What happens on the stack when calling a function? (gcc-3.4.3)

[Daniel Hepper]

> There was similar discusion maybe month ago.
I just found it, sorry that I didn't dig a little bit deeper.
> GCC just tries to align everything to 16 bytes boundary(this
> optimization is very "cheap" by the way), but if you need exact
> behavior then you should use -mpreferred-stack-boundary, more info
> you'll find:
> http://gcc.gnu.org/onlinedocs/gcc-3.4.3/gcc/i386-and-x86_002d64-Options.html
> (-mpreferred-stack-boundary)
Ok, I've read the thread and the chapter in the manpage. This explains
much, thanks alot for your help.
But I've further question that were not answered.

I'm still working with the example from my first post:
(gdb) list 1,14
1       #include <string.h>
2       void f( char *args) {
3               char buf1[10];
4               char buf2[4] = "ABC";
5               strcpy (buf1, args);
6       }
7
8       int main (int argc, char *argv[]) {
9               if (argc > 1) {
10                      printf("Input: %s\n", argv[1]);
11                      f(argv[1]);
12              }
13              return 0;
14      }
(gdb) break 6
Breakpoint 3 at 0x80483e4: file s1.c, line 6.
(gdb) run `python -c 'print "A"*9'`
Starting program: /mnt/data/studium/vi/rlp/bo/s1 `python -c 'print "A"*9'`
Input: AAAAAAAAA

Breakpoint 3, f (args=0xbffff3cc "AAAAAAAAA") at s1.c:6
6       }
(gdb) x/12x buf2
0xbffff174: 0x00434241      0x41414141      0x41414141      0x08040041
0xbffff184: 0xbffff198      0xbffff198      0x0804841a      0xbffff3cc
0xbffff194: 0xbffff3cc      0xb7fd617c      0xb7eb6fa8      0x00000002
(gdb) info frame 0
Stack frame at 0xbffff190:
 eip = 0x80483e4 in f (s1.c:6); saved eip 0x804841a
 called by frame at 0xbffff1a0
 source language c.
 Arglist at 0xbffff188, args: args=0xbffff3cc "AAAAAAAAA"
 Locals at 0xbffff188, Previous frame's sp is 0xbffff190
 Saved registers:
  ebp at 0xbffff188, eip at 0xbffff18c
(gdb)


It says saved ebp is at 0xbffff188. The value there is 0xbffff198. But
on the other hand, it says "called by frame at 0xbffff1a0". Shouldn't
this be the same value? And it seems like ebp is saved two times, at
0xbffff184 and at 0xbffff188? I would expect the saved eip at
0xbffff188, but it is at 0xbffff18c.
Can someone explain this behaviour, please?

Daniel Hepper