you to (for example) start a process and inspect its activity without abandoning your work on a core file.
For example, if you execute `gdb a.out', then the executable file
a.out is the only active target. If you designate a core file as
well—presumably from a prior run that crashed and coredumped—then
gdb has two active targets and uses them in tandem, looking
first in the corefile target, then in the executable file, to satisfy
requests for memory addresses. (Typically, these two classes of target
are complementary, since core files contain only a program's
read-write memory—variables and so on—plus machine status, while
executable files contain only the program text and initialized data.)
When you type run, your executable file becomes an active process
target as well. When a process target is active, all gdb
commands requesting memory addresses refer to that target; addresses in
an active core file or executable file target are obscured while the
process target is active.
Use the core-file and exec-file commands to select a new
core file or executable target (see Commands to specify files). To specify as a target a process that is already running, use
the attach command (see Debugging an already-running process).
target type parametersFurther parameters are interpreted by the target protocol, but typically include things like device names or host names to connect with, process numbers, and baud rates.
The target command does not repeat if you press <RET> again
after executing the command.
help targetinfo target or info files
(see Commands to specify files).
help target nameset gnutarget argsset gnutarget command. Unlike most target commands,
with gnutarget the target refers to a program, not a machine.
Warning: To specify a file format with set gnutarget,
you must know the actual BFD name.
show gnutargetshow gnutarget command to display what file format
gnutarget is set to read. If you have not set gnutarget,
gdb will determine the file format for each file automatically,
and show gnutarget displays `The current BDF target is "auto"'.
Here are some common targets (available, or not, depending on the GDB configuration):
target exec programtarget core filenametarget remote devtarget remote
supports the load command. This is only useful if you have
some other way of getting the stub to the target system, and you can put
it somewhere in memory where it won't get clobbered by the download.
target sim target sim
load
run
works; however, you cannot assume that a specific memory map, device drivers, or even basic I/O is available, although some simulators do provide these. For info about any processor-specific simulator details, see the appropriate section in Embedded Processors.
Some configurations may include these targets as well:
target nrom devDifferent targets are available on different configurations of gdb; your configuration may have more or fewer targets.
Many remote targets require you to download the executable's code once you've successfully established a connection.
load filenameload command may be available. Where it exists, it
is meant to make filename (an executable) available for debugging
on the remote system—by downloading, or dynamic linking, for example.
load also records the filename symbol table in gdb, like
the add-symbol-file command.
If your gdb does not have a load command, attempting to
execute it gets the error message “You can't do that when your
target is ...”
The file is loaded at whatever address is specified in the executable. For some object file formats, you can specify the load address when you link the program; for other formats, like a.out, the object file format specifies a fixed address.
load does not repeat if you press <RET> again after using it.
Some types of processors, such as the MIPS, PowerPC, and Renesas SH, offer the ability to run either big-endian or little-endian byte orders. Usually the executable or symbol will include a bit to designate the endian-ness, and you will not need to worry about which to use. However, you may still find it useful to adjust gdb's idea of processor endian-ness manually.
set endian bigset endian littleset endian autoshow endianNote that these commands merely adjust interpretation of symbolic data on the host, and that they have absolutely no effect on the target system.
If you are trying to debug a program running on a machine that cannot run gdb in the usual way, it is often useful to use remote debugging. For example, you might use remote debugging on an operating system kernel, or on a small system which does not have a general purpose operating system powerful enough to run a full-featured debugger.
Some configurations of gdb have special serial or TCP/IP interfaces to make this work with particular debugging targets. In addition, gdb comes with a generic serial protocol (specific to gdb, but not specific to any particular target system) which you can use if you write the remote stubs—the code that runs on the remote system to communicate with gdb.
Other remote targets may be available in your
configuration of gdb; use help target to list them.
Some targets support kernel object display. Using this facility, gdb communicates specially with the underlying operating system and can display information about operating system-level objects such as mutexes and other synchronization objects. Exactly which objects can be displayed is determined on a per-OS basis.
Use the set os command to set the operating system. This tells
gdb which kernel object display module to initialize:
(gdb) set os cisco
The associated command show os displays the operating system
set with the set os command; if no operating system has been
set, show os will display an empty string `""'.
If set os succeeds, gdb will display some information
about the operating system, and will create a new info command
which can be used to query the target. The info command is named
after the operating system:
(gdb) info cisco
List of Cisco Kernel Objects
Object Description
any Any and all objects
Further subcommands can be used to query about particular objects known by the kernel.
There is currently no way to determine whether a given operating system is supported other than to try setting it with set os name, where name is the name of the operating system you want to try.
On the gdb host machine, you will need an unstripped copy of your program, since gdb needs symobl and debugging information. Start up gdb as usual, using the name of the local copy of your program as the first argument.
If you're using a serial line, you may want to give gdb the
`--baud' option, or use the set remotebaud command
before the target command.
After that, use target remote to establish communications with
the target machine. Its argument specifies how to communicate—either
via a devicename attached to a direct serial line, or a TCP or UDP port
(possibly to a terminal server which in turn has a serial line to the
target). For example, to use a serial line connected to the device
named /dev/ttyb:
target remote /dev/ttyb
To use a TCP connection, use an argument of the form
host:port or tcp:host:port.
For example, to connect to port 2828 on a
terminal server named manyfarms:
target remote manyfarms:2828
If your remote target is actually running on the same machine as your debugger session (e.g. a simulator of your target running on the same host), you can omit the hostname. For example, to connect to port 1234 on your local machine:
target remote :1234
Note that the colon is still required here.
To use a UDP connection, use an argument of the form
udp:host:port. For example, to connect to UDP port 2828
on a terminal server named manyfarms:
target remote udp:manyfarms:2828
When using a UDP connection for remote debugging, you should keep in mind that the `U' stands for “Unreliable”. UDP can silently drop packets on busy or unreliable networks, which will cause havoc with your debugging session.
Now you can use all the usual commands to examine and change data and to step and continue the remote program.
Whenever gdb is waiting for the remote program, if you type the interrupt character (often <C-C>), gdb attempts to stop the program. This may or may not succeed, depending in part on the hardware and the serial drivers the remote system uses. If you type the interrupt character once again, gdb displays this prompt:
Interrupted while waiting for the program.
Give up (and stop debugging it)? (y or n)
If you type y, gdb abandons the remote debugging session. (If you decide you want to try again later, you can use `target remote' again to connect once more.) If you type n, gdb goes back to waiting.
detachdetach command to release it from gdb control.
Detaching from the target normally resumes its execution, but the results
will depend on your particular remote stub. After the detach
command, gdb is free to connect to another target.
disconnectdisconnect command behaves like detach, except that
the target is generally not resumed. It will wait for gdb
(this instance or another one) to connect and continue debugging. After
the disconnect command, gdb is again free to connect to
another target.
gdbserver programgdbserver is a control program for Unix-like systems, which
allows you to connect your program with a remote gdb via
target remote—but without linking in the usual debugging stub.
gdbserver is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that gdb itself does. In fact, a system that can run
gdbserver to connect to a remote gdb could also run
gdb locally! gdbserver is sometimes useful nevertheless,
because it is a much smaller program than gdb itself. It is
also easier to port than all of gdb, so you may be able to get
started more quickly on a new system by using gdbserver.
Finally, if you develop code for real-time systems, you may find that
the tradeoffs involved in real-time operation make it more convenient to
do as much development work as possible on another system, for example
by cross-compiling. You can use gdbserver to make a similar
choice for debugging.
gdb and gdbserver communicate via either a serial line
or a TCP connection, using the standard gdb remote serial
protocol.
gdbserver does not need your program's symbol table, so you can
strip the program if necessary to save space. gdb on the host
system does all the symbol handling.
To use the server, you must tell it how to communicate with gdb; the name of your program; and the arguments for your program. The usual syntax is:
target> gdbserver comm program [ args ... ]
comm is either a device name (to use a serial line) or a TCP hostname and portnumber. For example, to debug Emacs with the argument `foo.txt' and communicate with gdb over the serial port /dev/com1:
target> gdbserver /dev/com1 emacs foo.txt
gdbserver waits passively for the host gdb to communicate
with it.
To use a TCP connection instead of a serial line:
target> gdbserver host:2345 emacs foo.txt
The only difference from the previous example is the first argument,
specifying that you are communicating with the host gdb via
TCP. The `host:2345' argument means that gdbserver is to
expect a TCP connection from machine `host' to local TCP port 2345.
(Currently, the `host' part is ignored.) You can choose any number
you want for the port number as long as it does not conflict with any
TCP ports already in use on the target system (for example, 23 is
reserved for telnet).5 You must use the same port number with the host gdb
target remote command.
On some targets, gdbserver can also attach to running programs.
This is accomplished via the --attach argument. The syntax is:
target> gdbserver comm --attach pid
pid is the process ID of a currently running process. It isn't necessary
to point gdbserver at a binary for the running process.
You can debug processes by name instead of process ID if your target has the
pidof utility:
target> gdbserver comm --attach `pidof PROGRAM`
In case more than one copy of PROGRAM is running, or PROGRAM
has multiple threads, most versions of pidof support the
-s option to only return the first process ID.
gdbserver prior to using
the target remote command. Otherwise you may get an error whose
text depends on the host system, but which usually looks something like
`Connection refused'. You don't need to use the load
command in gdb when using gdbserver, since the program is
already on the target.
gdbserve.nlm programgdbserve.nlm is a control program for NetWare systems, which
allows you to connect your program with a remote gdb via
target remote.
gdb and gdbserve.nlm communicate via a serial line,
using the standard gdb remote serial protocol.
gdbserve.nlm does not need your program's symbol table, so you
can strip the program if necessary to save space. gdb on the
host system does all the symbol handling.
To use the server, you must tell it how to communicate with gdb; the name of your program; and the arguments for your program. The syntax is:
load gdbserve [ BOARD=board ] [ PORT=port ]
[ BAUD=baud ] program [ args ... ]
board and port specify the serial line; baud specifies the baud rate used by the connection. port and node default to 0, baud defaults to 9600bps.
For example, to debug Emacs with the argument `foo.txt'and communicate with gdb over serial port number 2 or board 1 using a 19200bps connection:
load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
The following configuration options are available when debugging remote programs:
set remote hardware-watchpoint-limit limitset remote hardware-breakpoint-limit limitThe stub files provided with gdb implement the target side of the communication protocol, and the gdb side is implemented in the gdb source file remote.c. Normally, you can simply allow these subroutines to communicate, and ignore the details. (If you're implementing your own stub file, you can still ignore the details: start with one of the existing stub files. sparc-stub.c is the best organized, and therefore the easiest to read.)
To debug a program running on another machine (the debugging target machine), you must first arrange for all the usual prerequisites for the program to run by itself. For example, for a C program, you need:
The next step is to arrange for your program to use a serial port to communicate with the machine where gdb is running (the host machine). In general terms, the scheme looks like this:
On certain remote targets, you can use an auxiliary program
gdbserver instead of linking a stub into your program.
See Using the gdbserver program, for details.
The debugging stub is specific to the architecture of the remote machine; for example, use sparc-stub.c to debug programs on sparc boards.
These working remote stubs are distributed with gdb:
i386-stub.cm68k-stub.csh-stub.csparc-stub.csparcl-stub.cThe README file in the gdb distribution may list other recently added stubs.
The debugging stub for your architecture supplies these three subroutines:
set_debug_trapshandle_exception to run when your
program stops. You must call this subroutine explicitly near the
beginning of your program.
handle_exceptionhandle_exception to
run when a trap is triggered.
handle_exception takes control when your program stops during
execution (for example, on a breakpoint), and mediates communications
with gdb on the host machine. This is where the communications
protocol is implemented; handle_exception acts as the gdb
representative on the target machine. It begins by sending summary
information on the state of your program, then continues to execute,
retrieving and transmitting any information gdb needs, until you
execute a gdb command that makes your program resume; at that point,
handle_exception returns control to your own code on the target
machine.
breakpointhandle_exception—in effect, to gdb. On some machines,
simply receiving characters on the serial port may also trigger a trap;
again, in that situation, you don't need to call breakpoint from
your own program—simply running `target remote' from the host
gdb session gets control.
Call breakpoint if none of these is true, or if you simply want
to make certain your program stops at a predetermined point for the
start of your debugging session.
The debugging stubs that come with gdb are set up for a particular chip architecture, but they have no information about the rest of your debugging target machine.
First of all you need to tell the stub how to communicate with the serial port.
int getDebugChar()getchar for your target system; a
different name is used to allow you to distinguish the two if you wish.
void putDebugChar(int)putchar for your target system; a
different name is used to allow you to distinguish the two if you wish.
If you want gdb to be able to stop your program while it is
running, you need to use an interrupt-driven serial driver, and arrange
for it to stop when it receives a ^C (`\003', the control-C
character). That is the character which gdb uses to tell the
remote system to stop.
Getting the debugging target to return the proper status to gdb
probably requires changes to the standard stub; one quick and dirty way
is to just execute a breakpoint instruction (the “dirty” part is that
gdb reports a SIGTRAP instead of a SIGINT).
Other routines you need to supply are:
void exceptionHandler (int exception_number, void *exception_address)For the 386, exception_address should be installed as an interrupt
gate so that interrupts are masked while the handler runs. The gate
should be at privilege level 0 (the most privileged level). The
sparc and 68k stubs are able to mask interrupts themselves without
help from exceptionHandler.
void flush_i_cache()On target machines that have instruction caches, gdb requires this function to make certain that the state of your program is stable.
You must also make sure this library routine is available:
void *memset(void *, int, int)memset that sets an area of
memory to a known value. If you have one of the free versions of
libc.a, memset can be found there; otherwise, you must
either obtain it from your hardware manufacturer, or write your own.
If you do not use the GNU C compiler, you may need other standard
library subroutines as well; this varies from one stub to another,
but in general the stubs are likely to use any of the common library
subroutines which gcc generates as inline code.
In summary, when your program is ready to debug, you must follow these steps.
getDebugChar,putDebugChar,flush_i_cache,memset,exceptionHandler.
set_debug_traps();
breakpoint();
exceptionHook. Normally you just use:
void (*exceptionHook)() = 0;
but if before calling set_debug_traps, you set it to point to a
function in your program, that function is called when
gdb continues after stopping on a trap (for example, bus
error). The function indicated by exceptionHook is called with
one parameter: an int which is the exception number.
While nearly all gdb commands are available for all native and cross versions of the debugger, there are some exceptions. This chapter describes things that are only available in certain configurations.
There are three major categories of configurations: native configurations, where the host and target are the same, embedded operating system configurations, which are usually the same for several different processor architectures, and bare embedded processors, which are quite different from each other.
This section describes details specific to particular native configurations.
On HP-UX systems, if you refer to a function or variable name that begins with a dollar sign, gdb searches for a user or system name first, before it searches for a convenience variable.
Many versions of SVR4 provide a facility called `/proc' that can be
used to examine the image of a running process using file-system
subroutines. If gdb is configured for an operating system with
this facility, the command info proc is available to report on
several kinds of information about the process running your program.
info proc works only on SVR4 systems that include the
procfs code. This includes OSF/1 (Digital Unix), Solaris, Irix,
and Unixware, but not HP-UX or gnu/Linux, for example.
info procinfo proc mappingsdjgpp is the port of gnu development tools to MS-DOS and MS-Windows. djgpp programs are 32-bit protected-mode programs that use the DPMI (DOS Protected-Mode Interface) API to run on top of real-mode DOS systems and their emulations.
gdb supports native debugging of djgpp programs, and defines a few commands specific to the djgpp port. This subsection describes those commands.
info dosinfo dos sysinfoinfo dos gdtinfo dos ldtinfo dos idtA typical djgpp program uses 3 segments: a code segment, a data segment (used for both data and the stack), and a DOS segment (which allows access to DOS/BIOS data structures and absolute addresses in conventional memory). However, the DPMI host will usually define additional segments in order to support the DPMI environment.
These commands allow to display entries from the descriptor tables. Without an argument, all entries from the specified table are displayed. An argument, which should be an integer expression, means display a single entry whose index is given by the argument. For example, here's a convenient way to display information about the debugged program's data segment:
(gdb) info dos ldt $ds
0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
This comes in handy when you want to see whether a pointer is outside the data segment's limit (i.e. garbled).
info dos pdeinfo dos pteWithout an argument, info dos pde displays the entire Page Directory, and info dos pte displays all the entries in all of the Page Tables. An argument, an integer expression, given to the info dos pde command means display only that entry from the Page Directory table. An argument given to the info dos pte command means display entries from a single Page Table, the one pointed to by the specified entry in the Page Directory.
These commands are useful when your program uses DMA (Direct Memory Access), which needs physical addresses to program the DMA controller.
These commands are supported only with some DPMI servers.
info dos address-pte addri is stored:
(gdb) info dos address-pte __djgpp_base_address + (char *)&i
Page Table entry for address 0x11a00d30:
Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
This says that i is stored at offset 0xd30 from the page
whose physical base address is 0x02698000, and prints all the
attributes of that page.
Note that you must cast the addresses of variables to a char *,
since otherwise the value of __djgpp_base_address, the base
address of all variables and functions in a djgpp program, will
be added using the rules of C pointer arithmetics: if i is
declared an int, gdb will add 4 times the value of
__djgpp_base_address to the address of i.
Here's another example, it displays the Page Table entry for the transfer buffer:
(gdb) info dos address-pte *((unsigned *)&_go32_info_block + 3)
Page Table entry for address 0x29110:
Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
(The + 3 offset is because the transfer buffer's address is the
3rd member of the _go32_info_block structure.) The output of
this command clearly shows that addresses in conventional memory are
mapped 1:1, i.e. the physical and linear addresses are identical.
This command is supported only with some DPMI servers.
gdb supports native debugging of MS Windows programs, including DLLs with and without symbolic debugging information. There are various additional Cygwin-specific commands, described in this subsection. The subsubsection see Non-debug DLL symbols describes working with DLLs that have no debugging symbols.
info w32info w32 selectorGetThreadSelectorEntry function.
It takes an optional argument that is evaluated to
a long value to give the information about this given selector.
Without argument, this command displays information
about the the six segment registers.
info dlldll-symbolsset new-console modeon the debuggee will
be started in a new console on next start.
If mode is offi, the debuggee will
be started in the same console as the debugger.
show new-consoleset new-group modeshow new-groupset debugeventsset debugexecset debugexceptionsset debugmemoryset shellshow shellVery often on windows, some of the DLLs that your program relies on do not include symbolic debugging information (for example, kernel32.dll). When gdb doesn't recognize any debugging symbols in a DLL, it relies on the minimal amount of symbolic information contained in the DLL's export table. This subsubsection describes working with such symbols, known internally to gdb as “minimal symbols”.
Note that before the debugged program has started execution, no DLLs
will have been loaded. The easiest way around this problem is simply to
start the program — either by setting a breakpoint or letting the
program run once to completion. It is also possible to force
gdb to load a particular DLL before starting the executable —
see the shared library information in see Files or the
dll-symbols command in see Cygwin Native. Currently,
explicitly loading symbols from a DLL with no debugging information will
cause the symbol names to be duplicated in gdb's lookup table,
which may adversely affect symbol lookup performance.
In keeping with the naming conventions used by the Microsoft debugging
tools, DLL export symbols are made available with a prefix based on the
DLL name, for instance KERNEL32!CreateFileA. The plain name is
also entered into the symbol table, so CreateFileA is often
sufficient. In some cases there will be name clashes within a program
(particularly if the executable itself includes full debugging symbols)
necessitating the use of the fully qualified name when referring to the
contents of the DLL. Use single-quotes around the name to avoid the
exclamation mark (“!”) being interpreted as a language operator.
Note that the internal name of the DLL may be all upper-case, even
though the file name of the DLL is lower-case, or vice-versa. Since
symbols within gdb are case-sensitive this may cause
some confusion. If in doubt, try the info functions and
info variables commands or even maint print msymbols (see
see Symbols). Here's an example:
(gdb) info function CreateFileA
All functions matching regular expression "CreateFileA":
Non-debugging symbols:
0x77e885f4 CreateFileA
0x77e885f4 KERNEL32!CreateFileA
(gdb) info function !
All functions matching regular expression "!":
Non-debugging symbols:
0x6100114c cygwin1!__assert
0x61004034 cygwin1!_dll_crt0@0
0x61004240 cygwin1!dll_crt0(per_process *)
[etc...]
Symbols extracted from a DLL's export table do not contain very much type information. All that gdb can do is guess whether a symbol refers to a function or variable depending on the linker section that contains the symbol. Also note that the actual contents of the memory contained in a DLL are not available unless the program is running. This means that you cannot examine the contents of a variable or disassemble a function within a DLL without a running program.
Variables are generally treated as pointers and dereferenced automatically. For this reason, it is often necessary to prefix a variable name with the address-of operator (“&”) and provide explicit type information in the command. Here's an example of the type of problem:
(gdb) print 'cygwin1!__argv'
$1 = 268572168
(gdb) x 'cygwin1!__argv'
0x10021610: "\230y\""
And two possible solutions:
(gdb) print ((char **)'cygwin1!__argv')[0]
$2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
(gdb) x/2x &'cygwin1!__argv'
0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
(gdb) x/x 0x10021608
0x10021608: 0x0022fd98
(gdb) x/s 0x0022fd98
0x22fd98: "/cygdrive/c/mydirectory/myprogram"
Setting a break point within a DLL is possible even before the program starts execution. However, under these circumstances, gdb can't examine the initial instructions of the function in order to skip the function's frame set-up code. You can work around this by using “*&” to set the breakpoint at a raw memory address:
(gdb) break *&'python22!PyOS_Readline'
Breakpoint 1 at 0x1e04eff0
The author of these extensions is not entirely convinced that setting a break point within a shared DLL like kernel32.dll is completely safe.
This section describes configurations involving the debugging of embedded operating systems that are available for several different architectures.
gdb includes the ability to debug programs running on various real-time operating systems.
target vxworks machinenameOn VxWorks, load links filename dynamically on the
current target system as well as adding its symbols in gdb.
gdb enables developers to spawn and debug tasks running on networked
VxWorks targets from a Unix host. Already-running tasks spawned from
the VxWorks shell can also be debugged. gdb uses code that runs on
both the Unix host and on the VxWorks target. The program
gdb is installed and executed on the Unix host. (It may be
installed with the name vxgdb, to distinguish it from a
gdb for debugging programs on the host itself.)
VxWorks-timeout argsvxworks-timeout.
This option is set by the user, and args represents the number of
seconds gdb waits for responses to rpc's. You might use this if
your VxWorks target is a slow software simulator or is on the far side
of a thin network line.
The following information on connecting to VxWorks was current when this manual was produced; newer releases of VxWorks may use revised procedures.
To use gdb with VxWorks, you must rebuild your VxWorks kernel
to include the remote debugging interface routines in the VxWorks
library rdb.a. To do this, define INCLUDE_RDB in the
VxWorks configuration file configAll.h and rebuild your VxWorks
kernel. The resulting kernel contains rdb.a, and spawns the
source debugging task tRdbTask when VxWorks is booted. For more
information on configuring and remaking VxWorks, see the manufacturer's
manual.
Once you have included rdb.a in your VxWorks system image and set
your Unix execution search path to find gdb, you are ready to
run gdb. From your Unix host, run gdb (or
vxgdb, depending on your installation).
gdb comes up showing the prompt:
(vxgdb)
The gdb command target lets you connect to a VxWorks target on the
network. To connect to a target whose host name is “tt”, type:
(vxgdb) target vxworks tt
gdb displays messages like these:
Attaching remote machine across net...
Connected to tt.
gdb then attempts to read the symbol tables of any object modules loaded into the VxWorks target since it was last booted. gdb locates these files by searching the directories listed in the command search path (see Your program's environment); if it fails to find an object file, it displays a message such as:
prog.o: No such file or directory.
When this happens, add the appropriate directory to the search path with
the gdb command path, and execute the target
command again.
If you have connected to the VxWorks target and you want to debug an
object that has not yet been loaded, you can use the gdb
load command to download a file from Unix to VxWorks
incrementally. The object file given as an argument to the load
command is actually opened twice: first by the VxWorks target in order
to download the code, then by gdb in order to read the symbol
table. This can lead to problems if the current working directories on
the two systems differ. If both systems have NFS mounted the same
filesystems, you can avoid these problems by using absolute paths.
Otherwise, it is simplest to set the working directory on both systems
to the directory in which the object file resides, and then to reference
the file by its name, without any path. For instance, a program
prog.o may reside in vxpath/vw/demo/rdb in VxWorks
and in hostpath/vw/demo/rdb on the host. To load this
program, type this on VxWorks:
-> cd "vxpath/vw/demo/rdb"
Then, in gdb, type:
(vxgdb) cd hostpath/vw/demo/rdb
(vxgdb) load prog.o
gdb displays a response similar to this:
Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
You can also use the load command to reload an object module
after editing and recompiling the corresponding source file. Note that
this makes gdb delete all currently-defined breakpoints,
auto-displays, and convenience variables, and to clear the value
history. (This is necessary in order to preserve the integrity of
debugger's data structures that reference the target system's symbol
table.)
You can also attach to an existing task using the attach command as
follows:
(vxgdb) attach task
where task is the VxWorks hexadecimal task ID. The task can be running or suspended when you attach to it. Running tasks are suspended at the time of attachment.
This section goes into details specific to particular embedded configurations.
target rdi devtarget rdp devtarget hms devdevice and speed to control the serial
line and the communications speed used.
target e7000 devtarget sh3 devtarget sh3e devWhen you select remote debugging to a Renesas SH, H8/300, or H8/500
board, the load command downloads your program to the Renesas
board and also opens it as the current executable target for
gdb on your host (like the file command).
gdb needs to know these things to talk to your Renesas SH, H8/300, or H8/500:
Use the special gdb command `device port' if you need to explicitly set the serial device. The default port is the first available port on your host. This is only necessary on Unix hosts, where it is typically something like /dev/ttya.
gdb has another special command to set the communications
speed: `speed bps'. This command also is only used from Unix
hosts; on DOS hosts, set the line speed as usual from outside gdb with
the DOS mode command (for instance,
mode com2:9600,n,8,1,p for a 9600bps connection).
The `device' and `speed' commands are available only when you
use a Unix host to debug your Renesas microprocessor programs. If you
use a DOS host,
gdb depends on an auxiliary terminate-and-stay-resident program
called asynctsr to communicate with the development board
through a PC serial port. You must also use the DOS mode command
to set up the serial port on the DOS side.
The following sample session illustrates the steps needed to start a program under gdb control on an H8/300. The example uses a sample H8/300 program called t.x. The procedure is the same for the Renesas SH and the H8/500.
First hook up your development board. In this example, we use a
board attached to serial port COM2; if you use a different serial
port, substitute its name in the argument of the mode command.
