HelloAssembley OS X from https://lord.io/blog/2014/assembly-on-osx/ with a small bug fix

hello_world.asm

%define SYSCALL_WRITE 0x2000004
 %define SYSCALL_EXIT  0x2000001

global start
start:
  mov rdi, 1
  ;mov rsi, str
  lea rsi, [rel str]
  mov rdx, strlen
  mov rax, SYSCALL_WRITE
  syscall

  mov rax, SYSCALL_EXIT
  mov rdi, 0
  syscall

section .data
str:
  db `Hello, assembly!\n` ; to use escape sequences, use backticks
strlen equ $ - str