Hello world Assembly x64 (Linux)

; Hello world program
; Language: x86-64 (AMD64) Assembly
; Library: Linux system calls

global _start

section .text
_start:
    mov rdx, message_length
    mov rsi, message
    mov rdi, 1
    mov rax, 1
    syscall
    xor rdi, rdi
    mov rax, 60
    syscall

section .data
    message db 'Hello world!', 0xA
    message_length equ $ - message