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From: Nicolas George on 28 Apr 2010 07:32
Noob wrote in message <hr95v3$52f$1(a)speranza.aioe.org>:
> .text
> .globl _get_current_stack_pointer
> _get_current_stack_pointer:
> movl %esp, %eax
> ret

void *get_approx_stack_pointer(void)
{
int a;
return(&a);
}
From: boltar2003 on 28 Apr 2010 07:46
On 28 Apr 2010 11:32:18 GMT
Nicolas George <nicolas$george(a)salle-s.org> wrote:
>Noob wrote in message <hr95v3$52f$1(a)speranza.aioe.org>:
>> .text
>> .globl _get_current_stack_pointer
>> _get_current_stack_pointer:
>> movl %esp, %eax
>> ret
>
>void *get_approx_stack_pointer(void)
>{
> int a;
> return(&a);
>}

Ah , very elegant and so obvious when you see it, but of course thinking
it up is always harder!

Of course it doesn't tell me when I'll hit the limit but its certainly
more useful than guessing.

Is there a way of knowing where stack bottom will be or this is an unfixed
quantity that simply varies depending on how much free memory the OS has?

Thanks

B2003

From: Noob on 28 Apr 2010 07:47
Nicolas George wrote:

> Noob wrote:
>
>> .text
>> .globl _get_current_stack_pointer
>> _get_current_stack_pointer:
>> movl %esp, %eax
>> ret
>
> void *get_approx_stack_pointer(void)
> {
> int a;
> return(&a);
> }

3.1.2.4 Storage durations of objects

The value of a pointer that referred to an object with automatic storage
duration that is no longer guaranteed to be reserved is indeterminate.

AFAIU, a conforming compiler is free to change the function to

void *get_approx_stack_pointer(void)
{
return NULL;
}

However, gcc 4.3.2 does not perform this optimization.

$ cat bar.c
void *get_approx_stack_pointer(void)
{
int a;
return(&a);
}

$ gcc -O3 -fomit-frame-pointer -Wall -S bar.c
bar.c: In function 'get_approx_stack_pointer':
bar.c:4: warning: function returns address of local variable

_get_approx_stack_pointer:
subl $16, %esp
leal 12(%esp), %eax
addl $16, %esp
ret

Regards.
From: Öö Tiib on 28 Apr 2010 07:53
On Apr 28, 1:01 pm, boltar2...(a)boltar.world wrote:

> This crashes too:
>
> $ cat t.c
> void func()
> {
>         func();
>
> }
>
> int main()
> {
>         func();}
>
> $ cc t.c
> $ a.out
> Segmentation fault (core dumped)

Yes. Like i said in other thread you have to do some undefined by
standard things that are usually defined by platform or implementation
documentation. Microsoft for example throws seh (microsoft term)
exceptions and for restoring the damaged stack there is some sort of:

int _resetstkoflw();

I do not use such techniques, instead i avoid deep recursion. To avoid
deep recursion i avoid deep trees.
From: Nicolas George on 28 Apr 2010 08:12
Noob wrote in message <hr977p$78u$1(a)speranza.aioe.org>:
> AFAIU, a conforming compiler is free to change the function to
>
> void *get_approx_stack_pointer(void)
> {
> return NULL;
> }

Of course, there is nothing portable in examining the stack pointer; the
very notion of stack is not portable. This is just a debugging trick.
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