When you call asynctsr, the auxiliary comms program used by the
debugger, you give it just the numeric part of the serial port's name;
for example, `asyncstr 2' below runs asyncstr on
COM2.
C:\H8300\TEST> asynctsr 2
C:\H8300\TEST> mode com2:9600,n,8,1,p
Resident portion of MODE loaded
COM2: 9600, n, 8, 1, p
Warning: We have noticed a bug in PC-NFS that conflicts withasynctsr. If you also run PC-NFS on your DOS host, you may need to disable it, or even boot without it, to useasynctsrto control your development board.
Now that serial communications are set up, and the development board is
connected, you can start up gdb. Call gdb with
the name of your program as the argument. gdb prompts
you, as usual, with the prompt `(gdb)'. Use two special
commands to begin your debugging session: `target hms' to specify
cross-debugging to the Renesas board, and the load command to
download your program to the board. load displays the names of
the program's sections, and a `*' for each 2K of data downloaded.
(If you want to refresh gdb data on symbols or on the
executable file without downloading, use the gdb commands
file or symbol-file. These commands, and load
itself, are described in Commands to specify files.)
(eg-C:\H8300\TEST) gdb t.x
gdb is free software and you are welcome to distribute copies
of it under certain conditions; type "show copying" to see
the conditions.
There is absolutely no warranty for gdb; type "show warranty"
for details.
gdb 6.1, Copyright 1992 Free Software Foundation, Inc...
(gdb) target hms
Connected to remote H8/300 HMS system.
(gdb) load t.x
.text : 0x8000 .. 0xabde ***********
.data : 0xabde .. 0xad30 *
.stack : 0xf000 .. 0xf014 *
At this point, you're ready to run or debug your program. From here on,
you can use all the usual gdb commands. The break command
sets breakpoints; the run command starts your program;
print or x display data; the continue command
resumes execution after stopping at a breakpoint. You can use the
help command at any time to find out more about gdb commands.
Remember, however, that operating system facilities aren't available on your development board; for example, if your program hangs, you can't send an interrupt—but you can press the reset switch!
Use the reset button on the development board
In either case, gdb sees the effect of a reset on the development board as a “normal exit” of your program.
You can use the E7000 in-circuit emulator to develop code for either the Renesas SH or the H8/300H. Use one of these forms of the `target e7000' command to connect gdb to your E7000:
target e7000 port speedtarget e7000 hostnametelnet to connect.
Some gdb commands are available only for the H8/300:
set machine h8300set machine h8300hset memory modshow memorysmall,
big, medium, and compact.
target m32r devtarget m32rsdi devThe Motorola m68k configuration includes ColdFire support, and target command for the following ROM monitors.
target abug devtarget cpu32bug devtarget dbug devtarget est devtarget rom68k devtarget rombug devgdb can use the MIPS remote debugging protocol to talk to a MIPS board attached to a serial line. This is available when you configure gdb with `--target=mips-idt-ecoff'.
Use these gdb commands to specify the connection to your target board:
target mips portgdb with the
name of your program as the argument. To connect to the board, use the
command `target mips port', where port is the name of
the serial port connected to the board. If the program has not already
been downloaded to the board, you may use the load command to
download it. You can then use all the usual gdb commands.
For example, this sequence connects to the target board through a serial port, and loads and runs a program called prog through the debugger:
host$ gdb prog
gdb is free software and ...
(gdb) target mips /dev/ttyb
(gdb) load prog
(gdb) run
target mips hostname:portnumbertarget pmon porttarget ddb porttarget lsi porttarget r3900 devtarget array devgdb also supports these special commands for MIPS targets:
set processor argsshow processorset processor command to set the type of MIPS
processor when you want to access processor-type-specific registers.
For example, set processor r3041 tells gdb
to use the CPU registers appropriate for the 3041 chip.
Use the show processor command to see what MIPS processor gdb
is using. Use the info reg command to see what registers
gdb is using.
set mipsfpu doubleset mipsfpu singleset mipsfpu noneshow mipsfpuIn previous versions the only choices were double precision or no floating point, so `set mipsfpu on' will select double precision and `set mipsfpu off' will select no floating point.
As usual, you can inquire about the mipsfpu variable with
`show mipsfpu'.
set remotedebug nshow remotedebugremotedebug variable. If you set it to 1 using
`set remotedebug 1', every packet is displayed. If you set it
to 2, every character is displayed. You can check the current value
at any time with the command `show remotedebug'.
set timeout secondsset retransmit-timeout secondsshow timeoutshow retransmit-timeoutset timeout seconds command. The
default is 5 seconds. Similarly, you can control the timeout used while
waiting for an acknowledgement of a packet with the set
retransmit-timeout seconds command. The default is 3 seconds.
You can inspect both values with show timeout and show
retransmit-timeout. (These commands are only available when
gdb is configured for `--target=mips-idt-ecoff'.)
The timeout set by set timeout does not apply when gdb
is waiting for your program to stop. In that case, gdb waits
forever because it has no way of knowing how long the program is going
to run before stopping.
See OR1k Architecture document (www.opencores.org) for more information about platform and commands.
target jtag jtag://host:portExample: target jtag jtag://localhost:9999
or1ksim commandor1ksim OpenRISC 1000 Architectural
Simulator, proprietary commands can be executed.
info or1k sprinfo or1k spr groupinfo or1k spr groupnoinfo or1k spr group registerinfo or1k spr registerinfo or1k spr groupno registernoinfo or1k spr registernospr group register valuespr register valuespr groupno registerno valuespr registerno valueSome implementations of OpenRISC 1000 Architecture also have hardware trace. It is very similar to gdb trace, except it does not interfere with normal program execution and is thus much faster. Hardware breakpoints/watchpoint triggers can be set using:
$LEA/$LDATA$SEA/$SDATA$AEA/$ADATA$FETCHWhen triggered, it can capture low level data, like: PC, LSEA,
LDATA, SDATA, READSPR, WRITESPR, INSTR.
hwatch conditionalhwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)
hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)
htrace infohtrace trigger conditionalhtrace qualifier conditionalhtrace stop conditionalhtrace record [data]*htrace enablehtrace disablehtrace rewind [filename]If filename is specified, new trace file is made and any newly collected data will be written there.
htrace print [start [len]]htrace mode continuoushtrace mode suspendtarget dink32 devtarget ppcbug devtarget ppcbug1 devtarget sds devtarget op50n devtarget w89k devtarget hms devdevice and speed to control the serial line and
the communications speed used.
target e7000 devtarget sh3 devtarget sh3e dev
gdb enables developers to debug tasks running on
Sparclet targets from a Unix host.
gdb uses code that runs on
both the Unix host and on the Sparclet target. The program
gdb is installed and executed on the Unix host.
remotetimeout argsremotetimeout.
This option is set by the user, and args represents the number of
seconds gdb waits for responses.
When compiling for debugging, include the options `-g' to get debug information and `-Ttext' to relocate the program to where you wish to load it on the target. You may also want to add the options `-n' or `-N' in order to reduce the size of the sections. Example:
sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
You can use objdump to verify that the addresses are what you intended:
sparclet-aout-objdump --headers --syms prog
Once you have set
your Unix execution search path to find gdb, you are ready to
run gdb. From your Unix host, run gdb
(or sparclet-aout-gdb, depending on your installation).
gdb comes up showing the prompt:
(gdbslet)
The gdb command file lets you choose with program to debug.
(gdbslet) file prog
gdb then attempts to read the symbol table of prog. gdb locates the file by searching the directories listed in the command search path. If the file was compiled with debug information (option "-g"), source files will be searched as well. gdb locates the source files by searching the directories listed in the directory search path (see Your program's environment). If it fails to find a file, it displays a message such as:
prog: No such file or directory.
When this happens, add the appropriate directories to the search paths with
the gdb commands path and dir, and execute the
target command again.
The gdb command target lets you connect to a Sparclet target.
To connect to a target on serial port “ttya”, type:
(gdbslet) target sparclet /dev/ttya
Remote target sparclet connected to /dev/ttya
main () at ../prog.c:3
gdb displays messages like these:
Connected to ttya.
Once connected to the Sparclet target,
you can use the gdb
load command to download the file from the host to the target.
The file name and load offset should be given as arguments to the load
command.
Since the file format is aout, the program must be loaded to the starting
address. You can use objdump to find out what this value is. The load
offset is an offset which is added to the VMA (virtual memory address)
of each of the file's sections.
For instance, if the program
prog was linked to text address 0x1201000, with data at 0x12010160
and bss at 0x12010170, in gdb, type:
(gdbslet) load prog 0x12010000
Loading section .text, size 0xdb0 vma 0x12010000
If the code is loaded at a different address then what the program was linked
to, you may need to use the section and add-symbol-file commands
to tell gdb where to map the symbol table.
You can now begin debugging the task using gdb's execution control
commands, b, step, run, etc. See the gdb
manual for the list of commands.
(gdbslet) b main
Breakpoint 1 at 0x12010000: file prog.c, line 3.
(gdbslet) run
Starting program: prog
Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
3 char *symarg = 0;
(gdbslet) step
4 char *execarg = "hello!";
(gdbslet)
target sparclite devgdb may be used with a Tandem ST2000 phone switch, running Tandem's STDBUG protocol.
To connect your ST2000 to the host system, see the manufacturer's manual. Once the ST2000 is physically attached, you can run:
target st2000 dev speed
to establish it as your debugging environment. dev is normally
the name of a serial device, such as /dev/ttya, connected to the
ST2000 via a serial line. You can instead specify dev as a TCP
connection (for example, to a serial line attached via a terminal
concentrator) using the syntax hostname:portnumber.
The load and attach commands are not defined for
this target; you must load your program into the ST2000 as you normally
would for standalone operation. gdb reads debugging information
(such as symbols) from a separate, debugging version of the program
available on your host computer.
These auxiliary gdb commands are available to help you with the ST2000 environment:
st2000 commandconnectWhen configured for debugging Zilog Z8000 targets, gdb includes a Z8000 simulator.
For the Z8000 family, `target sim' simulates either the Z8002 (the unsegmented variant of the Z8000 architecture) or the Z8001 (the segmented variant). The simulator recognizes which architecture is appropriate by inspecting the object code.
target sim argsAfter specifying this target, you can debug programs for the simulated
CPU in the same style as programs for your host computer; use the
file command to load a new program image, the run command
to run your program, and so on.
As well as making available all the usual machine registers (see Registers), the Z8000 simulator provides three additional items of information as specially named registers:
cyclesinststimeYou can refer to these values in gdb expressions with the usual conventions; for example, `b fputc if $cycles>5000' sets a conditional breakpoint that suspends only after at least 5000 simulated clock ticks.
This section describes characteristics of architectures that affect all uses of gdb with the architecture, both native and cross.
set rstack_high_address addressset rstack_high_address command. The argument should be an
address, which you probably want to precede with `0x' to specify in
hexadecimal.
show rstack_high_addressSee the following section.
Alpha- and MIPS-based computers use an unusual stack frame, which sometimes requires gdb to search backward in the object code to find the beginning of a function.
To improve response time (especially for embedded applications, where gdb may be restricted to a slow serial line for this search) you may want to limit the size of this search, using one of these commands:
set heuristic-fence-post limitheuristic-fence-post must search
and therefore the longer it takes to run.
show heuristic-fence-postThese commands are available only when gdb is configured for debugging programs on Alpha or MIPS processors.
You can alter the way gdb interacts with you by using the
set command. For commands controlling how gdb displays
data, see Print settings. Other settings are
described here.
gdb indicates its readiness to read a command by printing a string
called the prompt. This string is normally `(gdb)'. You
can change the prompt string with the set prompt command. For
instance, when debugging gdb with gdb, it is useful to change
the prompt in one of the gdb sessions so that you can always tell
which one you are talking to.
Note: set prompt does not add a space for you after the
prompt you set. This allows you to set a prompt which ends in a space
or a prompt that does not.
set prompt newpromptshow prompt
gdb reads its input commands via the readline interface. This
gnu library provides consistent behavior for programs which provide a
command line interface to the user. Advantages are gnu Emacs-style
or vi-style inline editing of commands, csh-like history
substitution, and a storage and recall of command history across
debugging sessions.
You may control the behavior of command line editing in gdb with the
command set.
set editingset editing onset editing offshow editinggdb can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. Use these commands to manage the gdb command history facility.
set history filename fnameGDBHISTFILE, or to
./.gdb_history (./_gdb_history on MS-DOS) if this variable
is not set.
set history saveset history save onset history filename command. By default, this option is disabled.
set history save offset history size sizeHISTSIZE, or to 256 if this variable is not set.
History expansion assigns special meaning to the character !.
Since ! is also the logical not operator in C, history expansion
is off by default. If you decide to enable history expansion with the
set history expansion on command, you may sometimes need to
follow ! (when it is used as logical not, in an expression) with
a space or a tab to prevent it from being expanded. The readline
history facilities do not attempt substitution on the strings
!= and !(, even when history expansion is enabled.
The commands to control history expansion are:
set history expansion onset history expansionset history expansion offThe readline code comes with more complete documentation of
editing and history expansion features. Users unfamiliar with gnu Emacs
or vi may wish to read it.
show historyshow history filenameshow history saveshow history sizeshow history expansionshow history by itself displays all four states.
show commandsshow commands nshow commands +Certain commands to gdb may produce large amounts of information output to the screen. To help you read all of it, gdb pauses and asks you for input at the end of each page of output. Type <RET> when you want to continue the output, or q to discard the remaining output. Also, the screen width setting determines when to wrap lines of output. Depending on what is being printed, gdb tries to break the line at a readable place, rather than simply letting it overflow onto the following line.
Normally gdb knows the size of the screen from the terminal
driver software. For example, on Unix gdb uses the termcap data base
together with the value of the TERM environment variable and the
stty rows and stty cols settings. If this is not correct,
you can override it with the set height and set
width commands:
set height lppshow heightset width cplshow widthset commands specify a screen height of lpp lines and
a screen width of cpl characters. The associated show
commands display the current settings.
If you specify a height of zero lines, gdb does not pause during output no matter how long the output is. This is useful if output is to a file or to an editor buffer.
Likewise, you can specify `set width 0' to prevent gdb from wrapping its output.
You can always enter numbers in octal, decimal, or hexadecimal in
gdb by the usual conventions: octal numbers begin with
`0', decimal numbers end with `.', and hexadecimal numbers
begin with `0x'. Numbers that begin with none of these are, by
default, entered in base 10; likewise, the default display for
numbers—when no particular format is specified—is base 10. You can
change the default base for both input and output with the set
radix command.
set input-radix base set radix 012
set radix 10.
set radix 0xa
sets the base to decimal. On the other hand, `set radix 10' leaves the radix unchanged no matter what it was.
set output-radix baseshow input-radixshow output-radixgdb can determine the ABI (Application Binary Interface) of your application automatically. However, sometimes you need to override its conclusions. Use these commands to manage gdb's view of the current ABI.
One gdb configuration can debug binaries for multiple operating
system targets, either via remote debugging or native emulation.
gdb will autodetect the OS ABI (Operating System ABI) in use,
but you can override its conclusion using the set osabi command.
One example where this is useful is in debugging of binaries which use
an alternate C library (e.g. uClibc for gnu/Linux) which does
not have the same identifying marks that the standard C library for your
platform provides.
show osabiset osabiset osabi abi
Generally, the way that an argument of type float is passed to a
function depends on whether the function is prototyped. For a prototyped
(i.e. ANSI/ISO style) function, float arguments are passed unchanged,
according to the architecture's convention for float. For unprototyped
(i.e. K&R style) functions, float arguments are first promoted to type
double and then passed.
Unfortunately, some forms of debug information do not reliably indicate whether a function is prototyped. If gdb calls a function that is not marked as prototyped, it consults set coerce-float-to-double.
set coerce-float-to-doubleset coerce-float-to-double onfloat will be promoted to double when passed
to an unprototyped function. This is the default setting.
set coerce-float-to-double offfloat will be passed directly to unprototyped
functions.
gdb needs to know the ABI used for your program's C++
objects. The correct C++ ABI depends on which C++ compiler was
used to build your application. gdb only fully supports
programs with a single C++ ABI; if your program contains code using
multiple C++ ABI's or if gdb can not identify your
program's ABI correctly, you can tell gdb which ABI to use.
Currently supported ABI's include “gnu-v2”, for g++ versions
before 3.0, “gnu-v3”, for g++ versions 3.0 and later, and
“hpaCC” for the HP ANSI C++ compiler. Other C++ compilers may
use the “gnu-v2” or “gnu-v3” ABI's as well. The default setting is
“auto”.
show cp-abiset cp-abiset cp-abi abiset cp-abi autoBy default, gdb is silent about its inner workings. If you are
running on a slow machine, you may want to use the set verbose
command. This makes gdb tell you when it does a lengthy
internal operation, so you will not think it has crashed.
Currently, the messages controlled by set verbose are those
which announce that the symbol table for a source file is being read;
see symbol-file in Commands to specify files.
set verbose onset verbose offshow verboseset verbose is on or off.
By default, if gdb encounters bugs in the symbol table of an object file, it is silent; but if you are debugging a compiler, you may find this information useful (see Errors reading symbol files).
set complaints limitshow complaintsBy default, gdb is cautious, and asks what sometimes seems to be a lot of stupid questions to confirm certain commands. For example, if you try to run a program which is already running:
(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n)
If you are willing to unflinchingly face the consequences of your own commands, you can disable this “feature”:
set confirm offset confirm onshow confirmset debug archshow debug archset debug eventshow debug eventset debug expressionshow debug expressionset debug frameshow debug frameset debug overloadshow debug overloadset debug remoteshow debug remoteset debug serialshow debug serialset debug targetshow debug targetset debug varobjshow debug varobjAside from breakpoint commands (see Breakpoint command lists), gdb provides two ways to store sequences of commands for execution as a unit: user-defined commands and command files.
A user-defined command is a sequence of gdb commands to
which you assign a new name as a command. This is done with the
define command. User commands may accept up to 10 arguments
separated by whitespace. Arguments are accessed within the user command
via $arg0...$arg9. A trivial example:
define adder
print $arg0 + $arg1 + $arg2
To execute the command use:
adder 1 2 3
This defines the command adder, which prints the sum of
its three arguments. Note the arguments are text substitutions, so they may
reference variables, use complex expressions, or even perform inferior
functions calls.
define commandnameThe definition of the command is made up of other gdb command lines,
which are given following the define command. The end of these
commands is marked by a line containing end.
ifelse, followed
by a series of commands that are only executed if the expression
was false. The end of the list is marked by a line containing end.
whileif: the command takes a single argument,
which is an expression to evaluate, and must be followed by the commands to
execute, one per line, terminated by an end.
The commands are executed repeatedly as long as the expression
evaluates to true.
document commandnamehelp. The command commandname must already be
defined. This command reads lines of documentation just as define
reads the lines of the command definition, ending with end.
After the document command is finished, help on command
commandname displays the documentation you have written.
You may use the document command again to change the
documentation of a command. Redefining the command with define
does not change the documentation.
help user-definedshow usershow user commandnameshow max-user-call-depthset max-user-call-depthmax-user-call-depth controls how many recursion
levels are allowed in user-defined commands before GDB suspects an
infinite recursion and aborts the command.
When user-defined commands are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command.
If used interactively, commands that would ask for confirmation proceed without asking when used inside a user-defined command. Many gdb commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.
You may define hooks, which are a special kind of user-defined command. Whenever you run the command `foo', if the user-defined command `hook-foo' exists, it is executed (with no arguments) before that command.
A hook may also be defined which is run after the command you executed. Whenever you run the command `foo', if the user-defined command `hookpost-foo' exists, it is executed (with no arguments) after that command. Post-execution hooks may exist simultaneously with pre-execution hooks, for the same command.
It is valid for a hook to call the command which it hooks. If this occurs, the hook is not re-executed, thereby avoiding infinte recursion.
In addition, a pseudo-command, `stop' exists. Defining (`hook-stop') makes the associated commands execute every time execution stops in your program: before breakpoint commands are run, displays are printed, or the stack frame is printed.
For example, to ignore SIGALRM signals while
single-stepping, but treat them normally during normal execution,
you could define:
define hook-stop
handle SIGALRM nopass
end
define hook-run
handle SIGALRM pass
end
define hook-continue
handle SIGLARM pass
end
As a further example, to hook at the begining and end of the echo
command, and to add extra text to the beginning and end of the message,
you could define:
define hook-echo
echo <<<---
end
define hookpost-echo
echo --->>>\n
end
(gdb) echo Hello World
<<<---Hello World--->>>
(gdb)
You can define a hook for any single-word command in gdb, but
not for command aliases; you should define a hook for the basic command
name, e.g. backtrace rather than bt.
If an error occurs during the execution of your hook, execution of
gdb commands stops and gdb issues a prompt
(before the command that you actually typed had a chance to run).
If you try to define a hook which does not match any known command, you
get a warning from the define command.
A command file for gdb is a file of lines that are gdb commands. Comments (lines starting with #) may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal.
When you start gdb, it automatically executes commands from its init files, normally called .gdbinit6. During startup, gdb does the following:
The init file in your home directory can set options (such as `set complaints') that affect subsequent processing of command line options and operands. Init files are not executed if you use the `-nx' option (see Choosing modes).
On some configurations of gdb, the init file is known by a different name (these are typically environments where a specialized form of gdb may need to coexist with other forms, hence a different name for the specialized version's init file). These are the environments with special init file names:
You can also request the execution of a command file with the
source command:
source filenameThe lines in a command file are executed sequentially. They are not printed as they are executed. An error in any command terminates execution of the command file and control is returned to the console.
Commands that would ask for confirmation if used interactively proceed without asking when used in a command file. Many gdb commands that normally print messages to say what they are doing omit the messages when called from command files.
gdb also accepts command input from standard input. In this mode, normal output goes to standard output and error output goes to standard error. Errors in a command file supplied on standard input do not terminate execution of the command file — execution continues with the next command.
gdb < cmds > log 2>&1
(The syntax above will vary depending on the shell used.) This example will execute commands from the file cmds. All output and errors would be directed to log.
During the execution of a command file or a user-defined command, normal gdb output is suppressed; the only output that appears is what is explicitly printed by the commands in the definition. This section describes three commands useful for generating exactly the output you want.
echo textA backslash at the end of text can be used, as in C, to continue the command onto subsequent lines. For example,
echo This is some text\n\
which is continued\n\
onto several lines.\n
produces the same output as
echo This is some text\n
echo which is continued\n
echo onto several lines.\n
output expressionoutput/fmt expressionprint. See Output formats, for more information.
printf string, expressions... printf (string, expressions...);
For example, you can print two values in hex like this:
printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
The only backslash-escape sequences that you can use in the format string are the simple ones that consist of backslash followed by a letter.
gdb supports multiple command interpreters, and some command infrastructure to allow users or user interface writers to switch between interpreters or run commands in other interpreters.
gdb currently supports two command interpreters, the console interpreter (sometimes called the command-line interpreter or cli) and the machine interface interpreter (or gdb/mi). This manual describes both of these interfaces in great detail.
By default, gdb will start with the console interpreter. However, the user may choose to start gdb with another interpreter by specifying the -i or --interpreter startup options. Defined interpreters include:
consolemimi2). Used primarily
by programs wishing to use gdb as a backend for a debugger GUI
or an IDE. For more information, see The gdb/mi Interface.
mi2mi1The interpreter being used by gdb may not be dynamically switched at runtime. Although possible, this could lead to a very precarious situation. Consider an IDE using gdb/mi. If a user enters the command "interpreter-set console" in a console view, gdb would switch to using the console interpreter, rendering the IDE inoperable!
Although you may only choose a single interpreter at startup, you may execute
commands in any interpreter from the current interpreter using the appropriate
command. If you are running the console interpreter, simply use the
interpreter-exec command:
interpreter-exec mi "-data-list-register-names"
gdb/mi has a similar command, although it is only available in versions of gdb which support gdb/mi version 2 (or greater).
The gdb Text User Interface, TUI in short, is a terminal
interface which uses the curses library to show the source
file, the assembly output, the program registers and gdb
commands in separate text windows.
The TUI is enabled by invoking gdb using either `gdbtui' or `gdb -tui'.
The TUI has two display modes that can be switched while gdb runs:
In the TUI mode, gdb can display several text window on the terminal:
The source and assembly windows show the current program position by highlighting the current line and marking them with the `>' marker. Breakpoints are also indicated with two markers. A first one indicates the breakpoint type:
BbHhThe second marker indicates whether the breakpoint is enabled or not:
+-The source, assembly and register windows are attached to the thread and the frame position. They are updated when the current thread changes, when the frame changes or when the program counter changes. These three windows are arranged by the TUI according to several layouts. The layout defines which of these three windows are visible. The following layouts are available:
On top of the command window a status line gives various information concerning the current process begin debugged. The status line is updated when the information it shows changes. The following fields are displayed:
No process.
?? is displayed.
?? is displayed.
The TUI installs several key bindings in the readline keymaps (see Command Line Editing). They allow to leave or enter in the TUI mode or they operate directly on the TUI layout and windows. The TUI also provides a SingleKey keymap which binds several keys directly to gdb commands. The following key bindings are installed for both TUI mode and the gdb standard mode.
Think of this key binding as the Emacs C-x 1 binding.
Think of it as the Emacs C-x 2 binding.
Think of it as the Emacs C-x o binding.
The following key bindings are handled only by the TUI mode:
In the TUI mode, the arrow keys are used by the active window for scrolling. This means they are available for readline when the active window is the command window. When the command window does not have the focus, it is necessary to use other readline key bindings such as <C-p>, <C-n>, <C-b> and <C-f>.
The TUI provides a SingleKey mode in which it installs a particular key binding in the readline keymaps to connect single keys to some gdb commands.
Other keys temporarily switch to the gdb command prompt. The key that was pressed is inserted in the editing buffer so that it is possible to type most gdb commands without interaction with the TUI SingleKey mode. Once the command is entered the TUI SingleKey mode is restored. The only way to permanently leave this mode is by hitting <q> or `<C-x> <s>'.
The TUI has specific commands to control the text windows. These commands are always available, that is they do not depend on the current terminal mode in which gdb runs. When gdb is in the standard mode, using these commands will automatically switch in the TUI mode.
info winlayout nextlayout prevlayout srclayout asmlayout splitlayout regsfocus next | prev | src | asm | regs | splitrefreshtui reg floattui reg generaltui reg nextgeneral, float, system, vector,
all, save, restore.
tui reg systemupdatewinheight name +countwinheight name -countThe TUI has several configuration variables that control the appearance of windows on the terminal.
set tui border-kind kindspaceasciiacsset tui active-border-mode modenormal, standout, reverse,
half, half-standout, bold and bold-standout.
set tui border-mode modenormalstandoutreversehalfhalf-standoutboldbold-standoutA special interface allows you to use gnu Emacs to view (and edit) the source files for the program you are debugging with gdb.
