-mapcs-frame- Generate a stack frame that is compliant with the ARM Procedure Call
Standard for all functions, even if this is not strictly necessary for
correct execution of the code. Specifying -fomit-frame-pointer
with this option will cause the stack frames not to be generated for
leaf functions. The default is -mno-apcs-frame.
-mapcs- This is a synonym for -mapcs-frame.
-mapcs-26- Generate code for a processor running with a 26-bit program counter,
and conforming to the function calling standards for the APCS 26-bit
option.
This option is deprecated. Future releases of the GCC will only support
generating code that runs in apcs-32 mode.
-mapcs-32- Generate code for a processor running with a 32-bit program counter,
and conforming to the function calling standards for the APCS 32-bit
option.
This flag is deprecated. Future releases of GCC will make this flag
unconditional.
-mthumb-interwork- Generate code which supports calling between the ARM and Thumb
instruction sets. Without this option the two instruction sets cannot
be reliably used inside one program. The default is
-mno-thumb-interwork, since slightly larger code is generated
when -mthumb-interwork is specified.
-mno-sched-prolog- Prevent the reordering of instructions in the function prolog, or the
merging of those instruction with the instructions in the function's
body. This means that all functions will start with a recognizable set
of instructions (or in fact one of a choice from a small set of
different function prologues), and this information can be used to
locate the start if functions inside an executable piece of code. The
default is -msched-prolog.
-mhard-float- Generate output containing floating point instructions. This is the
default.
-msoft-float- Generate output containing library calls for floating point.
Warning: the requisite libraries are not available for all ARM
targets. Normally the facilities of the machine's usual C compiler are
used, but this cannot be done directly in cross-compilation. You must make
your own arrangements to provide suitable library functions for
cross-compilation.
-msoft-float changes the calling convention in the output file;
therefore, it is only useful if you compile all of a program with
this option. In particular, you need to compile libgcc.a, the
library that comes with GCC, with -msoft-float in order for
this to work.
-mlittle-endian- Generate code for a processor running in little-endian mode. This is
the default for all standard configurations.
-mbig-endian- Generate code for a processor running in big-endian mode; the default is
to compile code for a little-endian processor.
-mwords-little-endian- This option only applies when generating code for big-endian processors.
Generate code for a little-endian word order but a big-endian byte
order. That is, a byte order of the form `32107654'. Note: this
option should only be used if you require compatibility with code for
big-endian ARM processors generated by versions of the compiler prior to
2.8.
-malignment-traps- Generate code that will not trap if the MMU has alignment traps enabled.
On ARM architectures prior to ARMv4, there were no instructions to
access half-word objects stored in memory. However, when reading from
memory a feature of the ARM architecture allows a word load to be used,
even if the address is unaligned, and the processor core will rotate the
data as it is being loaded. This option tells the compiler that such
misaligned accesses will cause a MMU trap and that it should instead
synthesize the access as a series of byte accesses. The compiler can
still use word accesses to load half-word data if it knows that the
address is aligned to a word boundary.
This option has no effect when compiling for ARM architecture 4 or later,
since these processors have instructions to directly access half-word
objects in memory.
-mno-alignment-traps- Generate code that assumes that the MMU will not trap unaligned
accesses. This produces better code when the target instruction set
does not have half-word memory operations (i.e. implementations prior to
ARMv4).
Note that you cannot use this option to access unaligned word objects,
since the processor will only fetch one 32-bit aligned object from
memory.
The default setting is -malignment-traps, since this produces
code that will also run on processors implementing ARM architecture
version 6 or later.
This option is deprecated and will be removed in the next release of GCC.
-mcpu=name- This specifies the name of the target ARM processor. GCC uses this name
to determine what kind of instructions it can emit when generating
assembly code. Permissible names are: `arm2', `arm250',
`arm3', `arm6', `arm60', `arm600', `arm610',
`arm620', `arm7', `arm7m', `arm7d', `arm7dm',
`arm7di', `arm7dmi', `arm70', `arm700',
`arm700i', `arm710', `arm710c', `arm7100',
`arm7500', `arm7500fe', `arm7tdmi', `arm8',
`strongarm', `strongarm110', `strongarm1100',
`arm8', `arm810', `arm9', `arm9e', `arm920',
`arm920t', `arm926ejs', `arm940t', `arm9tdmi',
`arm10tdmi', `arm1020t', `arm1026ejs',
`arm1136js', `arm1136jfs' ,`xscale', `iwmmxt',
`ep9312'.
-mtune=name- This option is very similar to the -mcpu= option, except that
instead of specifying the actual target processor type, and hence
restricting which instructions can be used, it specifies that GCC should
tune the performance of the code as if the target were of the type
specified in this option, but still choosing the instructions that it
will generate based on the cpu specified by a -mcpu= option.
