Re: Modified Proposal for Context Sensitive Function Calls

Subject: Re: Modified Proposal for Context Sensitive Function Calls
From: Bassam Tabbara (bassam@novas.com)
Date: Wed Nov 20 2002 - 10:44:59 PST

Kevin to save time, and back and forth, can you perhaps prepare a presentation (by Tuesday's meeting when this issue is to be discussed) proposal that mimics John's and Joao's (preferrably same example stubs ...) so we won't have to wade through emails ?

-Bassam.

Kevin Cameron wrote:

 

"Stickley, John" wrote:

Kevin,

Kevin Cameron x3251 wrote: 

Your approach solves this problem, however I think a more elegant
way to solve it is, rather than to use dynamic binding as you suggest,
to have a globally scoped "C name" indication as part of the the
export declaration. This would be more consistent with the global
scoping used counterpart extern declarations for the SV-to-C
direction as was outlined by Andrezj today.











That still suffers from the inefficiency that you have one "C" name
for multiple (distinct) instances of the task/function, so you need
an extra level of indirection to get to the actual task or function.
Calculating the indirection may be nontrivial, so it is prefereable
to do it just once (as with the dynamic binding) rather than on 
every call.

I'll take efficiency over elegance :-)

The dynamic binding mechanisms are also less dependent on the linker's
capabilities, avoid C name clashes entirely, and also allow checking
that the arguments match up (which C linking doesn't). 

I'm OK with the "export  ... <module>::<function>" syntax (I used that
in the earlier e-mail proposal).

Kev.







I think either approach can be implemented equally
as efficiently.

If I were going to implement the C-to-SV capability I would have my

tool compiler generate a highly efficient, pre-compiled code wrapper
stubs

with the proper C names for each required (exported) function, along
with a

header file containing the function prototypes of the stubs that the
user could

include in his or her code.

Now by merely calling the stub function and passing the context

pointer your code will execute just as efficiently as calling the dynamically

bound function pointer to the stub function.

-- johnS





I'm afraid I have to disagree.
Since your scheme has a single C-to-SV



entry-point per module,
and mine can create an entry-point per instance



there is no way that your
scheme will be as fast - it always has to decode



the instance on each call.



To get the same/better efficiency
with your approach you would have to



add the instance name to
the export statement.



There is still no way to
check that arguments match if you just link by



C name.



Kev.




--

National Semiconductor, Tel: (408) 721 3251

2900 Semiconductor Drive, Mail Stop D3-500, Santa Clara, CA 95052-8090



-- 
Dr. Bassam Tabbara
Technical Manager, R&D

Novas Software, Inc.
bassam@novas.com
(408) 467-7893

 















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