To use this interface, use the command M-x gdb in Emacs. Give the executable file you want to debug as an argument. This command starts gdb as a subprocess of Emacs, with input and output through a newly created Emacs buffer.
Using gdb under Emacs is just like using gdb normally except for two things:
This applies both to gdb commands and their output, and to the input and output done by the program you are debugging.
This is useful because it means that you can copy the text of previous commands and input them again; you can even use parts of the output in this way.
All the facilities of Emacs' Shell mode are available for interacting with your program. In particular, you can send signals the usual way—for example, C-c C-c for an interrupt, C-c C-z for a stop.
Each time gdb displays a stack frame, Emacs automatically finds the source file for that frame and puts an arrow (`=>') at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the screen to show both your gdb session and the source.
Explicit gdb list or search commands still produce output as
usual, but you probably have no reason to use them from Emacs.
If you specify an absolute file name when prompted for the M-x
gdb argument, then Emacs sets your current working directory to where
your program resides. If you only specify the file name, then Emacs
sets your current working directory to to the directory associated
with the previous buffer. In this case, gdb may find your
program by searching your environment's PATH variable, but on
some operating systems it might not find the source. So, although the
gdb input and output session proceeds normally, the auxiliary
buffer does not display the current source and line of execution.
The initial working directory of gdb is printed on the top line of the gdb I/O buffer and this serves as a default for the commands that specify files for gdb to operate on. See Commands to specify files.
By default, M-x gdb calls the program called gdb. If you
need to call gdb by a different name (for example, if you
keep several configurations around, with different names) you can
customize the Emacs variable gud-gdb-command-name to run the
one you want.
In the gdb I/O buffer, you can use these special Emacs commands in addition to the standard Shell mode commands:
step command; also
update the display window to show the current file and location.
next command. Then update the display window
to show the current file and location.
stepi command; update
display window accordingly.
finish command.
continue
command.
up command.
down command.
In any source file, the Emacs command C-x SPC (gud-break)
tells gdb to set a breakpoint on the source line point is on.
If you type M-x speedbar, then Emacs displays a separate frame which shows a backtrace when the gdb I/O buffer is current. Move point to any frame in the stack and type <RET> to make it become the current frame and display the associated source in the source buffer. Alternatively, click Mouse-2 to make the selected frame become the current one.
If you accidentally delete the source-display buffer, an easy way to get
it back is to type the command f in the gdb buffer, to
request a frame display; when you run under Emacs, this recreates
the source buffer if necessary to show you the context of the current
frame.
The source files displayed in Emacs are in ordinary Emacs buffers which are visiting the source files in the usual way. You can edit the files with these buffers if you wish; but keep in mind that gdb communicates with Emacs in terms of line numbers. If you add or delete lines from the text, the line numbers that gdb knows cease to correspond properly with the code.
The description given here is for GNU Emacs version 21.3 and a more detailed description of its interaction with gdb is given in the Emacs manual (see Debuggers).
gdb/mi is a line based machine oriented text interface to gdb. It is specifically intended to support the development of systems which use the debugger as just one small component of a larger system.
This chapter is a specification of the gdb/mi interface. It is written in the form of a reference manual.
Note that gdb/mi is still under construction, so some of the features described below are incomplete and subject to change.
This chapter uses the following notation:
| separates two alternatives.
[ something ] indicates that something is optional:
it may or may not be given.
( group )* means that group inside the parentheses
may repeat zero or more times.
( group )+ means that group inside the parentheses
may repeat one or more times.
"string" means a literal string.
In alphabetic order: Andrew Cagney, Fernando Nasser, Stan Shebs and Elena Zannoni.
==> | mi-command
==>[ token ] cli-command nl, where
cli-command is any existing gdb CLI command.
==>[ token ] "-" operation ( " " option )*
[ " --" ] ( " " parameter )* nl
==> ==>"-" parameter [ " " parameter ]
==> | c-string
==> ==> ==>""" seven-bit-iso-c-string-content """
==>CR | CR-LF
Notes:
Pragmatics:
The output from gdb/mi consists of zero or more out-of-band records followed, optionally, by a single result record. This result record is for the most recent command. The sequence of output records is terminated by `(gdb)'.
If an input command was prefixed with a token then the corresponding output for that command will also be prefixed by that same token.
==>( out-of-band-record )* [ result-record ] "(gdb)" nl
==> [ token ] "^" result-class ( "," result )* nl
==> | stream-record
==> | status-async-output | notify-async-output
==>[ token ] "*" async-output
==>[ token ] "+" async-output
==>[ token ] "=" async-output
==> ( "," result )* nl
==>"done" | "running" | "connected" | "error" | "exit"
==>"stopped" | others (where others will be added
depending on the needs—this is still in development).
==> "=" value
==> ==> | tuple | list
==> ==> "{}" | "{" result ( "," result )* "}"
==> "[]" | "[" value ( "," value )* "]" | "["
result ( "," result )* "]"
==> | target-stream-output | log-stream-output
==>"~" c-string
==>"@" c-string
==>"&" c-string
==>CR | CR-LF
==>Notes:
See gdb/mi Stream Records, for more details about the various output records.
This subsection presents several simple examples of interaction using the gdb/mi interface. In these examples, `->' means that the following line is passed to gdb/mi as input, while `<-' means the output received from gdb/mi.
Here's an example of stopping the inferior process:
-> -stop
<- (gdb)
and later:
<- *stop,reason="stop",address="0x123",source="a.c:123"
<- (gdb)
Here's an example of a simple CLI command being passed through gdb/mi and on to the CLI.
-> print 1+2
<- &"print 1+2\n"
<- ~"$1 = 3\n"
<- ^done
<- (gdb)
-> -symbol-file xyz.exe
<- *breakpoint,nr="3",address="0x123",source="a.c:123"
<- (gdb)
Here's what happens if you pass a non-existent command:
-> -rubbish
<- ^error,msg="Undefined MI command: rubbish"
<- (gdb)
To help users familiar with gdb's existing CLI interface, gdb/mi accepts existing CLI commands. As specified by the syntax, such commands can be directly entered into the gdb/mi interface and gdb will respond.
This mechanism is provided as an aid to developers of gdb/mi clients and not as a reliable interface into the CLI. Since the command is being interpreteted in an environment that assumes gdb/mi behaviour, the exact output of such commands is likely to end up being an un-supported hybrid of gdb/mi and CLI output.
In addition to a number of out-of-band notifications, the response to a gdb/mi command includes one of the following result indications:
"^done" [ "," results ]"^running""^error" "," c-stringgdb internally maintains a number of output streams: the console, the target, and the log. The output intended for each of these streams is funneled through the gdb/mi interface using stream records.
Each stream record begins with a unique prefix character which identifies its stream (see gdb/mi Output Syntax). In addition to the prefix, each stream record contains a string-output. This is either raw text (with an implicit new line) or a quoted C string (which does not contain an implicit newline).
"~" string-output"@" string-output"&" string-outputOut-of-band records are used to notify the gdb/mi client of additional changes that have occurred. Those changes can either be a consequence of gdb/mi (e.g., a breakpoint modified) or a result of target activity (e.g., target stopped).
The following is a preliminary list of possible out-of-band records.
"*" "stop"The remaining sections describe blocks of commands. Each block of commands is laid out in a fashion similar to this section.
Note the the line breaks shown in the examples are here only for readability. They don't appear in the real output. Also note that the commands with a non-available example (N.A.) are not yet implemented.
The motivation for this collection of commands.
A brief introduction to this collection of commands as a whole.
For each command in the block, the following is described:
-command args...
The corresponding gdb CLI command.
This section documents gdb/mi commands for manipulating breakpoints.
-break-after Command-break-after number count
The breakpoint number number is not in effect until it has been hit count times. To see how this is reflected in the output of the `-break-list' command, see the description of the `-break-list' command below.
The corresponding gdb command is `ignore'.
(gdb)
-break-insert main
^done,bkpt={number="1",addr="0x000100d0",file="hello.c",line="5"}
(gdb)
-break-after 1 3
~
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0",
ignore="3"}]}
(gdb)
-break-condition Command-break-condition number expr
Breakpoint number will stop the program only if the condition in expr is true. The condition becomes part of the `-break-list' output (see the description of the `-break-list' command below).
The corresponding gdb command is `condition'.
(gdb)
-break-condition 1 1
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",cond="1",
times="0",ignore="3"}]}
(gdb)
-break-delete Command-break-delete ( breakpoint )+
Delete the breakpoint(s) whose number(s) are specified in the argument list. This is obviously reflected in the breakpoint list.
The corresponding gdb command is `delete'.
(gdb)
-break-delete 1
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[]}
(gdb)
-break-disable Command-break-disable ( breakpoint )+
Disable the named breakpoint(s). The field `enabled' in the break list is now set to `n' for the named breakpoint(s).
The corresponding gdb command is `disable'.
(gdb)
-break-disable 2
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="n",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0"}]}
(gdb)
-break-enable Command-break-enable ( breakpoint )+
Enable (previously disabled) breakpoint(s).
The corresponding gdb command is `enable'.
(gdb)
-break-enable 2
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0"}]}
(gdb)
-break-info Command-break-info breakpoint
Get information about a single breakpoint.
The corresponding gdb command is `info break breakpoint'.
N.A.
-break-insert Command -break-insert [ -t ] [ -h ] [ -r ]
[ -c condition ] [ -i ignore-count ]
[ -p thread ] [ line | addr ]
If specified, line, can be one of:
The possible optional parameters of this command are:
The result is in the form:
^done,bkptno="number",func="funcname",
file="filename",line="lineno"
where number is the gdb number for this breakpoint, funcname is the name of the function where the breakpoint was inserted, filename is the name of the source file which contains this function, and lineno is the source line number within that file.
Note: this format is open to change.
The corresponding gdb commands are `break', `tbreak', `hbreak', `thbreak', and `rbreak'.
(gdb)
-break-insert main
^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",line="4"}
(gdb)
-break-insert -t foo
^done,bkpt={number="2",addr="0x00010774",file="recursive2.c",line="11"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x0001072c", func="main",file="recursive2.c",line="4",times="0"},
bkpt={number="2",type="breakpoint",disp="del",enabled="y",
addr="0x00010774",func="foo",file="recursive2.c",line="11",times="0"}]}
(gdb)
-break-insert -r foo.*
~int foo(int, int);
^done,bkpt={number="3",addr="0x00010774",file="recursive2.c",line="11"}
(gdb)
-break-list Command-break-list
Displays the list of inserted breakpoints, showing the following fields:
If there are no breakpoints or watchpoints, the BreakpointTable
body field is an empty list.
The corresponding gdb command is `info break'.
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0"},
bkpt={number="2",type="breakpoint",disp="keep",enabled="y",
addr="0x00010114",func="foo",file="hello.c",line="13",times="0"}]}
(gdb)
Here's an example of the result when there are no breakpoints:
(gdb)
-break-list
^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[]}
(gdb)
-break-watch Command-break-watch [ -a | -r ]
Create a watchpoint. With the `-a' option it will create an access watchpoint, i.e. a watchpoint that triggers either on a read from or on a write to the memory location. With the `-r' option, the watchpoint created is a read watchpoint, i.e. it will trigger only when the memory location is accessed for reading. Without either of the options, the watchpoint created is a regular watchpoint, i.e. it will trigger when the memory location is accessed for writing. See Setting watchpoints.
Note that `-break-list' will report a single list of watchpoints and breakpoints inserted.
The corresponding gdb commands are `watch', `awatch', and `rwatch'.
Setting a watchpoint on a variable in the main function:
(gdb)
-break-watch x
^done,wpt={number="2",exp="x"}
(gdb)
-exec-continue
^running
^done,reason="watchpoint-trigger",wpt={number="2",exp="x"},
value={old="-268439212",new="55"},
frame={func="main",args=[],file="recursive2.c",line="5"}
(gdb)
Setting a watchpoint on a variable local to a function. gdb will stop the program execution twice: first for the variable changing value, then for the watchpoint going out of scope.
(gdb)
-break-watch C
^done,wpt={number="5",exp="C"}
(gdb)
-exec-continue
^running
^done,reason="watchpoint-trigger",
wpt={number="5",exp="C"},value={old="-276895068",new="3"},
frame={func="callee4",args=[],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="13"}
(gdb)
-exec-continue
^running
^done,reason="watchpoint-scope",wpnum="5",
frame={func="callee3",args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="18"}
(gdb)
Listing breakpoints and watchpoints, at different points in the program execution. Note that once the watchpoint goes out of scope, it is deleted.
(gdb)
-break-watch C
^done,wpt={number="2",exp="C"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"},
bkpt={number="2",type="watchpoint",disp="keep",
enabled="y",addr="",what="C",times="0"}]}
(gdb)
-exec-continue
^running
^done,reason="watchpoint-trigger",wpt={number="2",exp="C"},
value={old="-276895068",new="3"},
frame={func="callee4",args=[],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="13"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"},
bkpt={number="2",type="watchpoint",disp="keep",
enabled="y",addr="",what="C",times="-5"}]}
(gdb)
-exec-continue
^running
^done,reason="watchpoint-scope",wpnum="2",
frame={func="callee3",args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="18"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"}]}
(gdb)
This section describes the gdb/mi commands that manipulate data: examine memory and registers, evaluate expressions, etc.
-data-disassemble Command -data-disassemble
[ -s start-addr -e end-addr ]
| [ -f filename -l linenum [ -n lines ] ]
-- mode
Where:
$pc)
The output for each instruction is composed of four fields:
Note that whatever included in the instruction field, is not manipulated directely by gdb/mi, i.e. it is not possible to adjust its format.
There's no direct mapping from this command to the CLI.
Disassemble from the current value of $pc to $pc + 20:
(gdb)
-data-disassemble -s $pc -e "$pc + 20" -- 0
^done,
asm_insns=[
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"},
{address="0x000107c8",func-name="main",offset="12",
inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"},
{address="0x000107cc",func-name="main",offset="16",
inst="sethi %hi(0x11800), %o2"},
{address="0x000107d0",func-name="main",offset="20",
inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"}]
(gdb)
Disassemble the whole main function. Line 32 is part of
main.
-data-disassemble -f basics.c -l 32 -- 0
^done,asm_insns=[
{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"},
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"},
[...]
{address="0x0001081c",func-name="main",offset="96",inst="ret "},
{address="0x00010820",func-name="main",offset="100",inst="restore "}]
(gdb)
Disassemble 3 instructions from the start of main:
(gdb)
-data-disassemble -f basics.c -l 32 -n 3 -- 0
^done,asm_insns=[
{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"},
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"}]
(gdb)
Disassemble 3 instructions from the start of main in mixed mode:
(gdb)
-data-disassemble -f basics.c -l 32 -n 3 -- 1
^done,asm_insns=[
src_and_asm_line={line="31",
file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
testsuite/gdb.mi/basics.c",line_asm_insn=[
{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"}]},
src_and_asm_line={line="32",
file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
testsuite/gdb.mi/basics.c",line_asm_insn=[
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"}]}]
(gdb)
-data-evaluate-expression Command-data-evaluate-expression expr
Evaluate expr as an expression. The expression could contain an inferior function call. The function call will execute synchronously. If the expression contains spaces, it must be enclosed in double quotes.
The corresponding gdb commands are `print', `output', and
`call'. In gdbtk only, there's a corresponding
`gdb_eval' command.
In the following example, the numbers that precede the commands are the tokens described in gdb/mi Command Syntax. Notice how gdb/mi returns the same tokens in its output.
211-data-evaluate-expression A
211^done,value="1"
(gdb)
311-data-evaluate-expression &A
311^done,value="0xefffeb7c"
(gdb)
411-data-evaluate-expression A+3
411^done,value="4"
(gdb)
511-data-evaluate-expression "A + 3"
511^done,value="4"
(gdb)
-data-list-changed-registers Command-data-list-changed-registers
Display a list of the registers that have changed.
gdb doesn't have a direct analog for this command; gdbtk
has the corresponding command `gdb_changed_register_list'.
On a PPC MBX board:
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="breakpoint-hit",bkptno="1",frame={func="main",
args=[],file="try.c",line="5"}
(gdb)
-data-list-changed-registers
^done,changed-registers=["0","1","2","4","5","6","7","8","9",
"10","11","13","14","15","16","17","18","19","20","21","22","23",
"24","25","26","27","28","30","31","64","65","66","67","69"]
(gdb)
-data-list-register-names Command-data-list-register-names [ ( regno )+ ]
Show a list of register names for the current target. If no arguments are given, it shows a list of the names of all the registers. If integer numbers are given as arguments, it will print a list of the names of the registers corresponding to the arguments. To ensure consistency between a register name and its number, the output list may include empty register names.
gdb does not have a command which corresponds to
`-data-list-register-names'. In gdbtk there is a
corresponding command `gdb_regnames'.
For the PPC MBX board:
(gdb)
-data-list-register-names
^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
"r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
"r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
"r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
"f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
"f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
"", "pc","ps","cr","lr","ctr","xer"]
(gdb)
-data-list-register-names 1 2 3
^done,register-names=["r1","r2","r3"]
(gdb)
-data-list-register-values Command-data-list-register-values fmt [ ( regno )*]
Display the registers' contents. fmt is the format according to which the registers' contents are to be returned, followed by an optional list of numbers specifying the registers to display. A missing list of numbers indicates that the contents of all the registers must be returned.
Allowed formats for fmt are:
xotdrNThe corresponding gdb commands are `info reg', `info
all-reg', and (in gdbtk) `gdb_fetch_registers'.
For a PPC MBX board (note: line breaks are for readability only, they don't appear in the actual output):
(gdb)
-data-list-register-values r 64 65
^done,register-values=[{number="64",value="0xfe00a300"},
{number="65",value="0x00029002"}]
(gdb)
-data-list-register-values x
^done,register-values=[{number="0",value="0xfe0043c8"},
{number="1",value="0x3fff88"},{number="2",value="0xfffffffe"},
{number="3",value="0x0"},{number="4",value="0xa"},
{number="5",value="0x3fff68"},{number="6",value="0x3fff58"},
{number="7",value="0xfe011e98"},{number="8",value="0x2"},
{number="9",value="0xfa202820"},{number="10",value="0xfa202808"},
{number="11",value="0x1"},{number="12",value="0x0"},
{number="13",value="0x4544"},{number="14",value="0xffdfffff"},
{number="15",value="0xffffffff"},{number="16",value="0xfffffeff"},
{number="17",value="0xefffffed"},{number="18",value="0xfffffffe"},
{number="19",value="0xffffffff"},{number="20",value="0xffffffff"},
{number="21",value="0xffffffff"},{number="22",value="0xfffffff7"},
{number="23",value="0xffffffff"},{number="24",value="0xffffffff"},
{number="25",value="0xffffffff"},{number="26",value="0xfffffffb"},
{number="27",value="0xffffffff"},{number="28",value="0xf7bfffff"},
{number="29",value="0x0"},{number="30",value="0xfe010000"},
{number="31",value="0x0"},{number="32",value="0x0"},
{number="33",value="0x0"},{number="34",value="0x0"},
{number="35",value="0x0"},{number="36",value="0x0"},
{number="37",value="0x0"},{number="38",value="0x0"},
{number="39",value="0x0"},{number="40",value="0x0"},
{number="41",value="0x0"},{number="42",value="0x0"},
{number="43",value="0x0"},{number="44",value="0x0"},
{number="45",value="0x0"},{number="46",value="0x0"},
{number="47",value="0x0"},{number="48",value="0x0"},
{number="49",value="0x0"},{number="50",value="0x0"},
{number="51",value="0x0"},{number="52",value="0x0"},
{number="53",value="0x0"},{number="54",value="0x0"},
{number="55",value="0x0"},{number="56",value="0x0"},
{number="57",value="0x0"},{number="58",value="0x0"},
{number="59",value="0x0"},{number="60",value="0x0"},
{number="61",value="0x0"},{number="62",value="0x0"},
{number="63",value="0x0"},{number="64",value="0xfe00a300"},
{number="65",value="0x29002"},{number="66",value="0x202f04b5"},
{number="67",value="0xfe0043b0"},{number="68",value="0xfe00b3e4"},
{number="69",value="0x20002b03"}]
(gdb)
-data-read-memory Command -data-read-memory [ -o byte-offset ]
address word-format word-size
nr-rows nr-cols [ aschar ]
where:
print command (see Output formats).
This command displays memory contents as a table of nr-rows by
nr-cols words, each word being word-size bytes. In total,
nr-rows * nr-cols * word-size bytes are read
(returned as `total-bytes'). Should less than the requested number
of bytes be returned by the target, the missing words are identified
using `N/A'. The number of bytes read from the target is returned
in `nr-bytes' and the starting address used to read memory in
`addr'.
The address of the next/previous row or page is available in `next-row' and `prev-row', `next-page' and `prev-page'.
The corresponding gdb command is `x'. gdbtk has
`gdb_get_mem' memory read command.
Read six bytes of memory starting at bytes+6 but then offset by
-6 bytes. Format as three rows of two columns. One byte per
word. Display each word in hex.
(gdb)
9-data-read-memory -o -6 -- bytes+6 x 1 3 2
9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
prev-page="0x0000138a",memory=[
{addr="0x00001390",data=["0x00","0x01"]},
{addr="0x00001392",data=["0x02","0x03"]},
{addr="0x00001394",data=["0x04","0x05"]}]
(gdb)
Read two bytes of memory starting at address shorts + 64 and
display as a single word formatted in decimal.
(gdb)
5-data-read-memory shorts+64 d 2 1 1
5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
next-row="0x00001512",prev-row="0x0000150e",
next-page="0x00001512",prev-page="0x0000150e",memory=[
{addr="0x00001510",data=["128"]}]
(gdb)
Read thirty two bytes of memory starting at bytes+16 and format
as eight rows of four columns. Include a string encoding with `x'
used as the non-printable character.
(gdb)
4-data-read-memory bytes+16 x 1 8 4 x
4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
next-row="0x000013c0",prev-row="0x0000139c",
next-page="0x000013c0",prev-page="0x00001380",memory=[
{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"},
{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"},
{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"},
{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"},
{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"},
{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"},
{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"},
{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"}]
(gdb)
-display-delete Command-display-delete number
Delete the display number.
The corresponding gdb command is `delete display'.
N.A.
-display-disable Command-display-disable number
Disable display number.
The corresponding gdb command is `disable display'.
N.A.
-display-enable Command-display-enable number
Enable display number.
The corresponding gdb command is `enable display'.
N.A.
-display-insert Command-display-insert expression
Display expression every time the program stops.
The corresponding gdb command is `display'.
N.A.
-display-list Command-display-list
List the displays. Do not show the current values.
The corresponding gdb command is `info display'.
N.A.
-environment-cd Command-environment-cd pathdir
Set gdb's working directory.
The corresponding gdb command is `cd'.
(gdb)
-environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
^done
(gdb)
-environment-directory Command-environment-directory [ -r ] [ pathdir ]+
Add directories pathdir to beginning of search path for source files. If the `-r' option is used, the search path is reset to the default search path. If directories pathdir are supplied in addition to the `-r' option, the search path is first reset and then addition occurs as normal. Multiple directories may be specified, separated by blanks. Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command. If blanks are needed as part of a directory name, double-quotes should be used around the name. In the command output, the path will show up separated by the system directory-separator character. The directory-seperator character must not be used in any directory name. If no directories are specified, the current search path is displayed.
The corresponding gdb command is `dir'.
(gdb)
-environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
(gdb)
-environment-directory ""
^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
(gdb)
-environment-directory -r /home/jjohnstn/src/gdb /usr/src
^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
(gdb)
-environment-directory -r
^done,source-path="$cdir:$cwd"
(gdb)
-environment-path Command-environment-path [ -r ] [ pathdir ]+
Add directories pathdir to beginning of search path for object files. If the `-r' option is used, the search path is reset to the original search path that existed at gdb start-up. If directories pathdir are supplied in addition to the `-r' option, the search path is first reset and then addition occurs as normal. Multiple directories may be specified, separated by blanks. Specifying multiple directories in a single command results in the directories added to the beginning of the search path in the same order they were presented in the command. If blanks are needed as part of a directory name, double-quotes should be used around the name. In the command output, the path will show up separated by the system directory-separator character. The directory-seperator character must not be used in any directory name. If no directories are specified, the current path is displayed.
The corresponding gdb command is `path'.
(gdb)
-environment-path
^done,path="/usr/bin"
(gdb)
-environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
(gdb)
-environment-path -r /usr/local/bin
^done,path="/usr/local/bin:/usr/bin"
(gdb)
-environment-pwd Command-environment-pwd
Show the current working directory.
The corresponding gdb command is `pwd'.
(gdb)
-environment-pwd
^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
(gdb)
As a result of execution, the inferior program can run to completion, if it doesn't encounter any breakpoints. In this case the output will include an exit code, if the program has exited exceptionally.
Program exited normally:
(gdb)
-exec-run
^running
(gdb)
x = 55
*stopped,reason="exited-normally"
(gdb)
Program exited exceptionally:
(gdb)
-exec-run
^running
(gdb)
x = 55
*stopped,reason="exited",exit-code="01"
(gdb)
Another way the program can terminate is if it receives a signal such as
SIGINT. In this case, gdb/mi displays this:
(gdb)
*stopped,reason="exited-signalled",signal-name="SIGINT",
signal-meaning="Interrupt"
-exec-abort Command-exec-abort
Kill the inferior running program.
The corresponding gdb command is `kill'.
N.A.
-exec-arguments Command-exec-arguments args
Set the inferior program arguments, to be used in the next `-exec-run'.
The corresponding gdb command is `set args'.
Don't have one around.
-exec-continue Command-exec-continue
Asynchronous command. Resumes the execution of the inferior program until a breakpoint is encountered, or until the inferior exits.
The corresponding gdb corresponding is `continue'.
-exec-continue
^running
(gdb)
@Hello world
*stopped,reason="breakpoint-hit",bkptno="2",frame={func="foo",args=[],
file="hello.c",line="13"}
(gdb)
-exec-finish Command-exec-finish
Asynchronous command. Resumes the execution of the inferior program until the current function is exited. Displays the results returned by the function.
The corresponding gdb command is `finish'.
Function returning void.
-exec-finish
^running
(gdb)
@hello from foo
*stopped,reason="function-finished",frame={func="main",args=[],
file="hello.c",line="7"}
(gdb)
Function returning other than void. The name of the internal
gdb variable storing the result is printed, together with the
value itself.
