Re: Smashing the Stack?

[Gigi Sullivan <sullivan () sikurezza org>]

Aiee :)

   Hello!

On Wed, Jul 17, 2002 at 08:46:58AM -0700, Jeremy Junginger wrote:
> void function(int a, int b, int c) {
>       char buffer1[5];
>       char buffer2[10];
>
> void main() {
>       function(1,2,3);
> }
>
> in "word" (4 byte) increments.   That makes sense; however, when I
> generate the assembly code with the exact same code, I see that it is
> subtracting 40 rather than the expected 20
> (bufger1(5bytes=2words=8bytes+10bytes=3words=12bytes).  This part looks

   This should be due to default stack boundary that gcc uses. Version 2.7.2.3
   (quite old) seems to have default stack boundary set to 2; that means
   that you have stuff on a 2^2=4 byte, i.e. dword boundary.

   For example, gcc 2.95.2 seems to set this default to 3, IIRC. 
   To change this, just compile using -mpreferred-stack-boundary=2 so you'll
   get the "usual" stuff on a dword (4 byte) boundary.

   Hope this helps.

bye bye

                           -- gg sullivan

-- 
Lorenzo Cavallaro `Gigi Sullivan' <sullivan () sikurezza org>

Until I loved, life had no beauty;
I did not know I lived until I had loved. (Theodor Korner)