very easy hello world assembly code for x86 architecture

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 ; interrupt number

%macro syscall 0
    int	KERNEL        ;call kernel [interrupt]
%endmacro

%macro exit_success 0
    mov eax, SYS_EXIT 
    syscall
%endmacro


section .data
    msg db "Hello world!", 0x0a ; 0x0a in decimel is new line ascii
    len equ $ - msg ; $ indicates the 'current location' of the assembler 

section .text
    global _start

_start:
    mov ecx, msg
    mov edx, len
    mov ebx, STDOUT
    mov eax, SYS_WRITE
    syscall
    
    exit_success