Hello World (Assembly Intel x86 Linux)

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This is the traditional "Hello World!" program in NASM for Linux.

Data segment

We use the .data section to store the string and name it msg.

<<hello_world.asm>>=
section .data
msg	db	"Hello World!",0x0a

This code calculates the length of msg, and stores it in len.

<<hello_world.asm>>=
len	equ	$-msg

Text segment

The .text section contains the actual code. _start is the entry point.

<<hello_world.asm>>=
section .text
	global _start
_start:

We use the write system call to output the text string on standard output. This call takes 3 arguments: file descriptor, pointer to buffer, length of buffer. The registers ebx, ecx and edx are used to store these arguments. We store the system call number 4 for write in eax. System calls are invoked with int 0x80.

<<hello_world.asm>>=
	mov	ebx,0x01
	mov	ecx,msg
	mov	edx,len
	mov	eax,0x04
	int	0x80

When write is finished, we call exit, which has number 1, with argument 0. The exit call will never return.

<<hello_world.asm>>=
	mov	ebx,0x00
	mov	eax,0x01
	int	0x80

Run

This is how to compile and run this code:

nasm -f elf hello_world.asm
ld -s -o hello_world hello_world.o
./hello_world

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