-exec-finish
^running
(gdb)
*stopped,reason="function-finished",frame={addr="0x000107b0",func="foo",
args=[{name="a",value="1"],{name="b",value="9"}},
file="recursive2.c",line="14"},
gdb-result-var="$1",return-value="0"
(gdb)
-exec-interrupt Command-exec-interrupt
Asynchronous command. Interrupts the background execution of the target. Note how the token associated with the stop message is the one for the execution command that has been interrupted. The token for the interrupt itself only appears in the `^done' output. If the user is trying to interrupt a non-running program, an error message will be printed.
The corresponding gdb command is `interrupt'.
(gdb)
111-exec-continue
111^running
(gdb)
222-exec-interrupt
222^done
(gdb)
111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
frame={addr="0x00010140",func="foo",args=[],file="try.c",line="13"}
(gdb)
(gdb)
-exec-interrupt
^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
(gdb)
-exec-next Command-exec-next
Asynchronous command. Resumes execution of the inferior program, stopping when the beginning of the next source line is reached.
The corresponding gdb command is `next'.
-exec-next
^running
(gdb)
*stopped,reason="end-stepping-range",line="8",file="hello.c"
(gdb)
-exec-next-instruction Command-exec-next-instruction
Asynchronous command. Executes one machine instruction. If the instruction is a function call continues until the function returns. If the program stops at an instruction in the middle of a source line, the address will be printed as well.
The corresponding gdb command is `nexti'.
(gdb)
-exec-next-instruction
^running
(gdb)
*stopped,reason="end-stepping-range",
addr="0x000100d4",line="5",file="hello.c"
(gdb)
-exec-return Command-exec-return
Makes current function return immediately. Doesn't execute the inferior. Displays the new current frame.
The corresponding gdb command is `return'.
(gdb)
200-break-insert callee4
200^done,bkpt={number="1",addr="0x00010734",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"}
(gdb)
000-exec-run
000^running
(gdb)
000*stopped,reason="breakpoint-hit",bkptno="1",
frame={func="callee4",args=[],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"}
(gdb)
205-break-delete
205^done
(gdb)
111-exec-return
111^done,frame={level="0",func="callee3",
args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="18"}
(gdb)
-exec-run Command-exec-run
Asynchronous command. Starts execution of the inferior from the beginning. The inferior executes until either a breakpoint is encountered or the program exits.
The corresponding gdb command is `run'.
(gdb)
-break-insert main
^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",line="4"}
(gdb)
-exec-run
^running
(gdb)
*stopped,reason="breakpoint-hit",bkptno="1",
frame={func="main",args=[],file="recursive2.c",line="4"}
(gdb)
-exec-show-arguments Command-exec-show-arguments
Print the arguments of the program.
The corresponding gdb command is `show args'.
N.A.
-exec-step Command-exec-step
Asynchronous command. Resumes execution of the inferior program, stopping when the beginning of the next source line is reached, if the next source line is not a function call. If it is, stop at the first instruction of the called function.
The corresponding gdb command is `step'.
Stepping into a function:
-exec-step
^running
(gdb)
*stopped,reason="end-stepping-range",
frame={func="foo",args=[{name="a",value="10"},
{name="b",value="0"}],file="recursive2.c",line="11"}
(gdb)
Regular stepping:
-exec-step
^running
(gdb)
*stopped,reason="end-stepping-range",line="14",file="recursive2.c"
(gdb)
-exec-step-instruction Command-exec-step-instruction
Asynchronous command. Resumes the inferior which executes one machine instruction. The output, once gdb has stopped, will vary depending on whether we have stopped in the middle of a source line or not. In the former case, the address at which the program stopped will be printed as well.
The corresponding gdb command is `stepi'.
(gdb)
-exec-step-instruction
^running
(gdb)
*stopped,reason="end-stepping-range",
frame={func="foo",args=[],file="try.c",line="10"}
(gdb)
-exec-step-instruction
^running
(gdb)
*stopped,reason="end-stepping-range",
frame={addr="0x000100f4",func="foo",args=[],file="try.c",line="10"}
(gdb)
-exec-until Command-exec-until [ location ]
Asynchronous command. Executes the inferior until the location specified in the argument is reached. If there is no argument, the inferior executes until a source line greater than the current one is reached. The reason for stopping in this case will be `location-reached'.
The corresponding gdb command is `until'.
(gdb)
-exec-until recursive2.c:6
^running
(gdb)
x = 55
*stopped,reason="location-reached",frame={func="main",args=[],
file="recursive2.c",line="6"}
(gdb)
-file-exec-and-symbols Command-file-exec-and-symbols file
Specify the executable file to be debugged. This file is the one from which the symbol table is also read. If no file is specified, the command clears the executable and symbol information. If breakpoints are set when using this command with no arguments, gdb will produce error messages. Otherwise, no output is produced, except a completion notification.
The corresponding gdb command is `file'.
(gdb)
-file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)
-file-exec-file Command-file-exec-file file
Specify the executable file to be debugged. Unlike `-file-exec-and-symbols', the symbol table is not read from this file. If used without argument, gdb clears the information about the executable file. No output is produced, except a completion notification.
The corresponding gdb command is `exec-file'.
(gdb)
-file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)
-file-list-exec-sections Command-file-list-exec-sections
List the sections of the current executable file.
The gdb command `info file' shows, among the rest, the same
information as this command. gdbtk has a corresponding command
`gdb_load_info'.
N.A.
-file-list-exec-source-file Command-file-list-exec-source-file
List the line number, the current source file, and the absolute path to the current source file for the current executable.
There's no gdb command which directly corresponds to this one.
(gdb)
123-file-list-exec-source-file
123^done,line="1",file="foo.c",fullname="/home/bar/foo.c"
(gdb)
-file-list-exec-source-files Command-file-list-exec-source-files
List the source files for the current executable.
There's no gdb command which directly corresponds to this one.
gdbtk has an analogous command `gdb_listfiles'.
N.A.
-file-list-shared-libraries Command-file-list-shared-libraries
List the shared libraries in the program.
The corresponding gdb command is `info shared'.
N.A.
-file-list-symbol-files Command-file-list-symbol-files
List symbol files.
The corresponding gdb command is `info file' (part of it).
N.A.
-file-symbol-file Command-file-symbol-file file
Read symbol table info from the specified file argument. When used without arguments, clears gdb's symbol table info. No output is produced, except for a completion notification.
The corresponding gdb command is `symbol-file'.
(gdb)
-file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)
-gdb-exit Command-gdb-exit
Exit gdb immediately.
Approximately corresponds to `quit'.
(gdb)
-gdb-exit
-gdb-set Command-gdb-set
Set an internal gdb variable.
The corresponding gdb command is `set'.
(gdb)
-gdb-set $foo=3
^done
(gdb)
-gdb-show Command-gdb-show
Show the current value of a gdb variable.
The corresponding gdb command is `show'.
(gdb)
-gdb-show annotate
^done,value="0"
(gdb)
-gdb-version Command-gdb-version
Show version information for gdb. Used mostly in testing.
There's no equivalent gdb command. gdb by default shows this information when you start an interactive session.
(gdb)
-gdb-version
~GNU gdb 5.2.1
~Copyright 2000 Free Software Foundation, Inc.
~GDB is free software, covered by the GNU General Public License, and
~you are welcome to change it and/or distribute copies of it under
~ certain conditions.
~Type "show copying" to see the conditions.
~There is absolutely no warranty for GDB. Type "show warranty" for
~ details.
~This GDB was configured as
"--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
^done
(gdb)
-interpreter-exec Command-interpreter-exec interpreter command
Execute the specified command in the given interpreter.
The corresponding gdb command is `interpreter-exec'.
(gdb)
-interpreter-exec console "break main"
&"During symbol reading, couldn't parse type; debugger out of date?.\n"
&"During symbol reading, bad structure-type format.\n"
~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
^done
(gdb)
-stack-info-frame Command-stack-info-frame
Get info on the current frame.
The corresponding gdb command is `info frame' or `frame' (without arguments).
N.A.
-stack-info-depth Command-stack-info-depth [ max-depth ]
Return the depth of the stack. If the integer argument max-depth is specified, do not count beyond max-depth frames.
There's no equivalent gdb command.
For a stack with frame levels 0 through 11:
(gdb)
-stack-info-depth
^done,depth="12"
(gdb)
-stack-info-depth 4
^done,depth="4"
(gdb)
-stack-info-depth 12
^done,depth="12"
(gdb)
-stack-info-depth 11
^done,depth="11"
(gdb)
-stack-info-depth 13
^done,depth="12"
(gdb)
-stack-list-arguments Command -stack-list-arguments show-values
[ low-frame high-frame ]
Display a list of the arguments for the frames between low-frame and high-frame (inclusive). If low-frame and high-frame are not provided, list the arguments for the whole call stack.
The show-values argument must have a value of 0 or 1. A value of 0 means that only the names of the arguments are listed, a value of 1 means that both names and values of the arguments are printed.
gdb does not have an equivalent command. gdbtk has a
`gdb_get_args' command which partially overlaps with the
functionality of `-stack-list-arguments'.
(gdb)
-stack-list-frames
^done,
stack=[
frame={level="0",addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"},
frame={level="1",addr="0x0001076c",func="callee3",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="17"},
frame={level="2",addr="0x0001078c",func="callee2",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="22"},
frame={level="3",addr="0x000107b4",func="callee1",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="27"},
frame={level="4",addr="0x000107e0",func="main",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="32"}]
(gdb)
-stack-list-arguments 0
^done,
stack-args=[
frame={level="0",args=[]},
frame={level="1",args=[name="strarg"]},
frame={level="2",args=[name="intarg",name="strarg"]},
frame={level="3",args=[name="intarg",name="strarg",name="fltarg"]},
frame={level="4",args=[]}]
(gdb)
-stack-list-arguments 1
^done,
stack-args=[
frame={level="0",args=[]},
frame={level="1",
args=[{name="strarg",value="0x11940 \"A string argument.\""}]},
frame={level="2",args=[
{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""}]},
{frame={level="3",args=[
{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""},
{name="fltarg",value="3.5"}]},
frame={level="4",args=[]}]
(gdb)
-stack-list-arguments 0 2 2
^done,stack-args=[frame={level="2",args=[name="intarg",name="strarg"]}]
(gdb)
-stack-list-arguments 1 2 2
^done,stack-args=[frame={level="2",
args=[{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""}]}]
(gdb)
-stack-list-frames Command-stack-list-frames [ low-frame high-frame ]
List the frames currently on the stack. For each frame it displays the following info:
$pc value for that frame.
$pc.
If invoked without arguments, this command prints a backtrace for the whole stack. If given two integer arguments, it shows the frames whose levels are between the two arguments (inclusive). If the two arguments are equal, it shows the single frame at the corresponding level.
The corresponding gdb commands are `backtrace' and `where'.
Full stack backtrace:
(gdb)
-stack-list-frames
^done,stack=
[frame={level="0",addr="0x0001076c",func="foo",
file="recursive2.c",line="11"},
frame={level="1",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="2",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="4",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="5",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="6",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="7",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="8",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="9",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="10",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="11",addr="0x00010738",func="main",
file="recursive2.c",line="4"}]
(gdb)
Show frames between low_frame and high_frame:
(gdb)
-stack-list-frames 3 5
^done,stack=
[frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="4",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="5",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"}]
(gdb)
Show a single frame:
(gdb)
-stack-list-frames 3 3
^done,stack=
[frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"}]
(gdb)
-stack-list-locals Command-stack-list-locals print-values
Display the local variable names for the current frame. With an
argument of 0 or --no-values, prints only the names of the variables.
With argument of 1 or --all-values, prints also their values. With
argument of 2 or --simple-values, prints the name, type and value for
simple data types and the name and type for arrays, structures and
unions. In this last case, the idea is that the user can see the
value of simple data types immediately and he can create variable
objects for other data types if he wishes to explore their values in
more detail.
`info locals' in gdb, `gdb_get_locals' in gdbtk.
(gdb)
-stack-list-locals 0
^done,locals=[name="A",name="B",name="C"]
(gdb)
-stack-list-locals --all-values
^done,locals=[{name="A",value="1"},{name="B",value="2"},
{name="C",value="{1, 2, 3}"}]
-stack-list-locals --simple-values
^done,locals=[{name="A",type="int",value="1"},
{name="B",type="int",value="2"},{name="C",type="int [3]"}]
(gdb)
-stack-select-frame Command-stack-select-frame framenum
Change the current frame. Select a different frame framenum on the stack.
The corresponding gdb commands are `frame', `up', `down', `select-frame', `up-silent', and `down-silent'.
(gdb)
-stack-select-frame 2
^done
(gdb)
-symbol-info-address Command-symbol-info-address symbol
Describe where symbol is stored.
The corresponding gdb command is `info address'.
N.A.
-symbol-info-file Command-symbol-info-file
Show the file for the symbol.
There's no equivalent gdb command. gdbtk has
`gdb_find_file'.
N.A.
-symbol-info-function Command-symbol-info-function
Show which function the symbol lives in.
`gdb_get_function' in gdbtk.
N.A.
-symbol-info-line Command-symbol-info-line
Show the core addresses of the code for a source line.
The corresponding gdb command is `info line'.
gdbtk has the `gdb_get_line' and `gdb_get_file' commands.
N.A.
-symbol-info-symbol Command-symbol-info-symbol addr
Describe what symbol is at location addr.
The corresponding gdb command is `info symbol'.
N.A.
-symbol-list-functions Command-symbol-list-functions
List the functions in the executable.
`info functions' in gdb, `gdb_listfunc' and
`gdb_search' in gdbtk.
N.A.
-symbol-list-lines Command-symbol-list-lines filename
Print the list of lines that contain code and their associated program addresses for the given source filename. The entries are sorted in ascending PC order.
There is no corresponding gdb command.
(gdb)
-symbol-list-lines basics.c
^done,lines=[{pc="0x08048554",line="7"},{pc="0x0804855a",line="8"}]
(gdb)
-symbol-list-types Command-symbol-list-types
List all the type names.
The corresponding commands are `info types' in gdb,
`gdb_search' in gdbtk.
N.A.
-symbol-list-variables Command-symbol-list-variables
List all the global and static variable names.
`info variables' in gdb, `gdb_search' in gdbtk.
N.A.
-symbol-locate Command-symbol-locate
`gdb_loc' in gdbtk.
N.A.
-symbol-type Command-symbol-type variable
Show type of variable.
The corresponding gdb command is `ptype', gdbtk has
`gdb_obj_variable'.
N.A.
-target-attach Command-target-attach pid | file
Attach to a process pid or a file file outside of gdb.
The corresponding gdb command is `attach'.
N.A.
-target-compare-sections Command-target-compare-sections [ section ]
Compare data of section section on target to the exec file. Without the argument, all sections are compared.
The gdb equivalent is `compare-sections'.
N.A.
-target-detach Command-target-detach
Disconnect from the remote target. There's no output.
The corresponding gdb command is `detach'.
(gdb)
-target-detach
^done
(gdb)
-target-disconnect Command-target-disconnect
Disconnect from the remote target. There's no output.
The corresponding gdb command is `disconnect'.
(gdb)
-target-disconnect
^done
(gdb)
-target-download Command-target-download
Loads the executable onto the remote target. It prints out an update message every half second, which includes the fields:
Each message is sent as status record (see gdb/mi Output Syntax).
In addition, it prints the name and size of the sections, as they are downloaded. These messages include the following fields:
At the end, a summary is printed.
The corresponding gdb command is `load'.
Note: each status message appears on a single line. Here the messages have been broken down so that they can fit onto a page.
(gdb)
-target-download
+download,{section=".text",section-size="6668",total-size="9880"}
+download,{section=".text",section-sent="512",section-size="6668",
total-sent="512",total-size="9880"}
+download,{section=".text",section-sent="1024",section-size="6668",
total-sent="1024",total-size="9880"}
+download,{section=".text",section-sent="1536",section-size="6668",
total-sent="1536",total-size="9880"}
+download,{section=".text",section-sent="2048",section-size="6668",
total-sent="2048",total-size="9880"}
+download,{section=".text",section-sent="2560",section-size="6668",
total-sent="2560",total-size="9880"}
+download,{section=".text",section-sent="3072",section-size="6668",
total-sent="3072",total-size="9880"}
+download,{section=".text",section-sent="3584",section-size="6668",
total-sent="3584",total-size="9880"}
+download,{section=".text",section-sent="4096",section-size="6668",
total-sent="4096",total-size="9880"}
+download,{section=".text",section-sent="4608",section-size="6668",
total-sent="4608",total-size="9880"}
+download,{section=".text",section-sent="5120",section-size="6668",
total-sent="5120",total-size="9880"}
+download,{section=".text",section-sent="5632",section-size="6668",
total-sent="5632",total-size="9880"}
+download,{section=".text",section-sent="6144",section-size="6668",
total-sent="6144",total-size="9880"}
+download,{section=".text",section-sent="6656",section-size="6668",
total-sent="6656",total-size="9880"}
+download,{section=".init",section-size="28",total-size="9880"}
+download,{section=".fini",section-size="28",total-size="9880"}
+download,{section=".data",section-size="3156",total-size="9880"}
+download,{section=".data",section-sent="512",section-size="3156",
total-sent="7236",total-size="9880"}
+download,{section=".data",section-sent="1024",section-size="3156",
total-sent="7748",total-size="9880"}
+download,{section=".data",section-sent="1536",section-size="3156",
total-sent="8260",total-size="9880"}
+download,{section=".data",section-sent="2048",section-size="3156",
total-sent="8772",total-size="9880"}
+download,{section=".data",section-sent="2560",section-size="3156",
total-sent="9284",total-size="9880"}
+download,{section=".data",section-sent="3072",section-size="3156",
total-sent="9796",total-size="9880"}
^done,address="0x10004",load-size="9880",transfer-rate="6586",
write-rate="429"
(gdb)
-target-exec-status Command-target-exec-status
Provide information on the state of the target (whether it is running or not, for instance).
There's no equivalent gdb command.
N.A.
-target-list-available-targets Command-target-list-available-targets
List the possible targets to connect to.
The corresponding gdb command is `help target'.
N.A.
-target-list-current-targets Command-target-list-current-targets
Describe the current target.
The corresponding information is printed by `info file' (among other things).
N.A.
-target-list-parameters Command-target-list-parameters
No equivalent.
N.A.
-target-select Command-target-select type parameters ...
Connect gdb to the remote target. This command takes two args:
The output is a connection notification, followed by the address at which the target program is, in the following form:
^connected,addr="address",func="function name",
args=[arg list]
The corresponding gdb command is `target'.
(gdb)
-target-select async /dev/ttya
^connected,addr="0xfe00a300",func="??",args=[]
(gdb)
-thread-info Command-thread-info
No equivalent.
N.A.
-thread-list-all-threads Command-thread-list-all-threads
The equivalent gdb command is `info threads'.
N.A.
-thread-list-ids Command-thread-list-ids
Produces a list of the currently known gdb thread ids. At the end of the list it also prints the total number of such threads.
Part of `info threads' supplies the same information.
No threads present, besides the main process:
(gdb)
-thread-list-ids
^done,thread-ids={},number-of-threads="0"
(gdb)
Several threads:
(gdb)
-thread-list-ids
^done,thread-ids={thread-id="3",thread-id="2",thread-id="1"},
number-of-threads="3"
(gdb)
-thread-select Command-thread-select threadnum
Make threadnum the current thread. It prints the number of the new current thread, and the topmost frame for that thread.
The corresponding gdb command is `thread'.
(gdb)
-exec-next
^running
(gdb)
*stopped,reason="end-stepping-range",thread-id="2",line="187",
file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
(gdb)
-thread-list-ids
^done,
thread-ids={thread-id="3",thread-id="2",thread-id="1"},
number-of-threads="3"
(gdb)
-thread-select 3
^done,new-thread-id="3",
frame={level="0",func="vprintf",
args=[{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""},
{name="arg",value="0x2"}],file="vprintf.c",line="31"}
(gdb)
The tracepoint commands are not yet implemented.
For the implementation of a variable debugger window (locals, watched
expressions, etc.), we are proposing the adaptation of the existing code
used by Insight.
The two main reasons for that are:
The original interface was designed to be used by Tcl code, so it was slightly changed so it could be used through gdb/mi. This section describes the gdb/mi operations that will be available and gives some hints about their use.
Note: In addition to the set of operations described here, we expect the gui implementation of a variable window to require, at least, the following operations:
-gdb-show output-radix
-stack-list-arguments
-stack-list-locals
-stack-select-frame
The basic idea behind variable objects is the creation of a named object to represent a variable, an expression, a memory location or even a CPU register. For each object created, a set of operations is available for examining or changing its properties.
Furthermore, complex data types, such as C structures, are represented
in a tree format. For instance, the struct type variable is the
root and the children will represent the struct members. If a child
is itself of a complex type, it will also have children of its own.
Appropriate language differences are handled for C, C++ and Java.
When returning the actual values of the objects, this facility allows
for the individual selection of the display format used in the result
creation. It can be chosen among: binary, decimal, hexadecimal, octal
and natural. Natural refers to a default format automatically
chosen based on the variable type (like decimal for an int, hex
for pointers, etc.).
The following is the complete set of gdb/mi operations defined to access this functionality:
| Operation | Description
|
-var-create
| create a variable object
|
-var-delete
| delete the variable object and its children
|
-var-set-format
| set the display format of this variable
|
-var-show-format
| show the display format of this variable
|
-var-info-num-children
| tells how many children this object has
|
-var-list-children
| return a list of the object's children
|
-var-info-type
| show the type of this variable object
|
-var-info-expression
| print what this variable object represents
|
-var-show-attributes
| is this variable editable? does it exist here?
|
-var-evaluate-expression
| get the value of this variable
|
-var-assign
| set the value of this variable
|
-var-update
| update the variable and its children
|
In the next subsection we describe each operation in detail and suggest how it can be used.
-var-create Command -var-create {name | "-"}
{frame-addr | "*"} expression
This operation creates a variable object, which allows the monitoring of a variable, the result of an expression, a memory cell or a CPU register.
The name parameter is the string by which the object can be referenced. It must be unique. If `-' is specified, the varobj system will generate a string “varNNNNNN” automatically. It will be unique provided that one does not specify name on that format. The command fails if a duplicate name is found.
The frame under which the expression should be evaluated can be specified by frame-addr. A `*' indicates that the current frame should be used.
expression is any expression valid on the current language set (must not begin with a `*'), or one of the following:
This operation returns the name, number of children and the type of the object created. Type is returned as a string as the ones generated by the gdb CLI:
name="name",numchild="N",type="type"
-var-delete Command-var-delete name
Deletes a previously created variable object and all of its children.
Returns an error if the object name is not found.
-var-set-format Command-var-set-format name format-spec
Sets the output format for the value of the object name to be format-spec.
The syntax for the format-spec is as follows:
format-spec ==>
{binary | decimal | hexadecimal | octal | natural}
-var-show-format Command-var-show-format name
Returns the format used to display the value of the object name.
format ==>
format-spec
-var-info-num-children Command-var-info-num-children name
Returns the number of children of a variable object name:
numchild=n
-var-list-children Command-var-list-children [print-values] name
Returns a list of the children of the specified variable object. With
just the variable object name as an argument or with an optional
preceding argument of 0 or --no-values, prints only the names of the
variables. With an optional preceding argument of 1 or --all-values,
also prints their values.
(gdb)
-var-list-children n
numchild=n,children=[{name=name,
numchild=n,type=type},(repeats N times)]
(gdb)
-var-list-children --all-values n
numchild=n,children=[{name=name,
numchild=n,value=value,type=type},(repeats N times)]
-var-info-type Command-var-info-type name
Returns the type of the specified variable name. The type is returned as a string in the same format as it is output by the gdb CLI:
type=typename
-var-info-expression Command-var-info-expression name
Returns what is represented by the variable object name:
lang=lang-spec,exp=expression
where lang-spec is {"C" | "C++" | "Java"}.
-var-show-attributes Command-var-show-attributes name
List attributes of the specified variable object name:
status=attr [ ( ,attr )* ]
where attr is { { editable | noneditable } | TBD }.
-var-evaluate-expression Command-var-evaluate-expression name
Evaluates the expression that is represented by the specified variable object and returns its value as a string in the current format specified for the object:
value=value
Note that one must invoke -var-list-children for a variable
before the value of a child variable can be evaluated.
-var-assign Command-var-assign name expression
Assigns the value of expression to the variable object specified
by name. The object must be `editable'. If the variable's
value is altered by the assign, the variable will show up in any
subsequent -var-update list.
(gdb)
-var-assign var1 3
^done,value="3"
(gdb)
-var-update *
^done,changelist=[{name="var1",in_scope="true",type_changed="false"}]
(gdb)
-var-update Command -var-update {name | "*"}
Update the value of the variable object name by evaluating its expression after fetching all the new values from memory or registers. A `*' causes all existing variable objects to be updated.
This chapter describes annotations in gdb. Annotations were designed to interface gdb to graphical user interfaces or other similar programs which want to interact with gdb at a relatively high level.
The annotation mechanism has largely been superseeded by gdb/mi (see GDB/MI).
Annotations start with a newline character, two `control-z' characters, and the name of the annotation. If there is no additional information associated with this annotation, the name of the annotation is followed immediately by a newline. If there is additional information, the name of the annotation is followed by a space, the additional information, and a newline. The additional information cannot contain newline characters.
Any output not beginning with a newline and two `control-z' characters denotes literal output from gdb. Currently there is no need for gdb to output a newline followed by two `control-z' characters, but if there was such a need, the annotations could be extended with an `escape' annotation which means those three characters as output.
The annotation level, which is specified using the --annotate command line option (see Mode Options), controls how much information gdb prints together with its prompt, values of expressions, source lines, and other types of output. Level 0 is for no anntations, level 1 is for use when gdb is run as a subprocess of gnu Emacs, level 3 is the maximum annotation suitable for programs that control gdb, and level 2 annotations have been made obsolete (see Limitations of the Annotation Interface). This chapter describes level 3 annotations.
A simple example of starting up gdb with annotations is:
$ gdb --annotate=3
GNU gdb 6.0
Copyright 2003 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it
under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty"
for details.
This GDB was configured as "i386-pc-linux-gnu"
^Z^Zpre-prompt
(gdb)
^Z^Zprompt
quit
^Z^Zpost-prompt
$
Here `quit' is input to gdb; the rest is output from gdb. The three lines beginning `^Z^Z' (where `^Z' denotes a `control-z' character) are annotations; the rest is output from gdb.
To issue a command to gdb without affecting certain aspects of the state which is seen by users, prefix it with `server '. This means that this command will not affect the command history, nor will it affect gdb's notion of which command to repeat if <RET> is pressed on a line by itself.
The server prefix does not affect the recording of values into the value
history; to print a value without recording it into the value history,
use the output command instead of the print command.
When gdb prompts for input, it annotates this fact so it is possible to know when to send output, when the output from a given command is over, etc.
