1; calculate the factorial
 2; 3! = 3 * 2 * 1
 3
 4; x86 32 bit example
 5
 6.section .data
 7
 8.section .text
 9.globl _start
10.globl factorial
11
12_start:
13  pushl $4          ; push argument (factorial 4)
14  call factorial
15  addl $4, %esp     ; scrub parameter, always return SP to where it was before
16                    ; we called a function
17  movl %eax, %ebx   ; store in ebx as our return status
18
19  movl $1, %eax
20  int $0x80
21
22.type factorial, @function
23factorial:
24  pushl %ebp          ; push so we can restore ebp afterwards
25  movl %esp, %ebp     ; we dont want to modify the SP so we push it to ebp
26  movl 8(%ebp), %eax
27  cmpl $1, %eax
28  je end_factorial
29  decl %eax
30  pushl %eax          ; push it for our call to factorial
31  call factorial
32  movl 8(%ebp), %ebx  ; reload our parameter in %ebx
33  imull %ebx, %eax
34
35end_factorial:
36  movl %ebp, %esp ; restoring ebp and esp to where
37  popl %ebp       ; they were before the function started
38
39  ret

 1; calculate the factorial
 2; 3! = 3 * 2 * 1
 3
 4; x86_64 64bit example
 5
 6.section .data
 7
 8.section .text
 9.globl _start
10.globl factorial
11
12_start:
13  movl $5, %rdi
14  call factorial
15  mov %rax, %rdi
16  jmp exit
17
18.type factorial, @function
19factorial:
20  movl %rdi, %rax
21  cmpl $1, %rax
22  je end_factorial
23  decl %rax
24  movl %rax, %rdi
25  call factorial
26  movl %rax, %rbx
27  imull %rbx, %rax
28
29exit:
30  ret