From:	"Mark S. Novojilov" <novojilo AT explorer DOT uni-trier DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Asm Question
Date:	Fri, 19 Sep 1997 01:32:07 +0200
Organization:	Universitaet Trier
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To:	djgpp AT delorie DOT com
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Gurunandan R. Bhat wrote:

> Greetings,
>
> In what precise way does %ebp "characterise" a stack frame? Does it point
> to the first address on the current stack frame? If so shouldn't each
> nested procedure call redefine %ebp to set up a new stack frame for its
> use?
>
> I have looked at some .s files produced by gcc and all they do is push and
> pop %ebp at each procedure call. Where is it initialised if at all? I
> suspect that this is done in crt0.s but would be grateful for the range
> of line numbers in the relevant file where this is accomplished
>
> Many thanks in advance

  A standard entry to a function looks like:
pushl %ebp
movl %esp,%ebp <---- initializes ebp
...
at the end:
leave
ret

You allways get this picture if you compile
your programs with -standrad-stack-frame option, or something
like that. With this option all locals are accessed through %ebp,
but that means you have one register less for other purposes.
Compiler also can use %esp for accessing locals(more sophisticated),
then %ebp is used as a general purpose register or for whatever
purposes, and the compiler just make sure to restore previous ebp
after function leaves.

                         - Mark

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