Different kinds of input each have a different input type. Each
input type has three annotations: a pre- annotation, which
denotes the beginning of any prompt which is being output, a plain
annotation, which denotes the end of the prompt, and then a post-
annotation which denotes the end of any echo which may (or may not) be
associated with the input. For example, the prompt input type
features the following annotations:
^Z^Zpre-prompt
^Z^Zprompt
^Z^Zpost-prompt
promptcommandscommands
command. The annotations are repeated for each command which is input.
overload-choicequeryprompt-for-continueset height 0 to disable
prompting. This is because the counting of lines is buggy in the
presence of annotations.
^Z^Zquit
This annotation occurs right before gdb responds to an interrupt.
^Z^Zerror
This annotation occurs right before gdb responds to an error.
Quit and error annotations indicate that any annotations which gdb was
in the middle of may end abruptly. For example, if a
value-history-begin annotation is followed by a error, one
cannot expect to receive the matching value-history-end. One
cannot expect not to receive it either, however; an error annotation
does not necessarily mean that gdb is immediately returning all the way
to the top level.
A quit or error annotation may be preceded by
^Z^Zerror-begin
Any output between that and the quit or error annotation is the error message.
Warning messages are not yet annotated.
The following annotations say that certain pieces of state may have changed.
^Z^Zframes-invalidbacktrace command) may
have changed.
^Z^Zbreakpoints-invalid
When the program starts executing due to a gdb command such as
step or continue,
^Z^Zstarting
is output. When the program stops,
^Z^Zstopped
is output. Before the stopped annotation, a variety of
annotations describe how the program stopped.
^Z^Zexited exit-status^Z^Zsignalled^Z^Zsignalled, the
annotation continues:
intro-text
^Z^Zsignal-name
name
^Z^Zsignal-name-end
middle-text
^Z^Zsignal-string
string
^Z^Zsignal-string-end
end-text
where name is the name of the signal, such as SIGILL or
SIGSEGV, and string is the explanation of the signal, such
as Illegal Instruction or Segmentation fault.
intro-text, middle-text, and end-text are for the
user's benefit and have no particular format.
^Z^Zsignalsignalled, but gdb is
just saying that the program received the signal, not that it was
terminated with it.
^Z^Zbreakpoint number^Z^Zwatchpoint numberThe following annotation is used instead of displaying source code:
^Z^Zsource filename:line:character:middle:addr
where filename is an absolute file name indicating which source file, line is the line number within that file (where 1 is the first line in the file), character is the character position within the file (where 0 is the first character in the file) (for most debug formats this will necessarily point to the beginning of a line), middle is `middle' if addr is in the middle of the line, or `beg' if addr is at the beginning of the line, and addr is the address in the target program associated with the source which is being displayed. addr is in the form `0x' followed by one or more lowercase hex digits (note that this does not depend on the language).
Your bug reports play an essential role in making gdb reliable.
Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of gdb work better. Bug reports are your contribution to the maintenance of gdb.
In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug.
If you are not sure whether you have found a bug, here are some guidelines:
A number of companies and individuals offer support for gnu products. If you obtained gdb from a support organization, we recommend you contact that organization first.
You can find contact information for many support companies and individuals in the file etc/SERVICE in the gnu Emacs distribution.
In any event, we also recommend that you submit bug reports for gdb. The prefered method is to submit them directly using gdb's Bugs web page. Alternatively, the e-mail gateway can be used.
Do not send bug reports to `info-gdb', or to `help-gdb', or to any newsgroups. Most users of gdb do not want to receive bug reports. Those that do have arranged to receive `bug-gdb'.
The mailing list `bug-gdb' has a newsgroup `gnu.gdb.bug' which serves as a repeater. The mailing list and the newsgroup carry exactly the same messages. Often people think of posting bug reports to the newsgroup instead of mailing them. This appears to work, but it has one problem which can be crucial: a newsgroup posting often lacks a mail path back to the sender. Thus, if we need to ask for more information, we may be unable to reach you. For this reason, it is better to send bug reports to the mailing list.
The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it!
Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the debugger into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix the bug. It may be that the bug has been reported previously, but neither you nor we can know that unless your bug report is complete and self-contained.
Sometimes people give a few sketchy facts and ask, “Does this ring a bell?” Those bug reports are useless, and we urge everyone to refuse to respond to them except to chide the sender to report bugs properly.
To enable us to fix the bug, you should include all these things:
show
version.
Without this, we will not know whether there is any point in looking for the bug in the current version of gdb.
gcc --version to get this
information; for other compilers, see the documentation for those
compilers.
If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug.
Of course, if the bug is that gdb gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. You might as well not give us a chance to make a mistake.
Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of gdb is out of synch, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations.
The line numbers in our development sources will not match those in your sources. Your line numbers would convey no useful information to us.
Here are some things that are not necessary:
Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.
This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else.
Of course, if you can find a simpler example to report instead of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, and so on.
However, simplification is not vital; if you do not want to do this, report the bug anyway and send us the entire test case you used.
A patch for the bug does help us if it is a good one. But do not omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all.
Sometimes with a program as complicated as gdb it is very hard to construct an example that will make the program follow a certain path through the code. If you do not send us the example, we will not be able to construct one, so we will not be able to verify that the bug is fixed.
And if we cannot understand what bug you are trying to fix, or why your patch should be an improvement, we will not install it. A test case will help us to understand.
Such guesses are usually wrong. Even we cannot guess right about such things without first using the debugger to find the facts.
This chapter describes the basic features of the gnu command line editing interface.
The following paragraphs describe the notation used to represent keystrokes.
The text C-k is read as `Control-K' and describes the character produced when the <k> key is pressed while the Control key is depressed.
The text M-k is read as `Meta-K' and describes the character produced when the Meta key (if you have one) is depressed, and the <k> key is pressed. The Meta key is labeled <ALT> on many keyboards. On keyboards with two keys labeled <ALT> (usually to either side of the space bar), the <ALT> on the left side is generally set to work as a Meta key. The <ALT> key on the right may also be configured to work as a Meta key or may be configured as some other modifier, such as a Compose key for typing accented characters.
If you do not have a Meta or <ALT> key, or another key working as a Meta key, the identical keystroke can be generated by typing <ESC> first, and then typing <k>. Either process is known as metafying the <k> key.
The text M-C-k is read as `Meta-Control-k' and describes the character produced by metafying C-k.
In addition, several keys have their own names. Specifically, <DEL>, <ESC>, <LFD>, <SPC>, <RET>, and <TAB> all stand for themselves when seen in this text, or in an init file (see Readline Init File). If your keyboard lacks a <LFD> key, typing <C-j> will produce the desired character. The <RET> key may be labeled <Return> or <Enter> on some keyboards.
Often during an interactive session you type in a long line of text, only to notice that the first word on the line is misspelled. The Readline library gives you a set of commands for manipulating the text as you type it in, allowing you to just fix your typo, and not forcing you to retype the majority of the line. Using these editing commands, you move the cursor to the place that needs correction, and delete or insert the text of the corrections. Then, when you are satisfied with the line, you simply press <RET>. You do not have to be at the end of the line to press <RET>; the entire line is accepted regardless of the location of the cursor within the line.
In order to enter characters into the line, simply type them. The typed character appears where the cursor was, and then the cursor moves one space to the right. If you mistype a character, you can use your erase character to back up and delete the mistyped character.
Sometimes you may mistype a character, and not notice the error until you have typed several other characters. In that case, you can type C-b to move the cursor to the left, and then correct your mistake. Afterwards, you can move the cursor to the right with C-f.
When you add text in the middle of a line, you will notice that characters to the right of the cursor are `pushed over' to make room for the text that you have inserted. Likewise, when you delete text behind the cursor, characters to the right of the cursor are `pulled back' to fill in the blank space created by the removal of the text. A list of the bare essentials for editing the text of an input line follows.
(Depending on your configuration, the <Backspace> key be set to delete the character to the left of the cursor and the <DEL> key set to delete the character underneath the cursor, like C-d, rather than the character to the left of the cursor.)
The above table describes the most basic keystrokes that you need in order to do editing of the input line. For your convenience, many other commands have been added in addition to C-b, C-f, C-d, and <DEL>. Here are some commands for moving more rapidly about the line.
Notice how C-f moves forward a character, while M-f moves forward a word. It is a loose convention that control keystrokes operate on characters while meta keystrokes operate on words.
Killing text means to delete the text from the line, but to save it away for later use, usually by yanking (re-inserting) it back into the line. (`Cut' and `paste' are more recent jargon for `kill' and `yank'.)
If the description for a command says that it `kills' text, then you can be sure that you can get the text back in a different (or the same) place later.
When you use a kill command, the text is saved in a kill-ring. Any number of consecutive kills save all of the killed text together, so that when you yank it back, you get it all. The kill ring is not line specific; the text that you killed on a previously typed line is available to be yanked back later, when you are typing another line. Here is the list of commands for killing text.
Here is how to yank the text back into the line. Yanking means to copy the most-recently-killed text from the kill buffer.
You can pass numeric arguments to Readline commands. Sometimes the argument acts as a repeat count, other times it is the sign of the argument that is significant. If you pass a negative argument to a command which normally acts in a forward direction, that command will act in a backward direction. For example, to kill text back to the start of the line, you might type `M-- C-k'.
The general way to pass numeric arguments to a command is to type meta digits before the command. If the first `digit' typed is a minus sign (`-'), then the sign of the argument will be negative. Once you have typed one meta digit to get the argument started, you can type the remainder of the digits, and then the command. For example, to give the C-d command an argument of 10, you could type `M-1 0 C-d', which will delete the next ten characters on the input line.
Readline provides commands for searching through the command history for lines containing a specified string. There are two search modes: incremental and non-incremental.
Incremental searches begin before the user has finished typing the
search string.
As each character of the search string is typed, Readline displays
the next entry from the history matching the string typed so far.
An incremental search requires only as many characters as needed to
find the desired history entry.
To search backward in the history for a particular string, type
C-r. Typing C-s searches forward through the history.
The characters present in the value of the isearch-terminators variable
are used to terminate an incremental search.
If that variable has not been assigned a value, the <ESC> and
C-J characters will terminate an incremental search.
C-g will abort an incremental search and restore the original line.
When the search is terminated, the history entry containing the
search string becomes the current line.
To find other matching entries in the history list, type C-r or C-s as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a Readline command will terminate the search and execute that command. For instance, a <RET> will terminate the search and accept the line, thereby executing the command from the history list. A movement command will terminate the search, make the last line found the current line, and begin editing.
Readline remembers the last incremental search string. If two C-rs are typed without any intervening characters defining a new search string, any remembered search string is used.
Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line.
Although the Readline library comes with a set of Emacs-like keybindings installed by default, it is possible to use a different set of keybindings. Any user can customize programs that use Readline by putting commands in an inputrc file, conventionally in his home directory. The name of this file is taken from the value of the environment variable INPUTRC. If that variable is unset, the default is ~/.inputrc.
When a program which uses the Readline library starts up, the init file is read, and the key bindings are set.
In addition, the C-x C-r command re-reads this init file, thus
incorporating any changes that you might have made to it.
There are only a few basic constructs allowed in the Readline init file. Blank lines are ignored. Lines beginning with a `#' are comments. Lines beginning with a `$' indicate conditional constructs (see Conditional Init Constructs). Other lines denote variable settings and key bindings.
set command within the init file.
The syntax is simple:
set variable value
Here, for example, is how to
change from the default Emacs-like key binding to use
vi line editing commands:
set editing-mode vi
Variable names and values, where appropriate, are recognized without regard to case.
A great deal of run-time behavior is changeable with the following variables.
bell-stylecomment-begininsert-comment command is executed. The default value
is "#".
completion-ignore-casecompletion-query-items100.
convert-metadisable-completionself-insert. The default is `off'.
editing-modeediting-mode variable controls which default set of
key bindings is used. By default, Readline starts up in Emacs editing
mode, where the keystrokes are most similar to Emacs. This variable can be
set to either `emacs' or `vi'.
enable-keypadexpand-tildeIf set to `on', the history code attempts to place point at the
same location on each history line retrived with previous-history
or next-history.
horizontal-scroll-modeinput-metameta-flag is a
synonym for this variable.
isearch-terminatorskeymapkeymap names are
emacs,
emacs-standard,
emacs-meta,
emacs-ctlx,
vi,
vi-move,
vi-command, and
vi-insert.
vi is equivalent to vi-command; emacs is
equivalent to emacs-standard. The default value is emacs.
The value of the editing-mode variable also affects the
default keymap.
mark-directoriesmark-modified-linesmark-symlinked-directoriesmark-directories).
The default is `off'.
match-hidden-filesoutput-metapage-completionsmore-like pager
to display a screenful of possible completions at a time.
This variable is `on' by default.
print-completions-horizontallyshow-all-if-ambiguousvisible-statsOnce you know the name of the command, simply place on a line in the init file the name of the key you wish to bind the command to, a colon, and then the name of the command. The name of the key can be expressed in different ways, depending on what you find most comfortable.
In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).
Control-u: universal-argument
Meta-Rubout: backward-kill-word
Control-o: "> output"
In the above example, C-u is bound to the function
universal-argument,
M-DEL is bound to the function backward-kill-word, and
C-o is bound to run the macro
expressed on the right hand side (that is, to insert the text
`> output' into the line).
A number of symbolic character names are recognized while
processing this key binding syntax:
DEL,
ESC,
ESCAPE,
LFD,
NEWLINE,
RET,
RETURN,
RUBOUT,
SPACE,
SPC,
and
TAB.
"\C-u": universal-argument
"\C-x\C-r": re-read-init-file
"\e[11~": "Function Key 1"
In the above example, C-u is again bound to the function
universal-argument (just as it was in the first example),
`C-x C-r' is bound to the function re-read-init-file,
and `<ESC> <[> <1> <1> <~>' is bound to insert
the text `Function Key 1'.
The following gnu Emacs style escape sequences are available when specifying key sequences:
In addition to the gnu Emacs style escape sequences, a second set of backslash escapes is available:
\a\b\d\f\n\r\t\v\nnn\xHHWhen entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including `"' and `''. For example, the following binding will make `C-x \' insert a single `\' into the line:
"\C-x\\": "\\"
Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests. There are four parser directives used.
$if$if construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
Readline. The text of the test extends to the end of the line;
no characters are required to isolate it.
modemode= form of the $if directive is used to test
whether Readline is in emacs or vi mode.
This may be used in conjunction
with the `set keymap' command, for instance, to set bindings in
the emacs-standard and emacs-ctlx keymaps only if
Readline is starting out in emacs mode.
termterm= form may be used to include terminal-specific
key bindings, perhaps to bind the key sequences output by the
terminal's function keys. The word on the right side of the
`=' is tested against both the full name of the terminal and
the portion of the terminal name before the first `-'. This
allows sun to match both sun and sun-cmd,
for instance.
application $if Bash
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
$endif
$endif$if command.
$else$if directive are executed if
the test fails.
$include $include /etc/inputrc
Here is an example of an inputrc file. This illustrates key binding, variable assignment, and conditional syntax.
# This file controls the behaviour of line input editing for
# programs that use the GNU Readline library. Existing
# programs include FTP, Bash, and GDB.
#
# You can re-read the inputrc file with C-x C-r.
# Lines beginning with '#' are comments.
#
# First, include any systemwide bindings and variable
# assignments from /etc/Inputrc
$include /etc/Inputrc
#
# Set various bindings for emacs mode.
set editing-mode emacs
$if mode=emacs
Meta-Control-h: backward-kill-word Text after the function name is ignored
#
# Arrow keys in keypad mode
#
#"\M-OD": backward-char
#"\M-OC": forward-char
#"\M-OA": previous-history
#"\M-OB": next-history
#
# Arrow keys in ANSI mode
#
"\M-[D": backward-char
"\M-[C": forward-char
"\M-[A": previous-history
"\M-[B": next-history
#
# Arrow keys in 8 bit keypad mode
#
#"\M-\C-OD": backward-char
#"\M-\C-OC": forward-char
#"\M-\C-OA": previous-history
#"\M-\C-OB": next-history
#
# Arrow keys in 8 bit ANSI mode
#
#"\M-\C-[D": backward-char
#"\M-\C-[C": forward-char
#"\M-\C-[A": previous-history
#"\M-\C-[B": next-history
C-q: quoted-insert
$endif
# An old-style binding. This happens to be the default.
TAB: complete
# Macros that are convenient for shell interaction
$if Bash
# edit the path
"\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
# prepare to type a quoted word --
# insert open and close double quotes
# and move to just after the open quote
"\C-x\"": "\"\"\C-b"
# insert a backslash (testing backslash escapes
# in sequences and macros)
"\C-x\\": "\\"
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
# Add a binding to refresh the line, which is unbound
"\C-xr": redraw-current-line
# Edit variable on current line.
"\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
$endif
# use a visible bell if one is available
set bell-style visible
# don't strip characters to 7 bits when reading
set input-meta on
# allow iso-latin1 characters to be inserted rather
# than converted to prefix-meta sequences
set convert-meta off
# display characters with the eighth bit set directly
# rather than as meta-prefixed characters
set output-meta on
# if there are more than 150 possible completions for
# a word, ask the user if he wants to see all of them
set completion-query-items 150
# For FTP
$if Ftp
"\C-xg": "get \M-?"
"\C-xt": "put \M-?"
"\M-.": yank-last-arg
$endif
This section describes Readline commands that may be bound to key sequences. Command names without an accompanying key sequence are unbound by default.
In the following descriptions, point refers to the current cursor
position, and mark refers to a cursor position saved by the
set-mark command.
The text between the point and mark is referred to as the region.
beginning-of-line (C-a)end-of-line (C-e)forward-char (C-f)backward-char (C-b)forward-word (M-f)backward-word (M-b)clear-screen (C-l)redraw-current-line ()accept-line (Newline or Return)add_history().
If this line is a modified history line, the history line is restored
to its original state.
previous-history (C-p)next-history (C-n)beginning-of-history (M-<)end-of-history (M->)reverse-search-history (C-r)forward-search-history (C-s)non-incremental-reverse-search-history (M-p)non-incremental-forward-search-history (M-n)history-search-forward ()history-search-backward ()yank-nth-arg (M-C-y)yank-last-arg (M-. or M-_)yank-nth-arg.
Successive calls to yank-last-arg move back through the history
list, inserting the last argument of each line in turn.
delete-char (C-d)delete-char, then
return eof.
backward-delete-char (Rubout)forward-backward-delete-char ()quoted-insert (C-q or C-v)tab-insert (M-<TAB>)self-insert (a, b, A, 1, !, ...)transpose-chars (C-t)transpose-words (M-t)upcase-word (M-u)downcase-word (M-l)capitalize-word (M-c)overwrite-mode ()emacs mode; vi mode does overwrite differently.
Each call to readline() starts in insert mode.
In overwrite mode, characters bound to self-insert replace
the text at point rather than pushing the text to the right.
Characters bound to backward-delete-char replace the character
before point with a space.
By default, this command is unbound.
kill-line (C-k)backward-kill-line (C-x Rubout)unix-line-discard (C-u)kill-whole-line ()kill-word (M-d)forward-word.
backward-kill-word (M-<DEL>)backward-word.
unix-word-rubout (C-w)delete-horizontal-space ()kill-region ()copy-region-as-kill ()copy-backward-word ()backward-word.
By default, this command is unbound.
copy-forward-word ()forward-word.
By default, this command is unbound.
yank (C-y)yank-pop (M-y)yank or yank-pop.
digit-argument (M-0, M-1, ... M--)universal-argument ()universal-argument
again ends the numeric argument, but is otherwise ignored.
As a special case, if this command is immediately followed by a
character that is neither a digit or minus sign, the argument count
for the next command is multiplied by four.
The argument count is initially one, so executing this function the
first time makes the argument count four, a second time makes the
argument count sixteen, and so on.
By default, this is not bound to a key.
complete (<TAB>)possible-completions (M-?)insert-completions (M-*)possible-completions.
menu-complete ()complete, but replaces the word to be completed
with a single match from the list of possible completions.
Repeated execution of menu-complete steps through the list
of possible completions, inserting each match in turn.
At the end of the list of completions, the bell is rung
(subject to the setting of bell-style)
and the original text is restored.
An argument of n moves n positions forward in the list
of matches; a negative argument may be used to move backward
through the list.
This command is intended to be bound to <TAB>, but is unbound
by default.
delete-char-or-list ()delete-char).
If at the end of the line, behaves identically to
possible-completions.
This command is unbound by default.
start-kbd-macro (C-x ()end-kbd-macro (C-x ))call-last-kbd-macro (C-x e)re-read-init-file (C-x C-r)abort (C-g)bell-style).
do-uppercase-version (M-a, M-b, M-x, ...)prefix-meta (<ESC>)undo (C-_ or C-x C-u)revert-line (M-r)undo
command enough times to get back to the beginning.
tilde-expand (M-~)set-mark (C-@)exchange-point-and-mark (C-x C-x)character-search (C-])character-search-backward (M-C-])insert-comment (M-#)comment-begin
variable is inserted at the beginning of the current line.
If a numeric argument is supplied, this command acts as a toggle: if
the characters at the beginning of the line do not match the value
of comment-begin, the value is inserted, otherwise
the characters in comment-begin are deleted from the beginning of
the line.
In either case, the line is accepted as if a newline had been typed.
dump-functions ()dump-variables ()dump-macros ()emacs-editing-mode (C-e)vi command mode, this causes a switch to emacs
editing mode.
vi-editing-mode (M-C-j)emacs editing mode, this causes a switch to vi
editing mode.
While the Readline library does not have a full set of vi
editing functions, it does contain enough to allow simple editing
of the line. The Readline vi mode behaves as specified in
the posix 1003.2 standard.
In order to switch interactively between emacs and vi
editing modes, use the command M-C-j (bound to emacs-editing-mode
when in vi mode and to vi-editing-mode in emacs mode).
The Readline default is emacs mode.
When you enter a line in vi mode, you are already placed in
`insertion' mode, as if you had typed an `i'. Pressing <ESC>
switches you into `command' mode, where you can edit the text of the
line with the standard vi movement keys, move to previous
history lines with `k' and subsequent lines with `j', and
so forth.
This chapter describes how to use the GNU History Library interactively, from a user's standpoint. It should be considered a user's guide.
The History library provides a history expansion feature that is similar
to the history expansion provided by csh. This section
describes the syntax used to manipulate the history information.
History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly.
History expansion takes place in two parts. The first is to determine which line from the history list should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is called the event, and the portions of that line that are acted upon are called words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion that Bash does, so that several words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is `!' by default.
An event designator is a reference to a command line entry in the history list.
!!n!-n!!!string!?string[?]^string1^string2^!!:s/string1/string2/.
!#Word designators are used to select desired words from the event. A `:' separates the event specification from the word designator. It may be omitted if the word designator begins with a `^', `$', `*', `-', or `%'. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.
For example,
!!!!:$!$.
!fi:2fi.
Here are the word designators:
0 (zero)0th word. For many applications, this is the command word.
^$%-y*0th. This is a synonym for `1-$'.
It is not an error to use `*' if there is just one word in the event;
the empty string is returned in that case.
*-If a word designator is supplied without an event specification, the previous command is used as the event.
After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a `:'.
htreps/old/new/&ggs/old/new/,
or with `&'.
The gdb 4 release includes an already-formatted reference card, ready for printing with PostScript or Ghostscript, in the gdb subdirectory of the main source directory8. If you can use PostScript or Ghostscript with your printer, you can print the reference card immediately with refcard.ps.
The release also includes the source for the reference card. You can format it, using TeX, by typing:
make refcard.dvi
The gdb reference card is designed to print in landscape mode on US “letter” size paper; that is, on a sheet 11 inches wide by 8.5 inches high. You will need to specify this form of printing as an option to your dvi output program.
All the documentation for gdb comes as part of the machine-readable
distribution. The documentation is written in Texinfo format, which is
a documentation system that uses a single source file to produce both
on-line information and a printed manual. You can use one of the Info
formatting commands to create the on-line version of the documentation
and TeX (or texi2roff) to typeset the printed version.
gdb includes an already formatted copy of the on-line Info
version of this manual in the gdb subdirectory. The main Info
file is gdb-6.1/gdb/gdb.info, and it refers to
subordinate files matching `gdb.info*' in the same directory. If
necessary, you can print out these files, or read them with any editor;
but they are easier to read using the info subsystem in gnu
Emacs or the standalone info program, available as part of the
gnu Texinfo distribution.
If you want to format these Info files yourself, you need one of the
Info formatting programs, such as texinfo-format-buffer or
makeinfo.
If you have makeinfo installed, and are in the top level
gdb source directory (gdb-6.1, in the case of
version 6.1), you can make the Info file by typing:
cd gdb
make gdb.info
If you want to typeset and print copies of this manual, you need TeX, a program to print its dvi output files, and texinfo.tex, the Texinfo definitions file.
TeX is a typesetting program; it does not print files directly, but produces output files called dvi files. To print a typeset document, you need a program to print dvi files. If your system has TeX installed, chances are it has such a program. The precise command to use depends on your system; lpr -d is common; another (for PostScript devices) is dvips. The dvi print command may require a file name without any extension or a `.dvi' extension.
TeX also requires a macro definitions file called texinfo.tex. This file tells TeX how to typeset a document written in Texinfo format. On its own, TeX cannot either read or typeset a Texinfo file. texinfo.tex is distributed with GDB and is located in the gdb-version-number/texinfo directory.
If you have TeX and a dvi printer program installed, you can typeset and print this manual. First switch to the the gdb subdirectory of the main source directory (for example, to gdb-6.1/gdb) and type:
make gdb.dvi
Then give gdb.dvi to your dvi printing program.
gdb comes with a configure script that automates the process
of preparing gdb for installation; you can then use make to
build the gdb program.
The gdb distribution includes all the source code you need for gdb in a single directory, whose name is usually composed by appending the version number to `gdb'.
For example, the gdb version 6.1 distribution is in the gdb-6.1 directory. That directory contains:
gdb-6.1/configure (and supporting files)gdb-6.1/gdbgdb-6.1/bfdgdb-6.1/includegdb-6.1/libibertygdb-6.1/opcodesgdb-6.1/readlinegdb-6.1/globgdb-6.1/mmallocThe simplest way to configure and build gdb is to run configure
from the gdb-version-number source directory, which in
this example is the gdb-6.1 directory.
First switch to the gdb-version-number source directory
if you are not already in it; then run configure. Pass the
identifier for the platform on which gdb will run as an
argument.
For example:
cd gdb-6.1
./configure host
make
where host is an identifier such as `sun4' or
`decstation', that identifies the platform where gdb will run.
(You can often leave off host; configure tries to guess the
correct value by examining your system.)
