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.
--
- Pankaj
