NASM Coding: Basics - Program Examples

2. ; A program that adds two constants and exits by returning the addition result.
   
   section .text
       global _start
   
   _start:
       mov rax, 5    ; Put 5 in rax
       mov rbx, 3    ; Put 3 in rbx
       add rax, rbx  ; Compute: rax += rbx
   
       mov rdi, rax  ; Put rax (= 3 + 5) in rdi
       mov rax, 60   ; Put the 'exit' syscall code in rax
       syscall       ; Call _exit(rdi), which is _exit(8)