Running `configure host' and then running make builds the
bfd, readline, mmalloc, and libiberty
libraries, then gdb itself. The configured source files, and the
binaries, are left in the corresponding source directories.
configure is a Bourne-shell (/bin/sh) script; if your
system does not recognize this automatically when you run a different
shell, you may need to run sh on it explicitly:
sh configure host
If you run configure from a directory that contains source
directories for multiple libraries or programs, such as the
gdb-6.1 source directory for version 6.1, configure
creates configuration files for every directory level underneath (unless
you tell it not to, with the `--norecursion' option).
You should run the configure script from the top directory in the
source tree, the gdb-version-number directory. If you run
configure from one of the subdirectories, you will configure only
that subdirectory. That is usually not what you want. In particular,
if you run the first configure from the gdb subdirectory
of the gdb-version-number directory, you will omit the
configuration of bfd, readline, and other sibling
directories of the gdb subdirectory. This leads to build errors
about missing include files such as bfd/bfd.h.
You can install gdb anywhere; it has no hardwired paths.
However, you should make sure that the shell on your path (named by
the `SHELL' environment variable) is publicly readable. Remember
that gdb uses the shell to start your program—some systems refuse to
let gdb debug child processes whose programs are not readable.
If you want to run gdb versions for several host or target machines,
you need a different gdb compiled for each combination of
host and target. configure is designed to make this easy by
allowing you to generate each configuration in a separate subdirectory,
rather than in the source directory. If your make program
handles the `VPATH' feature (gnu make does), running
make in each of these directories builds the gdb
program specified there.
To build gdb in a separate directory, run configure
with the `--srcdir' option to specify where to find the source.
(You also need to specify a path to find configure
itself from your working directory. If the path to configure
would be the same as the argument to `--srcdir', you can leave out
the `--srcdir' option; it is assumed.)
For example, with version 6.1, you can build gdb in a separate directory for a Sun 4 like this:
cd gdb-6.1
mkdir ../gdb-sun4
cd ../gdb-sun4
../gdb-6.1/configure sun4
make
When configure builds a configuration using a remote source
directory, it creates a tree for the binaries with the same structure
(and using the same names) as the tree under the source directory. In
the example, you'd find the Sun 4 library libiberty.a in the
directory gdb-sun4/libiberty, and gdb itself in
gdb-sun4/gdb.
Make sure that your path to the configure script has just one instance of gdb in it. If your path to configure looks like ../gdb-6.1/gdb/configure, you are configuring only one subdirectory of gdb, not the whole package. This leads to build errors about missing include files such as bfd/bfd.h.
One popular reason to build several gdb configurations in separate
directories is to configure gdb for cross-compiling (where
gdb runs on one machine—the host—while debugging
programs that run on another machine—the target).
You specify a cross-debugging target by
giving the `--target=target' option to configure.
When you run make to build a program or library, you must run
it in a configured directory—whatever directory you were in when you
called configure (or one of its subdirectories).
The Makefile that configure generates in each source
directory also runs recursively. If you type make in a source
directory such as gdb-6.1 (or in a separate configured
directory configured with `--srcdir=dirname/gdb-6.1'), you
will build all the required libraries, and then build GDB.
When you have multiple hosts or targets configured in separate
directories, you can run make on them in parallel (for example,
if they are NFS-mounted on each of the hosts); they will not interfere
with each other.
The specifications used for hosts and targets in the configure
script are based on a three-part naming scheme, but some short predefined
aliases are also supported. The full naming scheme encodes three pieces
of information in the following pattern:
architecture-vendor-os
For example, you can use the alias sun4 as a host argument,
or as the value for target in a --target=target
option. The equivalent full name is `sparc-sun-sunos4'.
The configure script accompanying gdb does not provide
any query facility to list all supported host and target names or
aliases. configure calls the Bourne shell script
config.sub to map abbreviations to full names; you can read the
script, if you wish, or you can use it to test your guesses on
abbreviations—for example:
% sh config.sub i386-linux
i386-pc-linux-gnu
% sh config.sub alpha-linux
alpha-unknown-linux-gnu
% sh config.sub hp9k700
hppa1.1-hp-hpux
% sh config.sub sun4
sparc-sun-sunos4.1.1
% sh config.sub sun3
m68k-sun-sunos4.1.1
% sh config.sub i986v
Invalid configuration `i986v': machine `i986v' not recognized
config.sub is also distributed in the gdb source
directory (gdb-6.1, for version 6.1).
configure optionsHere is a summary of the configure options and arguments that
are most often useful for building gdb. configure also has
several other options not listed here. see What Configure Does, for a full explanation of configure.
configure [--help] [--prefix=dir] [--exec-prefix=dir] [--srcdir=dirname] [--norecursion] [--rm] [--target=target] host
You may introduce options with a single `-' rather than `--' if you prefer; but you may abbreviate option names if you use `--'.
--helpconfigure.
--prefix=dir--exec-prefix=dir--srcdir=dirnamemake, or another
make that implements the VPATH feature.configure writes configuration specific files in
the current directory, but arranges for them to use the source in the
directory dirname. configure creates directories under
the working directory in parallel to the source directories below
dirname.
--norecursionconfigure is executed; do not
propagate configuration to subdirectories.
--target=targetThere is no convenient way to generate a list of all available targets.
...There is no convenient way to generate a list of all available hosts.
There are many other options available as well, but they are generally needed for special purposes only.
In addition to commands intended for gdb users, gdb includes a number of commands intended for gdb developers. These commands are provided here for reference.
maint info breakpointsbreakpointwatchpointlongjmplongjmp calls.
longjmp resumelongjmp.
untiluntil command.
finishfinish command.
shlib eventsmaint internal-errormaint internal-warninginternal_error
or internal_warning and hence behave as though an internal error
or internal warning has been detected. In addition to reporting the
internal problem, these functions give the user the opportunity to
either quit gdb or create a core file of the current
gdb session.
(gdb) maint internal-error testing, 1, 2
.../maint.c:121: internal-error: testing, 1, 2
A problem internal to GDB has been detected. Further
debugging may prove unreliable.
Quit this debugging session? (y or n) n
Create a core file? (y or n) n
(gdb)
Takes an optional parameter that is used as the text of the error or warning message.
maint print dummy-frames (gdb) b add
...
(gdb) print add(2,3)
Breakpoint 2, add (a=2, b=3) at ...
58 return (a + b);
The program being debugged stopped while in a function called from GDB.
...
(gdb) maint print dummy-frames
0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6
top=0x0200bdd4 id={stack=0x200bddc,code=0x101405c}
call_lo=0x01014000 call_hi=0x01014001
(gdb)
Takes an optional file parameter.
maint print registersmaint print raw-registersmaint print cooked-registersmaint print register-groupsThe command maint print raw-registers includes the contents of
the raw register cache; the command maint print cooked-registers
includes the (cooked) value of all registers; and the command
maint print register-groups includes the groups that each
register is a member of. See Registers.
Takes an optional file parameter.
maint print reggroupsTakes an optional file parameter.
(gdb) maint print reggroups
Group Type
general user
float user
all user
vector user
system user
save internal
restore internal
maint set profilemaint show profileProfiling will be disabled until you use the `maint set profile' command to enable it. When you enable profiling, the system will begin collecting timing and execution count data; when you disable profiling or exit gdb, the results will be written to a log file. Remember that if you use profiling, gdb will overwrite the profiling log file (often called gmon.out). If you have a record of important profiling data in a gmon.out file, be sure to move it to a safe location.
Configuring with `--enable-profiling' arranges for gdb to be compiled with the `-pg' compiler option.
There may be occasions when you need to know something about the protocol—for example, if there is only one serial port to your target machine, you might want your program to do something special if it recognizes a packet meant for gdb.
In the examples below, `->' and `<-' are used to indicate transmitted and received data respectfully.
All gdb commands and responses (other than acknowledgments) are sent as a packet. A packet is introduced with the character `$', the actual packet-data, and the terminating character `#' followed by a two-digit checksum:
$packet-data#checksum
The two-digit checksum is computed as the modulo 256 sum of all characters between the leading `$' and the trailing `#' (an eight bit unsigned checksum).
Implementors should note that prior to gdb 5.0 the protocol specification also included an optional two-digit sequence-id:
$sequence-id:packet-data#checksum
That sequence-id was appended to the acknowledgment. gdb has never output sequence-ids. Stubs that handle packets added since gdb 5.0 must not accept sequence-id.
When either the host or the target machine receives a packet, the first response expected is an acknowledgment: either `+' (to indicate the package was received correctly) or `-' (to request retransmission):
->$packet-data#checksum <-+
The host (gdb) sends commands, and the target (the debugging stub incorporated in your program) sends a response. In the case of step and continue commands, the response is only sent when the operation has completed (the target has again stopped).
packet-data consists of a sequence of characters with the exception of `#' and `$' (see `X' packet for additional exceptions).
Fields within the packet should be separated using `,' `;' or `:'. Except where otherwise noted all numbers are represented in hex with leading zeros suppressed.
Implementors should note that prior to gdb 5.0, the character `:' could not appear as the third character in a packet (as it would potentially conflict with the sequence-id).
Response data can be run-length encoded to save space. A `*'
means that the next character is an ascii encoding giving a repeat count
which stands for that many repetitions of the character preceding the
`*'. The encoding is n+29, yielding a printable character
where n >=3 (which is where rle starts to win). The printable
characters `$', `#', `+' and `-' or with a numeric
value greater than 126 should not be used.
So:
"0* "
means the same as "0000".
The error response returned for some packets includes a two character error number. That number is not well defined.
For any command not supported by the stub, an empty response (`$#00') should be returned. That way it is possible to extend the protocol. A newer gdb can tell if a packet is supported based on that response.
A stub is required to support the `g', `G', `m', `M', `c', and `s' commands. All other commands are optional.
The following table provides a complete list of all currently defined commands and their corresponding response data.
! — extended modeReply:
? — last signalReply:
See Stop Reply Packets, for the reply specifications.
a — reservedAarglen,argnum,arg,... — set program arguments (reserved)gdbserver for more details.
Reply:
bbaud — set baud (deprecated)JTC: When does the transport layer state change? When it's received, or after the ACK is transmitted. In either case, there are problems if the command or the acknowledgment packet is dropped.
Stan: If people really wanted to add something like this, and get
it working for the first time, they ought to modify ser-unix.c to send
some kind of out-of-band message to a specially-setup stub and have the
switch happen "in between" packets, so that from remote protocol's point
of view, nothing actually happened.
Baddr,mode — set breakpoint (deprecated)This packet has been replaced by the `Z' and `z' packets
(see insert breakpoint or watchpoint packet).
caddr — continueReply:
See Stop Reply Packets, for the reply specifications.
Csig;addr — continue with signal;addr is omitted, resume at same address.
Reply:
See Stop Reply Packets, for the reply specifications.
d — toggle debug (deprecated)D — detachdetach command.
Reply:
e — reservedE — reservedf — reservedFRC,EE,CF;XX — Reply to target's F packet.F request packet
sent by the target. This is part of the File-I/O protocol extension.
See File-I/O remote protocol extension, for the specification.
g — read registersReply:
g packets is specified below.
GXX... — write regsReply:
h — reservedHct... — set threadReply:
iaddr,nnn — cycle step (draft),nnn is
present, cycle step nnn cycles. If addr is present, cycle
step starting at that address.
I — signal then cycle step (reserved)j — reservedJ — reservedk — kill requestK — reservedl — reservedL — reservedmaddr,length — read memoryReply:
Maddr,length:XX... — write memReply:
n — reservedN — reservedo — reservedO — reservedpn... — read reg (reserved)Reply:
Pn...=r... — write registerReply:
qquery — general queryReply:
Qvar=val — general setSee general query packet, for a discussion of naming conventions.
r — reset (deprecated)RXX — remote restartReply:
saddr — stepReply:
See Stop Reply Packets, for the reply specifications.
Ssig;addr — step with signalReply:
See Stop Reply Packets, for the reply specifications.
taddr:PP,MM — searchTXX — thread aliveReply:
u — reservedU — reservedv — verbose packet prefixv are identified by a multi-letter name,
up to the first ; or ? (or the end of the packet).
vCont[;action[:tid]]... — extended resumecCsigsSsigThe optional addr argument normally associated with these packets is
not supported in vCont.
Reply:
See Stop Reply Packets, for the reply specifications.
vCont? — extended resume queryvCont packet.
Reply:
vCont[;action]...'vCont packet is supported. Each action is a supported
command in the vCont packet.
vCont packet is not supported.
V — reservedw — reservedW — reservedx — reservedXaddr,length:XX... — write mem (binary)$, #, and 0x7d are
escaped using 0x7d.
Reply:
y — reservedY reservedztype,addr,length — remove breakpoint or watchpoint (draft)Ztype,addr,length — insert breakpoint or watchpoint (draft)Z) or remove (z) a type breakpoint or
watchpoint starting at address address and covering the next
length bytes.
Each breakpoint and watchpoint packet type is documented separately.
Implementation notes: A remote target shall return an empty string
for an unrecognized breakpoint or watchpoint packet type. A
remote target shall support either both or neither of a given
Ztype... and ztype... packet pair. To
avoid potential problems with duplicate packets, the operations should
be implemented in an idempotent way.
z0,addr,length — remove memory breakpoint (draft)Z0,addr,length — insert memory breakpoint (draft)Z0) or remove (z0) a memory breakpoint at address
addr of size length.
A memory breakpoint is implemented by replacing the instruction at
addr with a software breakpoint or trap instruction. The
length is used by targets that indicates the size of the
breakpoint (in bytes) that should be inserted (e.g., the arm and
mips can insert either a 2 or 4 byte breakpoint).
Implementation note: It is possible for a target to copy or move code that contains memory breakpoints (e.g., when implementing overlays). The behavior of this packet, in the presence of such a target, is not defined.
Reply:
z1,addr,length — remove hardware breakpoint (draft)Z1,addr,length — insert hardware breakpoint (draft)Z1) or remove (z1) a hardware breakpoint at
address addr of size length.
A hardware breakpoint is implemented using a mechanism that is not dependant on being able to modify the target's memory.
Implementation note: A hardware breakpoint is not affected by code movement.
Reply:
z2,addr,length — remove write watchpoint (draft)Z2,addr,length — insert write watchpoint (draft)Z2) or remove (z2) a write watchpoint.
Reply:
z3,addr,length — remove read watchpoint (draft)Z3,addr,length — insert read watchpoint (draft)Z3) or remove (z3) a read watchpoint.
Reply:
z4,addr,length — remove access watchpoint (draft)Z4,addr,length — insert access watchpoint (draft)Z4) or remove (z4) an access watchpoint.
Reply:
The `C', `c', `S', `s' and `?' packets can receive any of the below as a reply. In the case of the `C', `c', `S' and `s' packets, that reply is only returned when the target halts. In the below the exact meaning of `signal number' is poorly defined. In general one of the UNIX signal numbering conventions is used.
TAAn...:r...;n...:r...;n...:r...;'DEPRECATED_REGISTER_RAW_SIZE; n... = `thread',
r... = thread process ID, this is a hex integer; n... =
(`watch' | `rwatch' | `awatch', r... = data
address, this is a hex integer; n... = other string not starting
with valid hex digit. gdb should ignore this n...,
r... pair and go on to the next. This way we can extend the
protocol.
,parameter...'parameter... is a list of parameters as defined for this very system call.
The target replies with this packet when it expects gdb to call
a host system call on behalf of the target. gdb replies with
an appropriate F packet and keeps up waiting for the next reply
packet from the target. The latest `C', `c', `S' or
`s' action is expected to be continued.
See File-I/O remote protocol extension, for more details.
The following set and query packets have already been defined.
qC — current threadReply:
QCpid'qfThreadInfo – all thread idsqsThreadInfo
Obtain a list of active thread ids from the target (OS). Since there
may be too many active threads to fit into one reply packet, this query
works iteratively: it may require more than one query/reply sequence to
obtain the entire list of threads. The first query of the sequence will
be the qfThreadInfo query; subsequent queries in the
sequence will be the qsThreadInfo query.
NOTE: replaces the qL query (see below).
Reply:
mid'mid,id...'l'In response to each query, the target will reply with a list of one or
more thread ids, in big-endian hex, separated by commas. gdb
will respond to each reply with a request for more thread ids (using the
qs form of the query), until the target responds with l
(lower-case el, for 'last').
qThreadExtraInfo,id — extra thread infoReply:
qLstartflagthreadcountnextthread — query LIST or threadLIST (deprecated)NOTE: this query is replaced by the qfThreadInfo query
(see above).
Reply:
qMcountdoneargthreadthread...'remote.c:parse_threadlist_response().
qCRC:addr,length — compute CRC of memory blockENN'CCRC32'qOffsets — query sect offsBss offset is included in the
response, gdb ignores this and instead applies the Data
offset to the Bss section.
Reply:
Text=xxx;Data=yyy;Bss=zzz'qPmodethreadid — thread info requestReply:
See remote.c:remote_unpack_thread_info_response().
qRcmd,command — remote commandOoutput console output packets.
Implementors should note that providing access to a stubs's
interpreter may have security implications.
Reply:
ENN'qSymbol:: — symbol lookupReply:
OK'qSymbol:sym_name'qSymbol:sym_value:sym_name message, described below.
qSymbol:sym_value:sym_name — symbol valuesym_name (hex encoded) is the name of a symbol whose value the target has previously requested.
sym_value (hex) is the value for symbol sym_name. If gdb cannot supply a value for sym_name, then this field will be empty.
Reply:
OK'qSymbol:sym_name'qPart:object:read:annex:offset,length — read special dataobject.
Request length bytes starting at offset bytes into the data.
The content and encoding of annex is specific to the object;
it can supply additional details about what data to access.
Here are the specific requests of this form defined so far.
All `qPart:object:read:...'
requests use the same reply formats, listed below.
qPart:auxv:read::offset,lengthReply:
OKE00Ennerrno value.
"" (empty)qPart:object:write:annex:offset:data...object,
starting at offset bytes into the data.
data... is the hex-encoded data to be written.
The content and encoding of annex is specific to the object;
it can supply additional details about what data to access.
No requests of this form are presently in use. This specification serves as a placeholder to document the common format that new specific request specifications ought to use.
Reply:
E00Ennerrno value.
"" (empty)qPart:object:operation:...The following `g'/`G' packets have previously been defined. In the below, some thirty-two bit registers are transferred as sixty-four bits. Those registers should be zero/sign extended (which?) to fill the space allocated. Register bytes are transfered in target byte order. The two nibbles within a register byte are transfered most-significant - least-significant.
sr). The ordering is the same
as MIPS32.
Example sequence of a target being re-started. Notice how the restart does not get any direct output:
->R00<-+target restarts ->?<-+<-T001:1234123412341234->+
Example sequence of a target being stepped by a single instruction:
->G1445...<-+->s<-+time passes <-T001:1234123412341234->+->g<-+<-1455...->+
The File I/O remote protocol extension (short: File-I/O) allows the target to use the hosts file system and console I/O when calling various system calls. System calls on the target system are translated into a remote protocol packet to the host system which then performs the needed actions and returns with an adequate response packet to the target system. This simulates file system operations even on targets that lack file systems.
The protocol is defined host- and target-system independent. It uses it's own independent representation of datatypes and values. Both, gdb and the target's gdb stub are responsible for translating the system dependent values into the unified protocol values when data is transmitted.
The communication is synchronous. A system call is possible only when GDB is waiting for the `C', `c', `S' or `s' packets. While gdb handles the request for a system call, the target is stopped to allow deterministic access to the target's memory. Therefore File-I/O is not interuptible by target signals. It is possible to interrupt File-I/O by a user interrupt (Ctrl-C), though.
The target's request to perform a host system call does not finish the latest `C', `c', `S' or `s' action. That means, after finishing the system call, the target returns to continuing the previous activity (continue, step). No additional continue or step request from gdb is required.
(gdb) continue
<- target requests 'system call X'
target is stopped, gdb executes system call
-> GDB returns result
... target continues, GDB returns to wait for the target
<- target hits breakpoint and sends a Txx packet
The protocol is only used for files on the host file system and for I/O on the console. Character or block special devices, pipes, named pipes or sockets or any other communication method on the host system are not supported by this protocol.
The File-I/O protocol uses the F packet, as request as well
as as reply packet. Since a File-I/O system call can only occur when
gdb is waiting for the continuing or stepping target, the
File-I/O request is a reply that gdb has to expect as a result
of a former `C', `c', `S' or `s' packet.
This F packet contains all information needed to allow gdb
to call the appropriate host system call:
At that point gdb has to perform the following actions.
m packet request. This additional communication has to be
expected by the target implementation and is handled as any other m
packet.
M or X packet. This packet has to be expected
by the target implementation and is handled as any other M or X
packet.
Eventually gdb replies with another F packet which contains all
necessary information for the target to continue. This at least contains
errno, if has been changed by the system call.
After having done the needed type and value coercion, the target continues the latest continue or step action.
F request packet
The F request packet has the following format:
Fcall-id,parameter...
call-id is the identifier to indicate the host system call to be called. This is just the name of the function.
parameter... are the parameters to the system call.
Parameters are hexadecimal integer values, either the real values in case of scalar datatypes, as pointers to target buffer space in case of compound datatypes and unspecified memory areas or as pointer/length pairs in case of string parameters. These are appended to the call-id, each separated from its predecessor by a comma. All values are transmitted in ASCII string representation, pointer/length pairs separated by a slash.
F reply packet
The F reply packet has the following format:
Fretcode,errno,Ctrl-C flag;call specific attachment
retcode is the return code of the system call as hexadecimal value.
errno is the errno set by the call, in protocol specific representation. This parameter can be omitted if the call was successful.
Ctrl-C flag is only send if the user requested a break. In this case, errno must be send as well, even if the call was successful. The Ctrl-C flag itself consists of the character 'C':
F0,0,C
or, if the call was interupted before the host call has been performed:
F-1,4,C
assuming 4 is the protocol specific representation of EINTR.
Structured data which is transferred using a memory read or write as e.g.
a struct stat is expected to be in a protocol specific format with
all scalar multibyte datatypes being big endian. This should be done by
the target before the F packet is sent resp. by gdb before
it transfers memory to the target. Transferred pointers to structured
data should point to the already coerced data at any time.
A special case is, if the Ctrl-C flag is set in the gdb
reply packet. In this case the target should behave, as if it had
gotten a break message. The meaning for the target is “system call
interupted by SIGINT”. Consequentially, the target should actually stop
(as with a break message) and return to gdb with a T02
packet. In this case, it's important for the target to know, in which
state the system call was interrupted. Since this action is by design
not an atomic operation, we have to differ between two cases:
These two states can be distinguished by the target by the value of the
returned errno. If it's the protocol representation of EINTR, the system
call hasn't been performed. This is equivalent to the EINTR handling
on POSIX systems. In any other case, the target may presume that the
system call has been finished — successful or not — and should behave
as if the break message arrived right after the system call.
gdb must behave reliable. If the system call has not been called
yet, gdb may send the F reply immediately, setting EINTR as
errno in the packet. If the system call on the host has been finished
before the user requests a break, the full action must be finshed by
gdb. This requires sending M or X packets as they fit.
The F packet may only be send when either nothing has happened
or the full action has been completed.
By default and if not explicitely closed by the target system, the file
descriptors 0, 1 and 2 are connected to the gdb console. Output
on the gdb console is handled as any other file output operation
(write(1, ...) or write(2, ...)). Console input is handled
by gdb so that after the target read request from file descriptor
0 all following typing is buffered until either one of the following
conditions is met:
read
system call is treated as finished.
If the user has typed more characters as fit in the buffer given to
the read call, the trailing characters are buffered in gdb until
either another read(0, ...) is requested by the target or debugging
is stopped on users request.
A special case in this protocol is the library call isatty which
is implemented as it's own call inside of this protocol. It returns
1 to the target if the file descriptor given as parameter is attached
to the gdb console, 0 otherwise. Implementing through system calls
would require implementing ioctl and would be more complex than
needed.
The other special case in this protocol is the system call which
is implemented as it's own call, too. gdb is taking over the full
task of calling the necessary host calls to perform the system
call. The return value of system is simplified before it's returned
to the target. Basically, the only signal transmitted back is EINTR
in case the user pressed Ctrl-C. Otherwise the return value consists
entirely of the exit status of the called command.
Due to security concerns, the system call is refused to be called
by gdb by default. The user has to allow this call explicitly by
entering
set remote system-call-allowed 1'Disabling the system call is done by
set remote system-call-allowed 0'The current setting is shown by typing
show remote system-call-allowed'
Synopsis:
int open(const char *pathname, int flags); int open(const char *pathname, int flags, mode_t mode);
Request:
Fopen,pathptr/len,flags,mode
flags is the bitwise or of the following values:
O_CREATO_EXCLO_TRUNCO_APPENDO_RDONLYO_WRONLYO_RDWREach other bit is silently ignored.
mode is the bitwise or of the following values:
S_IRUSRS_IWUSRS_IRGRPS_IWGRPS_IROTHS_IWOTHEach other bit is silently ignored.
Return value:
open returns the new file descriptor or -1 if an error occured.
Errors:
EEXISTEISDIREACCESENAMETOOLONGENOENTENODEVEROFSEFAULTENOSPCEMFILEENFILEEINTR
Synopsis:
int close(int fd);
Request:
Fclose,fd
Return value:
close returns zero on success, or -1 if an error occurred.
Errors:
EBADFEINTR
Synopsis:
int read(int fd, void *buf, unsigned int count);
Request:
Fread,fd,bufptr,count
Return value:
On success, the number of bytes read is returned. Zero indicates end of file. If count is zero, read returns zero as well. On error, -1 is returned.
Errors:
EBADFEFAULTEINTR
Synopsis:
int write(int fd, const void *buf, unsigned int count);
Request:
Fwrite,fd,bufptr,count
Return value:
On success, the number of bytes written are returned. Zero indicates nothing was written. On error, -1 is returned.
Errors:
EBADFEFAULTEFBIGENOSPCEINTR
Synopsis:
long lseek (int fd, long offset, int flag);
Request:
Flseek,fd,offset,flag
flag is one of:
SEEK_SETSEEK_CURSEEK_END
Return value:
On success, the resulting unsigned offset in bytes from the beginning of the file is returned. Otherwise, a value of -1 is returned.
Errors:
EBADFESPIPEEINVALEINTR
Synopsis:
int rename(const char *oldpath, const char *newpath);
Request:
Frename,oldpathptr/len,newpathptr/len
Return value:
On success, zero is returned. On error, -1 is returned.
Errors:
EISDIREEXISTEBUSYEINVALENOTDIREFAULTEACCESENAMETOOLONGENOENTEROFSENOSPCEINTR
Synopsis:
int unlink(const char *pathname);
Request:
Funlink,pathnameptr/len
Return value:
On success, zero is returned. On error, -1 is returned.
