popAndPush.asm

; Example using push and pop that swaps two numbers
section	.data
section .bss
num1 resb 1 ; declare variable to hold an ascii  number
num2 resb 1 ; declare a variable to hold an ascii number
section	.text
global _start   ;must be declared for linker (ld)
	
_start:	
 		
call swap ; call swap
call quit ; call switch
  swap :
mov rax,  '2' ; put 2 in 64-bit register rax
mov rbx, '3' ; put 3 in 64-bit register rbx
push rax ; push content of rax on stack
push rbx ; push content of rbx on stack
pop rax ; get value from top of stack and put in rbx
pop rbx ; get new value from top of stack and put in rax 
mov [num1], rax ; put value in rax in num1
mov [num2],rbx ; put value in rbx in num2
call display
ret


display:
; display the values
   mov  edx,1      ;message length
   mov  ecx, num1   ;message to write
   mov  ebx, 1     ;file descriptor (stdout)
   mov  eax, 4     ;system call number (sys_write)
   int  0x80       ;call kernel
	   mov  edx,1      ;message length
   mov  ecx, num2   ;message to write
   mov  ebx, 1     ;file descriptor (stdout)
   mov  eax, 4     ;system call number (sys_write)
   int  0x80       ;call kernel
   ret
quit:
; quit
   mov  eax, 1     ;system call number (sys_exit)
   int  0x80       ;call kernel