section .data;
msg db "Hello world",0x0a;

section .text;
global_start;

_start:
    mov eax, 4;
    mov ebx, 1;
    mov ecx, msg;
    int 0x80;

    mov eax, 1;
    mov ebx, 0;
    int 0x80;
-----------------------
>> nasm -f elf code.asm
code.asm:5: warning: label alone on a line without a colon might be in error [-w+orphan-labels]