hello world assembly x86

hello.asm

# Useful variables
STDIN equ 0
STDOUT equ 1
STDERR equ 2
SYS_READ equ 0
SYS_WRITE equ 4
SYS_EXIT equ 1
KERNEL equ 0x80

%macro syscall 0
    int	KERNEL        ;call kernel
%endmacro

%macro exit_success 0
    mov eax, SYS_EXIT
    syscall
%endmacro

section .data ; here we store variables
    msg db "Hello world!", 0xa ; 0xa is new line
    len equ $ - msg

section .text 
    global _start
    
_start: ; main function
    mov	edx,len     ;message length
    mov	ecx,msg     ;message to write
    mov	ebx,STDOUT       ;file descriptor (stdout)
    mov	eax,SYS_WRITE       ;system call number (sys_write)
    syscall
    exit_success