Hi,
0x08048352 <main+14>: sub $0x10,%esp
The above instruction allocates the memory on the stack... 16 bytes in
this case.
On 7/20/07, kanishk rastogi <kanishk.85@gmail.com> wrote:
On 7/20/07, Pankaj Kohli <pankaj208@gmail.com> wrote:
> Hi,
>
> I wrote a simple C program to test the memory allocation for local
> variables. But when i try to disassemble the program using gdb, it
> shows that 16 bytes are being reserved for local variables on the
> stack, although i declared a single integer variable which is supposed
> to take only 4 bytes.
> Can anyone tell, why it is reserving 16 bytes on the stack for just a
> single variable ? Is it some kind of optimization done by gcc ?
> Does the exact value depends on the operating system and/or gcc
version ?
>
> #include <stdio.h>
> int main(int argc, char **argv) {
> int x=10;
>
> return 0;
> }
>
> Breakpoint 1, main () at test7.c:4
> 4 int x=10;
> (gdb) disassemble main
> Dump of assembler code for function main:
> 0x08048344 <main+0>: lea 0x4(%esp),%ecx
> 0x08048348 <main+4>: and $0xfffffff0,%esp
> 0x0804834b <main+7>: pushl 0xfffffffc(%ecx)
> 0x0804834e <main+10>: push %ebp
> 0x0804834f <main+11>: mov %esp,%ebp
> 0x08048351 <main+13>: push %ecx
> 0x08048352 <main+14>: sub $0x10,%esp
> 0x08048355 <main+17>: movl $0xa,0xfffffff8(%ebp)
> 0x0804835c <main+24>: mov $0x0,%eax
> 0x08048361 <main+29>: add $0x10,%esp
> 0x08048364 <main+32>: pop %ecx
> 0x08048365 <main+33>: pop %ebp
> 0x08048366 <main+34>: lea 0xfffffffc(%ecx),%esp
> 0x08048369 <main+37>: ret
> End of assembler dump.
>
why do u say that its allocating 16 byte for integer
> --
> - Pankaj
>