Errors:
EACCESEPERMEBUSYEFAULTENAMETOOLONGENOENTENOTDIREROFSEINTR
Synopsis:
int stat(const char *pathname, struct stat *buf); int fstat(int fd, struct stat *buf);
Request:
Fstat,pathnameptr/len,bufptr Ffstat,fd,bufptr
Return value:
On success, zero is returned. On error, -1 is returned.
Errors:
EBADFENOENTENOTDIREFAULTEACCESENAMETOOLONGEINTR
Synopsis:
int gettimeofday(struct timeval *tv, void *tz);
Request:
Fgettimeofday,tvptr,tzptr
Return value:
On success, 0 is returned, -1 otherwise.
Errors:
EINVALEFAULT
Synopsis:
int isatty(int fd);
Request:
Fisatty,fd
Return value:
Returns 1 if fd refers to the gdb console, 0 otherwise.
Errors:
EINTR
Synopsis:
int system(const char *command);
Request:
Fsystem,commandptr/len
Return value:
The value returned is -1 on error and the return status of the command otherwise. Only the exit status of the command is returned, which is extracted from the hosts system return value by calling WEXITSTATUS(retval). In case /bin/sh could not be executed, 127 is returned.
Errors:
EINTRThe integral datatypes used in the system calls are
int, unsigned int, long, unsigned long, mode_t and time_t
Int, unsigned int, mode_t and time_t are
implemented as 32 bit values in this protocol.
Long and unsigned long are implemented as 64 bit types.
See Limits, for corresponding MIN and MAX values (similar to those in limits.h) to allow range checking on host and target.
time_t datatypes are defined as seconds since the Epoch.
All integral datatypes transferred as part of a memory read or write of a
structured datatype e.g. a struct stat have to be given in big endian
byte order.
Pointers to target data are transmitted as they are. An exception is made for pointers to buffers for which the length isn't transmitted as part of the function call, namely strings. Strings are transmitted as a pointer/length pair, both as hex values, e.g.
1aaf/12
which is a pointer to data of length 18 bytes at position 0x1aaf. The length is defined as the full string length in bytes, including the trailing null byte. Example:
``hello, world'' at address 0x123456
is transmitted as
123456/d
The buffer of type struct stat used by the target and gdb is defined as follows:
struct stat {
unsigned int st_dev; /* device */
unsigned int st_ino; /* inode */
mode_t st_mode; /* protection */
unsigned int st_nlink; /* number of hard links */
unsigned int st_uid; /* user ID of owner */
unsigned int st_gid; /* group ID of owner */
unsigned int st_rdev; /* device type (if inode device) */
unsigned long st_size; /* total size, in bytes */
unsigned long st_blksize; /* blocksize for filesystem I/O */
unsigned long st_blocks; /* number of blocks allocated */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last change */
};
The integral datatypes are conforming to the definitions given in the approriate section (see Integral datatypes, for details) so this structure is of size 64 bytes.
The values of several fields have a restricted meaning and/or range of values.
st_dev: 0 file
1 console
st_ino: No valid meaning for the target. Transmitted unchanged.
st_mode: Valid mode bits are described in Appendix C. Any other
bits have currently no meaning for the target.
st_uid: No valid meaning for the target. Transmitted unchanged.
st_gid: No valid meaning for the target. Transmitted unchanged.
st_rdev: No valid meaning for the target. Transmitted unchanged.
st_atime, st_mtime, st_ctime:
These values have a host and file system dependent
accuracy. Especially on Windows hosts the file systems
don't support exact timing values.
The target gets a struct stat of the above representation and is responsible to coerce it to the target representation before continuing.
Note that due to size differences between the host and target representation of stat members, these members could eventually get truncated on the target.
The buffer of type struct timeval used by the target and gdb is defined as follows:
struct timeval {
time_t tv_sec; /* second */
long tv_usec; /* microsecond */
};
The integral datatypes are conforming to the definitions given in the approriate section (see Integral datatypes, for details) so this structure is of size 8 bytes.
The following values are used for the constants inside of the protocol. gdb and target are resposible to translate these values before and after the call as needed.
All values are given in hexadecimal representation.
O_RDONLY 0x0
O_WRONLY 0x1
O_RDWR 0x2
O_APPEND 0x8
O_CREAT 0x200
O_TRUNC 0x400
O_EXCL 0x800
All values are given in octal representation.
S_IFREG 0100000
S_IFDIR 040000
S_IRUSR 0400
S_IWUSR 0200
S_IXUSR 0100
S_IRGRP 040
S_IWGRP 020
S_IXGRP 010
S_IROTH 04
S_IWOTH 02
S_IXOTH 01
All values are given in decimal representation.
EPERM 1
ENOENT 2
EINTR 4
EBADF 9
EACCES 13
EFAULT 14
EBUSY 16
EEXIST 17
ENODEV 19
ENOTDIR 20
EISDIR 21
EINVAL 22
ENFILE 23
EMFILE 24
EFBIG 27
ENOSPC 28
ESPIPE 29
EROFS 30
ENAMETOOLONG 91
EUNKNOWN 9999
EUNKNOWN is used as a fallback error value if a host system returns any error value not in the list of supported error numbers.
SEEK_SET 0
SEEK_CUR 1
SEEK_END 2
All values are given in decimal representation.
INT_MIN -2147483648
INT_MAX 2147483647
UINT_MAX 4294967295
LONG_MIN -9223372036854775808
LONG_MAX 9223372036854775807
ULONG_MAX 18446744073709551615
Example sequence of a write call, file descriptor 3, buffer is at target address 0x1234, 6 bytes should be written:
<-Fwrite,3,1234,6request memory read from target ->m1234,6<- XXXXXX return "6 bytes written" ->F6
Example sequence of a read call, file descriptor 3, buffer is at target address 0x1234, 6 bytes should be read:
<-Fread,3,1234,6request memory write to target ->X1234,6:XXXXXXreturn "6 bytes read" ->F6
Example sequence of a read call, call fails on the host due to invalid file descriptor (EBADF):
<-Fread,3,1234,6->F-1,9
Example sequence of a read call, user presses Ctrl-C before syscall on host is called:
<-Fread,3,1234,6->F-1,4,C<-T02
Example sequence of a read call, user presses Ctrl-C after syscall on host is called:
<-Fread,3,1234,6->X1234,6:XXXXXX<-T02
In some applications, it is not feasable for the debugger to interrupt the program's execution long enough for the developer to learn anything helpful about its behavior. If the program's correctness depends on its real-time behavior, delays introduced by a debugger might cause the program to fail, even when the code itself is correct. It is useful to be able to observe the program's behavior without interrupting it.
Using GDB's trace and collect commands, the user can
specify locations in the program, and arbitrary expressions to evaluate
when those locations are reached. Later, using the tfind
command, she can examine the values those expressions had when the
program hit the trace points. The expressions may also denote objects
in memory — structures or arrays, for example — whose values GDB
should record; while visiting a particular tracepoint, the user may
inspect those objects as if they were in memory at that moment.
However, because GDB records these values without interacting with the
user, it can do so quickly and unobtrusively, hopefully not disturbing
the program's behavior.
When GDB is debugging a remote target, the GDB agent code running on the target computes the values of the expressions itself. To avoid having a full symbolic expression evaluator on the agent, GDB translates expressions in the source language into a simpler bytecode language, and then sends the bytecode to the agent; the agent then executes the bytecode, and records the values for GDB to retrieve later.
The bytecode language is simple; there are forty-odd opcodes, the bulk of which are the usual vocabulary of C operands (addition, subtraction, shifts, and so on) and various sizes of literals and memory reference operations. The bytecode interpreter operates strictly on machine-level values — various sizes of integers and floating point numbers — and requires no information about types or symbols; thus, the interpreter's internal data structures are simple, and each bytecode requires only a few native machine instructions to implement it. The interpreter is small, and strict limits on the memory and time required to evaluate an expression are easy to determine, making it suitable for use by the debugging agent in real-time applications.
The agent represents bytecode expressions as an array of bytes. Each
instruction is one byte long (thus the term bytecode). Some
instructions are followed by operand bytes; for example, the goto
instruction is followed by a destination for the jump.
The bytecode interpreter is a stack-based machine; most instructions pop their operands off the stack, perform some operation, and push the result back on the stack for the next instruction to consume. Each element of the stack may contain either a integer or a floating point value; these values are as many bits wide as the largest integer that can be directly manipulated in the source language. Stack elements carry no record of their type; bytecode could push a value as an integer, then pop it as a floating point value. However, GDB will not generate code which does this. In C, one might define the type of a stack element as follows:
union agent_val {
LONGEST l;
DOUBLEST d;
};
where LONGEST and DOUBLEST are typedef names for
the largest integer and floating point types on the machine.
By the time the bytecode interpreter reaches the end of the expression,
the value of the expression should be the only value left on the stack.
For tracing applications, trace bytecodes in the expression will
have recorded the necessary data, and the value on the stack may be
discarded. For other applications, like conditional breakpoints, the
value may be useful.
Separate from the stack, the interpreter has two registers:
pcstartgoto and if_goto instructions.
There are no instructions to perform side effects on the running program, or call the program's functions; we assume that these expressions are only used for unobtrusive debugging, not for patching the running code.
Most bytecode instructions do not distinguish between the various sizes of values, and operate on full-width values; the upper bits of the values are simply ignored, since they do not usually make a difference to the value computed. The exceptions to this rule are:
refn)ext instruction
exists for this purpose.
ext n)If the interpreter is unable to evaluate an expression completely for some reason (a memory location is inaccessible, or a divisor is zero, for example), we say that interpretation “terminates with an error”. This means that the problem is reported back to the interpreter's caller in some helpful way. In general, code using agent expressions should assume that they may attempt to divide by zero, fetch arbitrary memory locations, and misbehave in other ways.
Even complicated C expressions compile to a few bytecode instructions;
for example, the expression x + y * z would typically produce
code like the following, assuming that x and y live in
registers, and z is a global variable holding a 32-bit
int:
reg 1
reg 2
const32 address of z
ref32
ext 32
mul
add
end
In detail, these mean:
reg 1x) onto the
stack.
reg 2y).
const32 address of zz onto the stack.
ref32z with z's value.
ext 32z is a signed integer.
muly * z.
addx + y * z.
endEach bytecode description has the following form:
add (0x02): a b => a+bIn this example, add is the name of the bytecode, and
(0x02) is the one-byte value used to encode the bytecode, in
hexidecimal. The phrase “a b => a+b” shows
the stack before and after the bytecode executes. Beforehand, the stack
must contain at least two values, a and b; since the top of
the stack is to the right, b is on the top of the stack, and
a is underneath it. After execution, the bytecode will have
popped a and b from the stack, and replaced them with a
single value, a+b. There may be other values on the stack below
those shown, but the bytecode affects only those shown.
Here is another example:
const8 (0x22) n: => nIn this example, the bytecode const8 takes an operand n
directly from the bytecode stream; the operand follows the const8
bytecode itself. We write any such operands immediately after the name
of the bytecode, before the colon, and describe the exact encoding of
the operand in the bytecode stream in the body of the bytecode
description.
For the const8 bytecode, there are no stack items given before
the =>; this simply means that the bytecode consumes no values
from the stack. If a bytecode consumes no values, or produces no
values, the list on either side of the => may be empty.
If a value is written as a, b, or n, then the bytecode treats it as an integer. If a value is written is addr, then the bytecode treats it as an address.
We do not fully describe the floating point operations here; although this design can be extended in a clean way to handle floating point values, they are not of immediate interest to the customer, so we avoid describing them, to save time.
float (0x01): =>add (0x02): a b => a+bsub (0x03): a b => a-bmul (0x04): a b => a*bdiv_signed (0x05): a b => a/bdiv_unsigned (0x06): a b => a/brem_signed (0x07): a b => a modulo brem_unsigned (0x08): a b => a modulo blsh (0x09): a b => a<<brsh_signed (0x0a): a b => (signed)a>>brsh_unsigned (0x0b): a b => a>>blog_not (0x0e): a => !abit_and (0x0f): a b => a&band.
bit_or (0x10): a b => a|bor.
bit_xor (0x11): a b => a^bor.
bit_not (0x12): a => ~aequal (0x13): a b => a=bless_signed (0x14): a b => a<bless_unsigned (0x15): a b => a<bext (0x16) n: a => a, sign-extended from n bitsThe number of source bits to preserve, n, is encoded as a single
byte unsigned integer following the ext bytecode.
zero_ext (0x2a) n: a => a, zero-extended from n bitsThe number of source bits to preserve, n, is encoded as a single
byte unsigned integer following the zero_ext bytecode.
ref8 (0x17): addr => aref16 (0x18): addr => aref32 (0x19): addr => aref64 (0x1a): addr => arefn, fetch an n-bit value from addr, using the
natural target endianness. Push the fetched value as an unsigned
integer.
Note that addr may not be aligned in any particular way; the
refn bytecodes should operate correctly for any address.
If attempting to access memory at addr would cause a processor
exception of some sort, terminate with an error.
ref_float (0x1b): addr => dref_double (0x1c): addr => dref_long_double (0x1d): addr => dl_to_d (0x1e): a => dd_to_l (0x1f): d => adup (0x28): a => a aswap (0x2b): a b => b apop (0x29): a =>if_goto (0x20) offset: a =>pc register to start + offset.
Thus, an offset of zero denotes the beginning of the expression.
The offset is stored as a sixteen-bit unsigned value, stored
immediately following the if_goto bytecode. It is always stored
most significant byte first, regardless of the target's normal
endianness. The offset is not guaranteed to fall at any particular
alignment within the bytecode stream; thus, on machines where fetching a
16-bit on an unaligned address raises an exception, you should fetch the
offset one byte at a time.
goto (0x21) offset: =>pc register to start + offset.
The offset is stored in the same way as for the if_goto bytecode.
const8 (0x22) n: => nconst16 (0x23) n: => nconst32 (0x24) n: => nconst64 (0x25) n: => next bytecode.
The constant n is stored in the appropriate number of bytes
following the constb bytecode. The constant n is
always stored most significant byte first, regardless of the target's
normal endianness. The constant is not guaranteed to fall at any
particular alignment within the bytecode stream; thus, on machines where
fetching a 16-bit on an unaligned address raises an exception, you
should fetch n one byte at a time.
reg (0x26) n: => aThe register number n is encoded as a 16-bit unsigned integer
immediately following the reg bytecode. It is always stored most
significant byte first, regardless of the target's normal endianness.
The register number is not guaranteed to fall at any particular
alignment within the bytecode stream; thus, on machines where fetching a
16-bit on an unaligned address raises an exception, you should fetch the
register number one byte at a time.
trace (0x0c): addr size =>trace_quick (0x0d) size: addr => addrtrace opcode.
This bytecode is equivalent to the sequence dup const8 size
trace, but we provide it anyway to save space in bytecode strings.
trace16 (0x30) size: addr => addrtrace_quick16, for consistency.
end (0x27): =>Here is a sketch of a full non-stop debugging cycle, showing how agent expressions fit into the process.
Some targets don't support floating-point, and some would rather not
have to deal with long long operations. Also, different targets
will have different stack sizes, and different bytecode buffer lengths.
Thus, GDB needs a way to ask the target about itself. We haven't worked out the details yet, but in general, GDB should be able to send the target a packet asking it to describe itself. The reply should be a packet whose length is explicit, so we can add new information to the packet in future revisions of the agent, without confusing old versions of GDB, and it should contain a version number. It should contain at least the following information:
long long is supported
This section documents the API used by the GDB agent to collect data on Symmetrix systems.
Cygnus originally implemented these tracing features to help EMC Corporation debug their Symmetrix high-availability disk drives. The Symmetrix application code already includes substantial tracing facilities; the GDB agent for the Symmetrix system uses those facilities for its own data collection, via the API described here.
Search the trace frame frame for memory saved from address. If the memory is available, provide the address of the buffer holding it; otherwise, provide the address of the next saved area.
- If the memory at address was saved in frame, set
*buffer to point to the buffer in which that memory was saved, set*size to the number of bytes from address that are saved at*buffer, and returnOK_TARGET_RESPONSE. (Clearly, in this case, the function will always set*size to a value greater than zero.)- If frame does not record any memory at address, set
*size to the distance from address to the start of the saved region with the lowest address higher than address. If there is no memory saved from any higher address, set*size to zero. ReturnNOT_FOUND_TARGET_RESPONSE.These two possibilities allow the caller to either retrieve the data, or walk the address space to the next saved area.
This function allows the GDB agent to map the regions of memory saved in a particular frame, and retrieve their contents efficiently.
This function also provides a clean interface between the GDB agent and the Symmetrix tracing structures, making it easier to adapt the GDB agent to future versions of the Symmetrix system, and vice versa. This function searches all data saved in frame, whether the data is there at the request of a bytecode expression, or because it falls in one of the format's memory ranges, or because it was saved from the top of the stack. EMC can arbitrarily change and enhance the tracing mechanism, but as long as this function works properly, all collected memory is visible to GDB.
The function itself is straightforward to implement. A single pass over the trace frame's stack area, memory ranges, and expression blocks can yield the address of the buffer (if the requested address was saved), and also note the address of the next higher range of memory, to be returned when the search fails.
As an example, suppose the trace frame f has saved sixteen bytes
from address 0x8000 in a buffer at 0x1000, and thirty-two
bytes from address 0xc000 in a buffer at 0x1010. Here are
some sample calls, and the effect each would have:
adbg_find_memory_in_frame (f, (char*) 0x8000, &buffer, &size)buffer to 0x1000, set size to
sixteen, and return OK_TARGET_RESPONSE, since f saves
sixteen bytes from 0x8000 at 0x1000.
adbg_find_memory_in_frame (f, (char *) 0x8004, &buffer, &size)buffer to 0x1004, set size to
twelve, and return OK_TARGET_RESPONSE, since f saves the
twelve bytes from 0x8004 starting four bytes into the buffer at
0x1000. This shows that request addresses may fall in the middle
of saved areas; the function should return the address and size of the
remainder of the buffer.
adbg_find_memory_in_frame (f, (char *) 0x8100, &buffer, &size)size to 0x3f00 and return
NOT_FOUND_TARGET_RESPONSE, since there is no memory saved in
f from the address 0x8100, and the next memory available
is at 0x8100 + 0x3f00, or 0xc000. This shows that request
addresses may fall outside of all saved memory ranges; the function
should indicate the next saved area, if any.
adbg_find_memory_in_frame (f, (char *) 0x7000, &buffer, &size)size to 0x1000 and return
NOT_FOUND_TARGET_RESPONSE, since the next saved memory is at
0x7000 + 0x1000, or 0x8000.
adbg_find_memory_in_frame (f, (char *) 0xf000, &buffer, &size)size to zero, and return
NOT_FOUND_TARGET_RESPONSE. This shows how the function tells the
caller that no further memory ranges have been saved.
As another example, here is a function which will print out the
addresses of all memory saved in the trace frame frame on the
Symmetrix INLINES console:
void
print_frame_addresses (FRAME_DEF *frame)
{
char *addr;
char *buffer;
unsigned long size;
addr = 0;
for (;;)
{
/* Either find out how much memory we have here, or discover
where the next saved region is. */
if (adbg_find_memory_in_frame (frame, addr, &buffer, &size)
== OK_TARGET_RESPONSE)
printp ("saved %x to %x\n", addr, addr + size);
if (size == 0)
break;
addr += size;
}
}
Note that there is not necessarily any connection between the order in
which the data is saved in the trace frame, and the order in which
adbg_find_memory_in_frame will return those memory ranges. The
code above will always print the saved memory regions in order of
increasing address, while the underlying frame structure might store the
data in a random order.
[[This section should cover the rest of the Symmetrix functions the stub relies upon, too.]]
Some of the design decisions apparent above are arguable.
First, note that you don't need different bytecodes for different operand sizes. You can generate code without knowing how big the stack elements actually are on the target. If the target only supports 32-bit ints, and you don't send any 64-bit bytecodes, everything just works. The observation here is that the MIPS and the Alpha have only fixed-size registers, and you can still get C's semantics even though most instructions only operate on full-sized words. You just need to make sure everything is properly sign-extended at the right times. So there is no need for 32- and 64-bit variants of the bytecodes. Just implement everything using the largest size you support.
GDB should certainly check to see what sizes the target supports, so the
user can get an error earlier, rather than later. But this information
is not necessary for correctness.
> or <= operators?less_ opcodes with log_not, and swap the order
of the operands, yielding all four asymmetrical comparison operators.
For example, (x <= y) is ! (x > y), which is ! (y <
x).
log_not?ext?zero_ext?log_not is equivalent to const8 0 equal; it's used in half
the relational operators.
ext n is equivalent to const8 s-n lsh const8
s-n rsh_signed, where s is the size of the stack elements;
it follows refm and reg bytecodes when the value
should be signed. See the next bulleted item.
zero_ext n is equivalent to constm mask
log_and; it's used whenever we push the value of a register, because we
can't assume the upper bits of the register aren't garbage.
ref operators?ref operators, and we
need the ext bytecode anyway for accessing bitfields.
ref operators?ref operators again, and
const32 address ref32 is only one byte longer.
refn operators have to support unaligned fetches?In particular, structure bitfields may be several bytes long, but follow no alignment rules; members of packed structures are not necessarily aligned either.
In general, there are many cases where unaligned references occur in
correct C code, either at the programmer's explicit request, or at the
compiler's discretion. Thus, it is simpler to make the GDB agent
bytecodes work correctly in all circumstances than to make GDB guess in
each case whether the compiler did the usual thing.
goto ops PC-relative?goto ops?Suppose we have multiple branch ops with different offset sizes. As I generate code left-to-right, all my jumps are forward jumps (there are no loops in expressions), so I never know the target when I emit the jump opcode. Thus, I have to either always assume the largest offset size, or do jump relaxation on the code after I generate it, which seems like a big waste of time.
I can imagine a reasonable expression being longer than 256 bytes. I can't imagine one being longer than 64k. Thus, we need 16-bit offsets. This kind of reasoning is so bogus, but relaxation is pathetic.
The other approach would be to generate code right-to-left. Then I'd
always know my offset size. That might be fun.
reg bytecode take a 16-bit register number?trace and trace_quick?x->y->z, the agent must record the values of x and
x->y as well as the value of x->y->z.
trace bytecodes make the interpreter less general?trace bytecodes, they don't get in
its way.
trace_quick consume its arguments the way everything else does?trace_quick is a kludge to save space; it
only exists so we needn't write dup const8 SIZE trace
before every memory reference. Therefore, it's okay for it not to
consume its arguments; it's meant for a specific context in which we
know exactly what it should do with the stack. If we're going to have a
kludge, it should be an effective kludge.
trace16 exist?dup const16
size trace in those cases.
Whatever we decide to do with trace16, we should at least leave
opcode 0x30 reserved, to remain compatible with the customer who added
it.
Copyright © 1989, 1991 Free Software Foundation, Inc.
