Hello world Assembly x64 (C library, Windows)

; Hello world program
; Language: x86-64 (AMD64) Assembly
; Library: C Standard Library 64-bit (Microsoft ABI)

global _start

extern puts
extern exit

section .text
    mov rcx, message
    sub rsp, 40
    call puts
    xor rcx, rcx
    call exit

section .data
    message db 'Hello world!', 0xA, 0