hello.asm

hello.asm

;; ---- HELP ----

;; rax        [64x] CPU cache — temporary register. `syscal` uses this
;; rdi        [64x] CPU cache — 1st argument. 
;; rsi        [64x] CPU cache — 2nd argument.
;; rdx        [64x] CPU cache — 3rd argument.

;; syscall    [all] Call a system function. ID gotten from `rax`
;;            - See: https://github.com/torvalds/linux/blob/097f70b3c4d84ffccca15195bdfde3a37c0a7c0f/include/linux/syscalls.h
;;            *   1     sys_write: Output an array
;;            *  60     sys_exit: Exit

;; long sys_write(unsigned int fd, const char __user *buf, size_t count);
;; long sys_exit(int error_code);

;; Compile and run with
;; ```nasm -f elf64 -o hello.o hello.asm
;; ld -o hello hello.o
;; ./hello```


section .data                            ;; Variables here
    msg db      "Hello, world!", 10      ;; Hello world variable as `msg`
    len equ     $-msg                    ;; Length of `msg`

section .text                            ;; Code below here
    global _start                        ;; Define _start

_start:                                  ;; Initialize _start, then run
    mov       rax,  1
    mov       rdi,  1
    mov       rsi,  msg
    mov       rdx,  len
    syscall
    mov       rax,  60
    mov       rdi,  0
    syscall