Hi,
This is (rather primitive) C code to execute a shell:
#include <stdio.h>
void main()
{
char *name[2];
name[0] = "/bin/sh";
name[1] = NULL;
execve(name[0], name, NULL);
}
It was compiled with
gcc -ggdb -o exec_shell exec_shell.c
What follows is the correspong gdb disassembly of function main:
(gdb) disassemble main
Dump of assembler code for function main:
0x080481f4 <main+0>: push %ebp
0x080481f5 <main+1>: mov %esp,%ebp
0x080481f7 <main+3>: sub $0x18,%esp
0x080481fa <main+6>: and $0xfffffff0,%esp
0x080481fd <main+9>: mov $0x0,%eax
0x08048202 <main+14>: sub %eax,%esp
0x08048204 <main+16>: movl $0x8095ce8,0xfffffff8(%ebp)
0x0804820b <main+23>: movl $0x0,0xfffffffc(%ebp)
0x08048212 <main+30>: movl $0x0,0x8(%esp,1)
0x0804821a <main+38>: lea 0xfffffff8(%ebp),%eax
0x0804821d <main+41>: mov %eax,0x4(%esp,1)
0x08048221 <main+45>: mov 0xfffffff8(%ebp),%eax
0x08048224 <main+48>: mov %eax,(%esp,1)
0x08048227 <main+51>: call 0x804ce40 <execve>
0x0804822c <main+56>: leave
0x0804822d <main+57>: ret
End of assembler dump.
Rest of the assembly code I more or less understand can somebody tell me
what purpose, if any, do the instructions
mov $0x0,%eax
sub %eax,%esp
serve ?
--
``A prince never lacks legitimate reasons to break his promise.''
-- Machiavelli
Date: Thu Sep 16 02:06:14 IST 2004
GNU/Linux [2.6.9-rc2] System: up 2:54
