From:	deleveld AT my-deja DOT com
Newsgroups:	comp.os.msdos.djgpp
Subject:	question about stack frames
Date:	Thu, 30 Dec 1999 15:07:50 GMT
Organization:	Deja.com - Before you buy.
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

Hello Everyone,

I have a question about DJGPP and stack frames.

I am working on a recursive function that has to recursive
quite a few times and I'd like to be able to calculate how many
times the function can recurse without overflowing the stack.

My function is like this:

static void _draw_recursive(Window* const window,
                            const ExposeEvent* const rect)
{
   ExposeEvent *event;
   Window* ptr = window->higher;

   ... do some stuff with the arguments and local variables ...

}

Now I have already tried to reduce the amount and size of local
variables. i.e. I need an Expose event and I malloc and free a
pointer in the function instead of making it a local varaible.

What confuses me is when I look at the assembler output for
the function I see this:

__draw_recursive:
	subl $44,%esp
	pushl %ebp
	pushl %edi
	pushl %esi
	pushl %ebx
	movl 64(%esp),%eax

   ... some other stuff ...

It looks to me like there are $44 bytes reserved on the stack
when I am pretty sure that I need a lot less that that.  I
calculate that I need at most 4 pointers i.e. 16 bytes.

Can anyone explain this do me?  Any advice on making the stack
frame as small as possible?

Thanks you,

Doug Eleveld



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