helloWorld.asm

; ----------------------------------------------------------------------------------------
;Source: http://cs.lmu.edu/~ray/notes/x86assembly/ 
;Writes "Hello, World" to the console using only system calls. Runs on 64-bit Linux only.
; To assemble and run:
;
;     nasm -felf64 hello.asm && ld hello.o && ./a.out
; ----------------------------------------------------------------------------------------

        global  _start

        section .text
_start:
        ; write(1, message, 13)
        mov     rax, 1                  ; system call 1 is write
        mov     rdi, 1                  ; file handle 1 is stdout
        mov     rsi, message            ; address of string to output
        mov     rdx, 13                 ; number of bytes
        syscall                         ; invoke operating system to do the write

        ; exit(0)
        mov     eax, 60                 ; system call 60 is exit
        xor     rdi, rdi                ; exit code 0
        syscall                         ; invoke operating system to exit
message:
        db      "Hello, World", 10      ; note the newline at the end