section .data ; Data segment
msg db "Hello, world!", 0x0a ; The string and newline char
section .text ; Text segment
global _start ; Default entry point for ELF linking
_start:
; SYSCALL: write(1, msg, 14)
mov eax, 4 ; Put 4 into eax, since write is syscall #4.
mov ebx, 1 ; Put 1 into ebx, since stdout is 1.
mov ecx, msg ; Put the address of the string into ecx.
mov edx, 14 ; Put 14 into edx, since our string is 14 bytes.
int 0x80 ; Call the kernel to make the system call happen.
; SYSCALL: exit(0)
mov eax, 1 ; Put 1 into eax, since exit is syscall #1.
mov ebx, 0 ; Exit with success.
int 0x80 ; Do the syscall.

usr@myhost:~# nasm -f elf32 helloworld32.asm
usr@myhost:~# ld -m elf_i386 helloworld32.o
usr@myhost:~# ./a.out
Hello, world!