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Everyone is permitted to copy and distribute verbatim copies
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This program is free software; you can redistribute it and/or modify
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! packet: Packets# (a comment): Command Syntax# in Modula-2: GDB/M2$: Value History$$: Value History$_ and info breakpoints: Set Breaks$_ and info line: Machine Code$_, $__, and value history: Memory$_, convenience variable: Convenience Vars$__, convenience variable: Convenience Vars$_exitcode, convenience variable: Convenience Vars$bpnum, convenience variable: Set Breaks$cdir, convenience variable: Source Path$cwdr, convenience variable: Source Path$tpnum: Create and Delete Tracepoints$trace_file: Tracepoint Variables$trace_frame: Tracepoint Variables$trace_func: Tracepoint Variables$trace_line: Tracepoint Variables$tracepoint: Tracepoint Variables--annotate: Mode Options--args: Mode Options--async: Mode Options--batch: Mode Options--baud: Mode Options--cd: Mode Options--command: File Options--core: File Options--directory: File Options--epoch: Mode Options--exec: File Options--fullname: Mode Options--interpreter: Mode Options--mapped: File Options--noasync: Mode Options--nowindows: Mode Options--nx: Mode Options--pid: File Options--quiet: Mode Options--readnow: File Options--se: File Options--silent: Mode Options--statistics: Mode Options--symbols: File Options--tty: Mode Options--tui: Mode Options--version: Mode Options--windows: Mode Options--write: Mode Options-b: Mode Options-break-after: GDB/MI Breakpoint Table Commands-break-condition: GDB/MI Breakpoint Table Commands-break-delete: GDB/MI Breakpoint Table Commands-break-disable: GDB/MI Breakpoint Table Commands-break-enable: GDB/MI Breakpoint Table Commands-break-info: GDB/MI Breakpoint Table Commands-break-insert: GDB/MI Breakpoint Table Commands-break-list: GDB/MI Breakpoint Table Commands-break-watch: GDB/MI Breakpoint Table Commands-c: File Options-d: File Options-data-disassemble: GDB/MI Data Manipulation-data-evaluate-expression: GDB/MI Data Manipulation-data-list-changed-registers: GDB/MI Data Manipulation-data-list-register-names: GDB/MI Data Manipulation-data-list-register-values: GDB/MI Data Manipulation-data-read-memory: GDB/MI Data Manipulation-display-delete: GDB/MI Data Manipulation-display-disable: GDB/MI Data Manipulation-display-enable: GDB/MI Data Manipulation-display-insert: GDB/MI Data Manipulation-display-list: GDB/MI Data Manipulation-e: File Options-environment-cd: GDB/MI Data Manipulation-environment-directory: GDB/MI Data Manipulation-environment-path: GDB/MI Data Manipulation-environment-pwd: GDB/MI Data Manipulation-exec-abort: GDB/MI Program Control-exec-arguments: GDB/MI Program Control-exec-continue: GDB/MI Program Control-exec-finish: GDB/MI Program Control-exec-interrupt: GDB/MI Program Control-exec-next: GDB/MI Program Control-exec-next-instruction: GDB/MI Program Control-exec-return: GDB/MI Program Control-exec-run: GDB/MI Program Control-exec-show-arguments: GDB/MI Program Control-exec-step: GDB/MI Program Control-exec-step-instruction: GDB/MI Program Control-exec-until: GDB/MI Program Control-f: Mode Options-file-exec-and-symbols: GDB/MI Program Control-file-exec-file: GDB/MI Program Control-file-list-exec-sections: GDB/MI Program Control-file-list-exec-source-file: GDB/MI Program Control-file-list-exec-source-files: GDB/MI Program Control-file-list-shared-libraries: GDB/MI Program Control-file-list-symbol-files: GDB/MI Program Control-file-symbol-file: GDB/MI Program Control-gdb-exit: GDB/MI Miscellaneous Commands-gdb-set: GDB/MI Miscellaneous Commands-gdb-show: GDB/MI Miscellaneous Commands-gdb-version: GDB/MI Miscellaneous Commands-interpreter-exec: GDB/MI Miscellaneous Commands-m: File Options-n: Mode Options-nw: Mode Options-p: File Options-q: Mode Options-r: File Options-s: File Options-stack-info-depth: GDB/MI Stack Manipulation-stack-info-frame: GDB/MI Stack Manipulation-stack-list-arguments: GDB/MI Stack Manipulation-stack-list-frames: GDB/MI Stack Manipulation-stack-list-locals: GDB/MI Stack Manipulation-stack-select-frame: GDB/MI Stack Manipulation-symbol-info-address: GDB/MI Symbol Query-symbol-info-file: GDB/MI Symbol Query-symbol-info-function: GDB/MI Symbol Query-symbol-info-line: GDB/MI Symbol Query-symbol-info-symbol: GDB/MI Symbol Query-symbol-list-functions: GDB/MI Symbol Query-symbol-list-lines: GDB/MI Symbol Query-symbol-list-types: GDB/MI Symbol Query-symbol-list-variables: GDB/MI Symbol Query-symbol-locate: GDB/MI Symbol Query-symbol-type: GDB/MI Symbol Query-t: Mode Options-target-attach: GDB/MI Target Manipulation-target-compare-sections: GDB/MI Target Manipulation-target-detach: GDB/MI Target Manipulation-target-disconnect: GDB/MI Target Manipulation-target-download: GDB/MI Target Manipulation-target-exec-status: GDB/MI Target Manipulation-target-list-available-targets: GDB/MI Target Manipulation-target-list-current-targets: GDB/MI Target Manipulation-target-list-parameters: GDB/MI Target Manipulation-target-select: GDB/MI Target Manipulation-thread-info: GDB/MI Thread Commands-thread-list-all-threads: GDB/MI Thread Commands-thread-list-ids: GDB/MI Thread Commands-thread-select: GDB/MI Thread Commands-var-assign: GDB/MI Variable Objects-var-create: GDB/MI Variable Objects-var-delete: GDB/MI Variable Objects-var-evaluate-expression: GDB/MI Variable Objects-var-info-expression: GDB/MI Variable Objects-var-info-num-children: GDB/MI Variable Objects-var-info-type: GDB/MI Variable Objects-var-list-children: GDB/MI Variable Objects-var-set-format: GDB/MI Variable Objects-var-show-attributes: GDB/MI Variable Objects-var-show-format: GDB/MI Variable Objects-var-update: GDB/MI Variable Objects-w: Mode Options-x: File Options., Modula-2 scope operator: M2 Scope.gnu_debuglink sections: Separate Debug Files/proc: SVR4 Process Information? packet: Packets@, referencing memory as an array: Arrays^done: GDB/MI Result Records^error: GDB/MI Result Records^running: GDB/MI Result Records_NSPrintForDebugger, and printing Objective-C objects: The Print Command with Objective-CA packet: Packetsabort (C-g): Miscellaneous Commandsaccept-line (Newline or Return): Commands For Historyactions: Tracepoint Actionsadbg_find_memory_in_frame: Tracing on Symmetrixadd-shared-symbol-file: Filesadd-symbol-file: Filesadvance location: Continuing and Steppingappend: Dump/Restore Filesapropos: Helpawatch: Set Watchpointsb (break): Set Breaksb packet: PacketsB packet: Packetsbacktrace: Backtracebackward-char (C-b): Commands For Movingbackward-delete-char (Rubout): Commands For Textbackward-kill-line (C-x Rubout): Commands For Killingbackward-kill-word (M-<DEL>): Commands For Killingbackward-word (M-b): Commands For Movingbeginning-of-history (M-<): Commands For Historybeginning-of-line (C-a): Commands For Movingbell-style: Readline Init File Syntaxbreak: Set Breaksbreak ... thread threadno: Thread Stopsbreak, and Objective-C: Method Names in Commandsbreakpoint: Annotations for Runningbreakpoint subroutine, remote: Stub Contentsbreakpoints-invalid: Invalidationbt (backtrace): Backtracec (continue): Continuing and Steppingc (SingleKey TUI key): TUI Single Key ModeC packet: Packetsc packet: PacketsC-L: TUI KeysC-o (operate-and-get-next): Command SyntaxC-x 1: TUI KeysC-x 2: TUI KeysC-x A: TUI KeysC-x a: TUI KeysC-x C-a: TUI KeysC-x o: TUI KeysC-x s: TUI Keyscall: Callingcall-last-kbd-macro (C-x e): Keyboard Macroscapitalize-word (M-c): Commands For Textcatch: Set Catchpointscatch catch: Set Catchpointscatch exec: Set Catchpointscatch fork: Set Catchpointscatch load: Set Catchpointscatch throw: Set Catchpointscatch unload: Set Catchpointscatch vfork: Set Catchpointscd: Working Directorycdir: Source Pathcharacter-search (C-]): Miscellaneous Commandscharacter-search-backward (M-C-]): Miscellaneous Commandsclear: Delete Breaksclear, and Objective-C: Method Names in Commandsclear-screen (C-l): Commands For Movingcollect (tracepoints): Tracepoint Actionscommands: Promptingcommands: Break Commandscomment-begin: Readline Init File Syntaxcomplete: Helpcomplete (<TAB>): Commands For Completioncompletion-query-items: Readline Init File Syntaxcondition: Conditionscontinue: Continuing and Steppingconvert-meta: Readline Init File Syntaxcopy-backward-word (): Commands For Killingcopy-forward-word (): Commands For Killingcopy-region-as-kill (): Commands For Killingcore: Filescore-file: Filescwd: Source Pathd (delete): Delete Breaksd (SingleKey TUI key): TUI Single Key Moded packet: PacketsD packet: Packetsdefine: Definedelete: Delete Breaksdelete display: Auto Displaydelete mem: Memory Region Attributesdelete tracepoint: Create and Delete Tracepointsdelete-char (C-d): Commands For Textdelete-char-or-list (): Commands For Completiondelete-horizontal-space (): Commands For Killingdetach: Attachdetach (remote): Connectingdevice: Renesas Boardsdigit-argument (M-0, M-1, ... M--): Numeric Argumentsdir: Source Pathdirectory: Source Pathdis (disable): Disablingdisable: Disablingdisable breakpoints: Disablingdisable display: Auto Displaydisable mem: Memory Region Attributesdisable tracepoint: Enable and Disable Tracepointsdisable-completion: Readline Init File Syntaxdisassemble: Machine Codedisconnect: Connectingdisplay: Auto Displaydll-symbols: Cygwin Nativedo (down): Selectiondo-uppercase-version (M-a, M-b, M-x, ...): Miscellaneous Commandsdocument: DefineDown: TUI Keysdown: Selectiondown-silently: Selectiondowncase-word (M-l): Commands For Textdump: Dump/Restore Filesdump-functions (): Miscellaneous Commandsdump-macros (): Miscellaneous Commandsdump-variables (): Miscellaneous Commandse (edit): Editecho: Outputedit: Editediting-mode: Readline Init File Syntaxelse: Defineenable: Disablingenable breakpoints: Disablingenable display: Auto Displayenable mem: Memory Region Attributesenable tracepoint: Enable and Disable Tracepointsenable-keypad: Readline Init File Syntaxend: Break Commandsend-kbd-macro (C-x )): Keyboard Macrosend-of-history (M->): Commands For Historyend-of-line (C-e): Commands For Movingerror: Errorserror-begin: ErrorsexceptionHandler: Bootstrappingexchange-point-and-mark (C-x C-x): Miscellaneous Commandsexec-file: Filesexited: Annotations for Runningexpand-tilde: Readline Init File Syntaxf (frame): Selectionf (SingleKey TUI key): TUI Single Key ModeF packet: PacketsF reply packet: The F reply packetF request packet: The F request packetfg (resume foreground execution): Continuing and Steppingfile: Filesfinish: Continuing and Steppingflush_i_cache: Bootstrappingfocus: TUI Commandsforward-backward-delete-char (): Commands For Textforward-char (C-f): Commands For Movingforward-search: Searchforward-search-history (C-s): Commands For Historyforward-word (M-f): Commands For Movingframe, command: Framesframe, selecting: Selectionframes-invalid: Invalidationg packet: PacketsG packet: Packetsg++, gnu C++ compiler: CGDBHISTFILE: Historygdbserve.nlm: NetWaregdbserver: ServergetDebugChar: Bootstrappinggnu_debuglink_crc32: Separate Debug Filesh (help): HelpH packet: Packetshandle: Signalshandle_exception: Stub Contentshbreak: Set Breakshelp: Helphelp target: Target Commandshelp user-defined: Defineheuristic-fence-post (Alpha, MIPS): MIPShistory-preserve-point: Readline Init File Syntaxhistory-search-backward (): Commands For Historyhistory-search-forward (): Commands For Historyhook: Hookshook-: Hookshookpost: Hookshookpost-: Hookshorizontal-scroll-mode: Readline Init File Syntaxhtrace disable: OpenRISC 1000htrace enable: OpenRISC 1000htrace info: OpenRISC 1000htrace mode continuous: OpenRISC 1000htrace mode suspend: OpenRISC 1000htrace print: OpenRISC 1000htrace qualifier: OpenRISC 1000htrace record: OpenRISC 1000htrace rewind: OpenRISC 1000htrace stop: OpenRISC 1000htrace trigger: OpenRISC 1000hwatch: OpenRISC 1000i (info): Helpi packet: PacketsI packet: Packetsif: Defineignore: ConditionsINCLUDE_RDB: VxWorksinfo: Helpinfo address: Symbolsinfo all-registers: Registersinfo args: Frame Infoinfo auxv: Auxiliary Vectorinfo breakpoints: Set Breaksinfo catch: Frame Infoinfo cisco: KODinfo classes: Symbolsinfo display: Auto Displayinfo dll: Cygwin Nativeinfo dos: DJGPP Nativeinfo extensions: Showinfo f (info frame): Frame Infoinfo files: Filesinfo float: Floating Point Hardwareinfo frame: Frame Infoinfo frame, show the source language: Showinfo functions: Symbolsinfo line: Machine Codeinfo line, and Objective-C: Method Names in Commandsinfo locals: Frame Infoinfo macro: Macrosinfo mem: Memory Region Attributesinfo or1k spr: OpenRISC 1000info proc: SVR4 Process Informationinfo proc mappings: SVR4 Process Informationinfo program: Stoppinginfo registers: Registersinfo s (info stack): Backtraceinfo scope: Symbolsinfo selectors: Symbolsinfo set: Helpinfo share: Filesinfo sharedlibrary: Filesinfo signals: Signalsinfo source: Symbolsinfo source, show the source language: Showinfo sources: Symbolsinfo stack: Backtraceinfo symbol: Symbolsinfo target: Filesinfo terminal: Input/Outputinfo threads: Threadsinfo tracepoints: Listing Tracepointsinfo types: Symbolsinfo variables: Symbolsinfo vector: Vector Unitinfo w32: Cygwin Nativeinfo watchpoints: Set Watchpointsinfo win: TUI Commandsinput-meta: Readline Init File Syntaxinsert-comment (M-#): Miscellaneous Commandsinsert-completions (M-*): Commands For Completioninspect: Datainterpreter-exec: Interpretersisearch-terminators: Readline Init File Syntaxjump: Jumpingjump, and Objective-C: Method Names in Commandsk packet: Packetskeymap: Readline Init File Syntaxkill: Kill Processkill-line (C-k): Commands For Killingkill-region (): Commands For Killingkill-whole-line (): Commands For Killingkill-word (M-d): Commands For Killingl (list): Listlayout asm: TUI Commandslayout next: TUI Commandslayout prev: TUI Commandslayout regs: TUI Commandslayout split: TUI Commandslayout src: TUI CommandsLeft: TUI Keyslist: Listlist, and Objective-C: Method Names in Commandsload filename: Target Commandsm packet: PacketsM packet: Packetsmacro define: Macrosmacro expand: Macrosmacro expand-once: Macrosmacro undef: Macrosmaint info breakpoints: Maintenance Commandsmaint info psymtabs: Symbolsmaint info sections: Filesmaint info symtabs: Symbolsmaint internal-error: Maintenance Commandsmaint internal-warning: Maintenance Commandsmaint print cooked-registers: Maintenance Commandsmaint print dummy-frames: Maintenance Commandsmaint print psymbols: Symbolsmaint print raw-registers: Maintenance Commandsmaint print reggroups: Maintenance Commandsmaint print register-groups: Maintenance Commandsmaint print registers: Maintenance Commandsmaint print symbols: Symbolsmaint set profile: Maintenance Commandsmaint show profile: Maintenance Commandsmake: Shell Commandsmapped: Filesmark-modified-lines: Readline Init File Syntaxmark-symlinked-directories: Readline Init File Syntaxmatch-hidden-files: Readline Init File Syntaxmem: Memory Region Attributesmemset: Bootstrappingmenu-complete (): Commands For Completionmeta-flag: Readline Init File Syntaxremotedebug protocol: MIPS Embeddedn (next): Continuing and Steppingn (SingleKey TUI key): TUI Single Key ModeNew systag message: ThreadsNew systag message, on HP-UX: Threadsnext: Continuing and Steppingnext-history (C-n): Commands For Historynexti: Continuing and Steppingni (nexti): Continuing and Steppingnon-incremental-forward-search-history (M-n): Commands For Historynon-incremental-reverse-search-history (M-p): Commands For Historyor1ksim: OpenRISC 1000output: Outputoutput-meta: Readline Init File Syntaxoverlay auto: Overlay Commandsoverlay load-target: Overlay Commandsoverlay manual: Overlay Commandsoverlay map-overlay: Overlay Commandsoverlay off: Overlay Commandsoverlay unmap-overlay: Overlay Commandsoverload-choice: Promptingoverwrite-mode (): Commands For Textp packet: PacketsP packet: Packetspage-completions: Readline Init File Syntaxpasscount: Tracepoint Passcountspath: EnvironmentPgDn: TUI KeysPgUp: TUI Keyspo (print-object): The Print Command with Objective-Cpossible-completions (M-?): Commands For Completionpost-commands: Promptingpost-overload-choice: Promptingpost-prompt: Promptingpost-prompt-for-continue: Promptingpost-query: Promptingpre-commands: Promptingpre-overload-choice: Promptingpre-prompt: Promptingpre-prompt-for-continue: Promptingpre-query: Promptingprefix-meta (<ESC>): Miscellaneous Commandsprevious-history (C-p): Commands For Historyprint: Dataprint-object: The Print Command with Objective-Cprintf: Outputprompt: Promptingprompt-for-continue: Promptingptype: SymbolsputDebugChar: Bootstrappingpwd: Working Directoryq (quit): Quitting GDBq (SingleKey TUI key): TUI Single Key Modeq packet: PacketsQ packet: Packetsquery: Promptingquit: Errorsquit [expression]: Quitting GDBquoted-insert (C-q or C-v): Commands For Textr (run): Startingr (SingleKey TUI key): TUI Single Key ModeR packet: Packetsr packet: Packetsrbreak: Set Breaksre-read-init-file (C-x C-r): Miscellaneous Commandsreadnow: Filesredraw-current-line (): Commands For Movingrefresh: TUI Commandsremotedebug, MIPS protocol: MIPS Embeddedremotetimeout: Sparcletrestore: Dump/Restore FilesRET (repeat last command): Command Syntaxretransmit-timeout, MIPS protocol: MIPS Embeddedreturn: Returningreverse-search: Searchreverse-search-history (C-r): Commands For Historyrevert-line (M-r): Miscellaneous CommandsRight: TUI Keysrun: Startingrwatch: Set Watchpointss (SingleKey TUI key): TUI Single Key Modes (step): Continuing and Steppings packet: PacketsS packet: Packetssave-tracepoints: save-tracepointssearch: Searchsection: Filesselect-frame: Framesself-insert (a, b, A, 1, !, ...): Commands For Texttarget remote: Connectingset: Helpset args: Argumentsset auto-solib-add: Filesset auto-solib-limit: Filesset backtrace limit: Backtraceset backtrace past-main: Backtraceset breakpoint pending: Set Breaksset charset: Character Setsset check range: Range Checkingset check type: Type Checkingset check, range: Range Checkingset check, type: Type Checkingset coerce-float-to-double: ABIset complaints: Messages/Warningsset confirm: Messages/Warningsset cp-abi: ABIset debug arch: Debugging Outputset debug event: Debugging Outputset debug expression: Debugging Outputset debug frame: Debugging Outputset debug overload: Debugging Outputset debug remote: Debugging Outputset debug serial: Debugging Outputset debug target: Debugging Outputset debug varobj: Debugging Outputset debug-file-directory: Separate Debug Filesset debugevents: Cygwin Nativeset debugexceptions: Cygwin Nativeset debugexec: Cygwin Nativeset debugmemory: Cygwin Nativeset demangle-style: Print Settingsset disassembly-flavor: Machine Codeset editing: Editingset endian auto: Byte Orderset endian big: Byte Orderset endian little: Byte Orderset environment: Environmentset extension-language: Showset follow-fork-mode: Processesset gnutarget: Target Commandsset height: Screen Sizeset history expansion: Historyset history filename: Historyset history save: Historyset history size: Historyset host-charset: Character Setsset input-radix: Numbersset language: Manuallyset listsize: Listset logging: Logging outputset machine: Renesas Specialset max-user-call-depth: Defineset memory mod: H8/500set mipsfpu: MIPS Embeddedset new-console: Cygwin Nativeset new-group: Cygwin Nativeset opaque-type-resolution: Symbolsset os: KODset osabi: ABIset output-radix: Numbersset overload-resolution: Debugging C plus plusset print address: Print Settingsset print array: Print Settingsset print asm-demangle: Print Settingsset print demangle: Print Settingsset print elements: Print Settingsset print max-symbolic-offset: Print Settingsset print null-stop: Print Settingsset print object: Print Settingsset print pretty: Print Settingsset print sevenbit-strings: Print Settingsset print static-members: Print Settingsset print symbol-filename: Print Settingsset print union: Print Settingsset print vtbl: Print Settingsset processor args: MIPS Embeddedset prompt: Promptset remote hardware-breakpoint-limit: Remote configurationset remote hardware-watchpoint-limit: Remote configurationset remote system-call-allowed 0: The system callset remote system-call-allowed 1: The system callset remotedebug, MIPS protocol: MIPS Embeddedset retransmit-timeout: MIPS Embeddedset rstack_high_address: A29Kset shell: Cygwin Nativeset solib-absolute-prefix: Filesset solib-search-path: Filesset step-mode: Continuing and Steppingset symbol-reloading: Symbolsset target-charset: Character Setsset timeout: MIPS Embeddedset trust-readonly-sections: Filesset tui active-border-mode: TUI Configurationset tui border-kind: TUI Configurationset tui border-mode: TUI Configurationset variable: Assignmentset verbose: Messages/Warningsset width: Screen Sizeset write: Patchingset-mark (C-@): Miscellaneous Commandsset_debug_traps: Stub Contentsshare: Filessharedlibrary: Filesshell: Shell Commandsshow: Helpshow args: Argumentsshow auto-solib-add: Filesshow auto-solib-limit: Filesshow backtrace limit: Backtraceshow backtrace past-main: Backtraceshow breakpoint pending: Set Breaksshow charset: Character Setsshow check range: Range Checkingshow check type: Type Checkingshow complaints: Messages/Warningsshow confirm: Messages/Warningsshow convenience: Convenience Varsshow copying: Helpshow cp-abi: ABIshow debug arch: Debugging Outputshow debug event: Debugging Outputshow debug expression: Debugging Outputshow debug frame: Debugging Outputshow debug overload: Debugging Outputshow debug remote: Debugging Outputshow debug serial: Debugging Outputshow debug target: Debugging Outputshow debug varobj: Debugging Outputshow debug-file-directory: Separate Debug Filesshow demangle-style: Print Settingsshow directories: Source Pathshow editing: Editingshow environment: Environmentshow gnutarget: Target Commandsshow height: Screen Sizeshow history: Historyshow host-charset: Character Setsshow input-radix: Numbersshow language: Showshow listsize: Listshow logging: Logging outputshow machine: Renesas Specialshow max-user-call-depth: Defineshow mipsfpu: MIPS Embeddedshow new-console: Cygwin Nativeshow new-group: Cygwin Nativeshow opaque-type-resolution: Symbolsshow os: KODshow osabi: ABIshow output-radix: Numbersshow paths: Environmentshow print address: Print Settingsshow print array: Print Settingsshow print asm-demangle: Print Settingsshow print demangle: Print Settingsshow print elements: Print Settingsshow print max-symbolic-offset: Print Settingsshow print object: Print Settingsshow print pretty: Print Settingsshow print sevenbit-strings: Print Settingsshow print static-members: Print Settingsshow print symbol-filename: Print Settingsshow print union: Print Settingsshow print vtbl: Print Settingsshow processor: MIPS Embeddedshow prompt: Promptshow remote system-call-allowed: The system callshow remotedebug, MIPS protocol: MIPS Embeddedshow retransmit-timeout: MIPS Embeddedshow rstack_high_address: A29Kshow shell: Cygwin Nativeshow solib-absolute-prefix: Filesshow solib-search-path: Filesshow symbol-reloading: Symbolsshow target-charset: Character Setsshow timeout: MIPS Embeddedshow user: Defineshow values: Value Historyshow verbose: Messages/Warningsshow version: Helpshow warranty: Helpshow width: Screen Sizeshow write: Patchingshow-all-if-ambiguous: Readline Init File Syntaxshows: Historysi (stepi): Continuing and Steppingsignal: Annotations for Runningsignal: Signalingsignal-name: Annotations for Runningsignal-name-end: Annotations for Runningsignal-string: Annotations for Runningsignal-string-end: Annotations for Runningsignalled: Annotations for Runningsilent: Break Commandssim: Z8000source: Source Annotationssource: Command Filesspeed: Renesas Boardsspr: OpenRISC 1000st2000 cmd: ST2000start-kbd-macro (C-x (): Keyboard Macrosstarting: Annotations for Runningstep: Continuing and Steppingstepi: Continuing and Steppingstop, a pseudo-command: Hooksstopping: Annotations for Runningsymbol-file: Filessysinfo: DJGPP Nativet packet: PacketsT packet: PacketsT packet reply: Stop Reply Packetstarget: Targetstarget abug: M68Ktarget array: MIPS Embeddedtarget core: Target Commandstarget cpu32bug: M68Ktarget dbug: M68Ktarget ddb port: MIPS Embeddedtarget dink32: PowerPCtarget e7000, with H8/300: H8/300target e7000, with Renesas ICE: Renesas ICEtarget e7000, with Renesas SH: SHtarget est: M68Ktarget exec: Target Commandstarget hms, and serial protocol: Renesas Boardstarget hms, with H8/300: H8/300target hms, with Renesas SH: SHtarget jtag: OpenRISC 1000target lsi port: MIPS Embeddedtarget m32r: M32R/Dtarget m32rsdi: M32R/Dtarget mips port: MIPS Embeddedtarget nrom: Target Commandstarget op50n: PAtarget pmon port: MIPS Embeddedtarget ppcbug: PowerPCtarget ppcbug1: PowerPCtarget r3900: MIPS Embeddedtarget rdi: ARMtarget rdp: ARMtarget remote: Target Commandstarget rom68k: M68Ktarget rombug: M68Ktarget sds: PowerPCtarget sh3, with H8/300: H8/300target sh3, with SH: SHtarget sh3e, with H8/300: H8/300target sh3e, with SH: SHtarget sim: Target Commandstarget sim, with Z8000: Z8000target sparclite: Sparclitetarget vxworks: VxWorkstarget w89k: PAtbreak: Set Breakstarget remote: Connectingtdump: tdumptfind: tfindthbreak: Set Breaksthis, inside C++ member functions: C plus plus expressionsthread apply: Threadsthread threadno: Threadstimeout, MIPS protocol: MIPS Embeddedtrace: Create and Delete Tracepointstranspose-chars (C-t): Commands For Texttranspose-words (M-t): Commands For Texttstart: Starting and Stopping Trace Experimenttstatus: Starting and Stopping Trace Experimenttstop: Starting and Stopping Trace Experimenttty: Input/Outputtui reg: TUI Commandsu (SingleKey TUI key): TUI Single Key Modeu (until): Continuing and Steppingtarget remote: Connectingundisplay: Auto Displayundo (C-_ or C-x C-u): Miscellaneous Commandsuniversal-argument (): Numeric Argumentsunix-line-discard (C-u): Commands For Killingunix-word-rubout (C-w): Commands For Killingunset environment: Environmentuntil: Continuing and Steppingup: SelectionUp: TUI Keysup-silently: Selectionupcase-word (M-u): Commands For Textupdate: TUI Commandsv (SingleKey TUI key): TUI Single Key ModevCont packet: PacketsvCont? packet: Packetsvisible-stats: Readline Init File Syntaxvxworks-timeout: VxWorksw (SingleKey TUI key): TUI Single Key Modewatch: Set Watchpointswatchpoint: Annotations for Runningwhatis: Symbolswhere: Backtracewhile: Definewhile-stepping (tracepoints): Tracepoint Actionswinheight: TUI Commandsx (examine memory): MemoryX packet: Packetsx(examine), and info line: Machine Codeyank (C-y): Commands For Killingyank-last-arg (M-. or M-_): Commands For Historyyank-nth-arg (M-C-y): Commands For Historyyank-pop (M-y): Commands For Killingz packet: PacketsZ packets: Packetsz0 packet: PacketsZ0 packet: Packetsz1 packet: PacketsZ1 packet: Packetsz2 packet: PacketsZ2 packet: Packetsz3 packet: PacketsZ3 packet: PacketsZ4 packet: Packetsz4 packet: Packets[1] gdb built with djgpp tools for MS-DOS/MS-Windows supports this mode of operation, but the event loop is suspended when the debuggee runs.
[2]
The only restriction is that your editor (say ex), recognizes the
following command-line syntax:
ex +number file
The optional numeric value +number designates the active line in the file.
[3] `b' cannot be used because these format letters are also
used with the x command, where `b' stands for “byte”;
see Examining memory.
[4] This is a way of removing
one word from the stack, on machines where stacks grow downward in
memory (most machines, nowadays). This assumes that the innermost
stack frame is selected; setting $sp is not allowed when other
stack frames are selected. To pop entire frames off the stack,
regardless of machine architecture, use return;
see Returning from a function.
[5] If you choose a port number that
conflicts with another service, gdbserver prints an error message
and exits.
[6] The DJGPP port of gdb uses the name gdb.ini instead, due to the limitations of file names imposed by DOS filesystems.
[7] On
DOS/Windows systems, the home directory is the one pointed to by the
HOME environment variable.
[8] In gdb-6.1/gdb/refcard.ps of the version 6.1 release.