Hi all,
I tried compiling the above two programs :
on x86, 32 bit machines.
And when I used objdump on that I saw the following code.
Can anyone help me know,
Why in the objdump of our first program the esp is decremented by 18H
bytes
and in the second program the esp is decremented by 28H bytes.
How actually is teh memory allocated by gcc for local variables.
Kindly help.
int main()
{
char x;
return 0;
}
[root@localhost ~]# gcc test.c
[root@localhost ~]# objdump -S a.out | less
08048348 <main>:
8048348: 55 push %ebp
8048349: 89 e5 mov %esp,%ebp
804834b: 83 ec 18 sub $0x18,%esp
804834e: 83 e4 f0 and $0xfffffff0,%esp
8048351: b8 00 00 00 00 mov $0x0,%eax
8048356: 83 c0 0f add $0xf,%eax
8048359: 83 c0 0f add $0xf,%eax
804835c: c1 e8 04 shr $0x4,%eax
804835f: c1 e0 04 shl $0x4,%eax
8048362: 29 c4 sub %eax,%esp
8048364: b8 00 00 00 00 mov $0x0,%eax
8048369: c9 leave
804836a: c3 ret
804836b: 90 nop
int main()
{
double x,y,z;
char p,q,r;
return 0;
}
08048348 <main>:
8048348: 55 push %ebp
8048349: 89 e5 mov %esp,%ebp
804834b: 83 ec 28 sub $0x28,%esp
804834e: 83 e4 f0 and $0xfffffff0,%esp
8048351: b8 00 00 00 00 mov $0x0,%eax
8048356: 83 c0 0f add $0xf,%eax
8048359: 83 c0 0f add $0xf,%eax
804835c: c1 e8 04 shr $0x4,%eax
804835f: c1 e0 04 shl $0x4,%eax
8048362: 29 c4 sub %eax,%esp
8048364: b8 00 00 00 00 mov $0x0,%eax
8048369: c9 leave
804836a: c3 ret
804836b: 90 nop
--
Regards,
Sandeep
