section .data
VAL_A dw 111
VAL_B dw 222
message db "The values were swapped.", 10
message_len equ $ - message
section .text
global _start
_start:
; Five valid MOV forms:
; 1. Immediate to register
; 2. Immediate to memory
; 3. Register to register
; 4. Register to memory
; 5. Memory to register
; Memory-to-memory MOV is invalid and must be avoided.
lea rbx, [rel VAL_A] ; RBX holds the address of VAL_A
lea rsi, [rel VAL_B] ; RSI holds the address of VAL_B
; Swap the word values using a temporary register.
mov ax, [rbx] ; Load VAL_A into AX
mov dx, [rsi] ; Load VAL_B into DX
mov [rbx], dx ; Store old VAL_B into VAL_A
mov [rsi], ax ; Store old VAL_A into VAL_B

; Display the confirmation message.
mov eax, 1 ; sys_write
mov edi, 1 ; standard output
lea rsi, [rel message]
mov edx, message_len
syscall
; Exit cleanly.
mov eax, 60 ; sys_exit
xor edi, edi ; exit status 0
syscall