Hello World on amd64 under Linux.

hello.S

# Hello World on amd64 under Linux.
#
# One way to build this is with: 
#
#    gcc hello.S  -s -nostartfiles -nostdlib -o hello
#
# for syscall numbers look in /usr/include/asm/unistd_64.h
# for examples look at http://99-bottles-of-beer.net/language-assembler-(amd64)-933.html
# for insipration look at http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html

hello:
	.string	"Hello world!\n"
	.globl	_start
_start:
        # write(1, hello, 13)
        mov     $1, %rdi
        mov     $hello, %rsi
        mov     $13, %rdx
        mov     $1, %rax 
        syscall

        # _exit(0)
        xor     %rdi, %rdi
        mov     $60, %rax
        syscall