For some ARM implementations better performance can be obtained by using
this option.
-march=name- This specifies the name of the target ARM architecture. GCC uses this
name to determine what kind of instructions it can emit when generating
assembly code. This option can be used in conjunction with or instead
of the -mcpu= option. Permissible names are: `armv2',
`armv2a', `armv3', `armv3m', `armv4', `armv4t',
`armv5', `armv5t', `armv5te', `armv6j',
`iwmmxt', `ep9312'.
-mfpe=number-mfp=number- This specifies the version of the floating point emulation available on
the target. Permissible values are 2 and 3. -mfp= is a synonym
for -mfpe=, for compatibility with older versions of GCC.
-mstructure-size-boundary=n- The size of all structures and unions will be rounded up to a multiple
of the number of bits set by this option. Permissible values are 8 and
32. The default value varies for different toolchains. For the COFF
targeted toolchain the default value is 8. Specifying the larger number
can produce faster, more efficient code, but can also increase the size
of the program. The two values are potentially incompatible. Code
compiled with one value cannot necessarily expect to work with code or
libraries compiled with the other value, if they exchange information
using structures or unions.
-mabort-on-noreturn- Generate a call to the function
abort at the end of a
noreturn function. It will be executed if the function tries to
return.
-mlong-calls-mno-long-calls- Tells the compiler to perform function calls by first loading the
address of the function into a register and then performing a subroutine
call on this register. This switch is needed if the target function
will lie outside of the 64 megabyte addressing range of the offset based
version of subroutine call instruction.
Even if this switch is enabled, not all function calls will be turned
into long calls. The heuristic is that static functions, functions
which have the `short-call' attribute, functions that are inside
the scope of a `#pragma no_long_calls' directive and functions whose
definitions have already been compiled within the current compilation
unit, will not be turned into long calls. The exception to this rule is
that weak function definitions, functions with the `long-call'
attribute or the `section' attribute, and functions that are within
the scope of a `#pragma long_calls' directive, will always be
turned into long calls.
This feature is not enabled by default. Specifying
-mno-long-calls will restore the default behavior, as will
placing the function calls within the scope of a `#pragma
long_calls_off' directive. Note these switches have no effect on how
the compiler generates code to handle function calls via function
pointers.
-mnop-fun-dllimport- Disable support for the
dllimport attribute.
-msingle-pic-base- Treat the register used for PIC addressing as read-only, rather than
loading it in the prologue for each function. The run-time system is
responsible for initializing this register with an appropriate value
before execution begins.
-mpic-register=reg- Specify the register to be used for PIC addressing. The default is R10
unless stack-checking is enabled, when R9 is used.
-mcirrus-fix-invalid-insns- Insert NOPs into the instruction stream to in order to work around
problems with invalid Maverick instruction combinations. This option
is only valid if the -mcpu=ep9312 option has been used to
enable generation of instructions for the Cirrus Maverick floating
point co-processor. This option is not enabled by default, since the
problem is only present in older Maverick implementations. The default
can be re-enabled by use of the -mno-cirrus-fix-invalid-insns
switch.
-mpoke-function-name- Write the name of each function into the text section, directly
preceding the function prologue. The generated code is similar to this:
t0
.ascii "arm_poke_function_name", 0
.align
t1
.word 0xff000000 + (t1 - t0)
arm_poke_function_name
mov ip, sp
stmfd sp!, {fp, ip, lr, pc}
sub fp, ip, #4
When performing a stack backtrace, code can inspect the value of
pc stored at fp + 0. If the trace function then looks at
location pc - 12 and the top 8 bits are set, then we know that
there is a function name embedded immediately preceding this location
and has length ((pc[-3]) & 0xff000000).
-mthumb- Generate code for the 16-bit Thumb instruction set. The default is to
use the 32-bit ARM instruction set.
-mtpcs-frame- Generate a stack frame that is compliant with the Thumb Procedure Call
Standard for all non-leaf functions. (A leaf function is one that does
not call any other functions.) The default is -mno-tpcs-frame.
-mtpcs-leaf-frame- Generate a stack frame that is compliant with the Thumb Procedure Call
Standard for all leaf functions. (A leaf function is one that does
not call any other functions.) The default is -mno-apcs-leaf-frame.
-mcallee-super-interworking- Gives all externally visible functions in the file being compiled an ARM
instruction set header which switches to Thumb mode before executing the
rest of the function. This allows these functions to be called from
non-interworking code.
-mcaller-super-interworking- Allows calls via function pointers (including virtual functions) to
execute correctly regardless of whether the target code has been
compiled for interworking or not. There is a small overhead in the cost
of executing a function pointer if this option is enabled.