Hello world in assembler

hello_x32.s

segment .text	   ;code segment
   global _start    ;must be declared for linker 
	
_start:	           ;tell linker entry point
   mov edx,len	   ;message length
   mov ecx,msg     ;message to write
   mov ebx,1	     ;file descriptor (stdout)
   mov eax,4	     ;system call number (sys_write)
   int 0x80	       ;call kernel

   mov eax,1       ;system call number (sys_exit)
   int 0x80	       ;call kernel

segment .data      ;data segment
msg	db 'Hello, world!',0xa   ;our dear string
len	equ	$ - msg    ;length of our dear string

hello_x64.s

section .data
    msg db "Hello world!", 0ah
    len equ $ - msg

section .text
    global _start

_start:
    mov rax, 1
    mov rdi, 1
    mov rsi, msg
    mov rdx, len
    syscall
    mov rax, 60
    mov rdi, 0
    syscall