Assembly program to turn 123 into 321 and print it.

reverse123.s

    .data
    
    Sf:    .string "%d\n"
    
    .text
    
    .globl  main
    main:
    
    
    # start main
      pushq   %rbp
      movq    %rsp, %rbp
      subq    $16, %rsp
      movq    %rbx, -8(%rbp)
      movq    %r12, -16(%rbp)
    
    
      movl  $123, %esi    # int n
      movl  $0, %edi    # int reverse
      movl $10, %ebx    # divisor
    
    
    L1:     # while n != 0
    
    cmpl $0, %esi
    je L2
    
    # reverse = reverse * 10
    imul $10, %edi
    
    # reverse = reverse + n % 10
    movl $0, %edx
    movl %edi, %eax
    idivl %ebx
    addl %edx, %edi
    
    # n = n / 10
    movl %esi, %eax
    movl $0, %edx
    idivl %ebx
    movl %eax, %esi
     
    jmp L1
    
    L2:  # end while
    
    movl %edi, %eax
    
    # print value
      movq   $Sf, %rdi               
      movl  %eax, %esi               
      movl    $0, %eax              
      call  printf                 
    
    # end main
      movq  $0, %rax               
      movq  -8(%rbp),  %rbx
      movq  -16(%rbp), %r12
      leave
      ret