Question

In x86 Assembly Language:

Develop a program that uses four signed, global, short variables A, B, C, D

Initialize each variable A, B, C, D to a different positive one-digit value

Somehow print the four values in order A B C D, space separated

Print a newline character

Reorder the values in the variables from the order A, B, C, D to B, C, D, A

• A -> B
• B -> C
• C -> D
• D -> A

Somehow print the four values in order A B C D, space separated

Answer 1

;How to run:
;> nasm -felf32 <filename>.asm
;> gcc -m32 <filename>.o
;> ./a.out

section .data
   ;declare four signed global variables A, B, C, D
   ;and initialize them with values 4, 7, 1, 5 respectively
   A dw 4
   B dw 7
   C dw 1
   D dw 5
   ;%d format for printf function for printing variables
   var_format db " %d ",0
   ;newline character(10) for printing newline
   newline_format db 10,0
  
section .text
   global main
   extern printf

main:
   ;print A, B, C, D values
   call print_ABCD
   ;print newline character
   call print_newline
   ;copy values of A, B, C, D to registers ax, bx, cx, dx respectively
   mov ax, word[A]
   mov bx, word[B]
   mov cx, word[C]
   mov dx, word[D]
   ;A -> B
   mov word[B], ax
   ;B -> C
   mov word[C], bx
   ;C -> D
   mov word[D], cx
   ;D -> A
   mov word[A], dx
   ;print all A, B, C, D values
   call print_ABCD
   ;print newline
   call print_newline
   ret

print_ABCD:
   ;save previous stack pointer
   push ebp
   mov ebp, esp
  
   ;print A
   pusha
   xor eax, eax
   mov ax, word[A]
   push eax
   push var_format
   call printf
   add esp, 8
   popa
  
   ;print B
   pusha
   xor eax, eax
   mov ax, word[B]
   push eax
   push var_format
   call printf
   add esp, 8
   popa

   ;print C
   pusha
   xor eax, eax
   mov ax, word[C]
   push eax
   push var_format
   call printf
   add esp, 8
   popa

   ;print D
   pusha
   xor eax, eax
   mov ax, word[D]
   push eax
   push var_format
   call printf
   add esp, 8
   popa

   mov esp, ebp
   pop ebp

   ret

print_newline:
   ;save previous stack pointer
   push ebp
   mov ebp, esp
  
   ;print newline character
   pusha
   push newline_format
   call printf
   add esp, 4
   popa

   mov esp, ebp
   pop ebp

   ret