test_input.in

;
; This program runs in 32-bit protected mode.
;  build: nasm -f elf -F stabs name.asm
;  link:  ld -o name name.o
;
; In 64-bit long mode you can use 64-bit registers
; e.g. rax instead of eax, rbx instead of ebx, etc.
; Also change "-f elf " for "-f elf64" in build command.
;
section .data; section for initialized data
str: db 'Hello world!', 0Ah; message string with new-line char
             ; at the end (10 decimal)
str_len: equ $ - str    ; calcs length of string (bytes) by
         ; subtracting this address ($ symbol)
    ; from the str's start address
section .text    ; this is the code section
global _start    ; _start is the entry point and needs global
         ; scope to be 'seen' by the linker --
     ; equivalent to main() in C/C++
_start:    ; definition of _start procedure begins here
    mov eax, 4    ; specify the sys_write function code
                ; (from OS vector table)
    mov ebx, 1    ; specify file descriptor stdout -- in gnu/linux,
                  ; everything's treated as a file, even hardware
                  ; devices
    mov ecx, str    ; move start _address_ of string message to ecx
                    ; register
    mov edx, str_len    ; move length of message (in bytes)
    int 80h    ; interrupt kernel to perform the system call we
               ; just set up - in gnu/linux services are
               ; requested through the kernel
    mov eax, 1    ; specify sys_exit function code
                  ; (from OS vector table)
    mov ebx, 0    ; specify return code for OS
                  ; (zero tells OS everything went fine)
    int 80h    ; interrupt kernel to perform system call
               ; (to exit)