retroforth/experimental/linux.s

;  ___ ___ _____ ___  ___      __  _    _
; | _ \ __|_   _| _ \/ _ \    / / | |  (_)_ _ _  ___ __
; |   / _|  | | |   / (_) |  / /  | |__| | ' \ || \ \ /
; |_|_\___| |_| |_|_\\___/  /_/   |____|_|_||_\_,_/_\_\
;
; This is the minimal startup + I/O functionality needed to run
; RETRO on a Linux x86 system.
; =============================================================

bits 32

section .text
global putchar
global getchar
global _start
extern main

align 4

_start:
  call main
  jmp  $

align 4
putchar:
  mov eax, [esp+4]
  mov [buf], eax
  mov edx, 1
  mov ecx, buf
  mov ebx, 1
  mov eax, 4
  int 0x80
  ret

align 4
getchar:
  mov edx, 1
  mov ecx, buf
  mov ebx, 0
  mov eax, 3
  int 0x80
  mov eax, 0
  mov eax, [buf]
  ret

section .data
buf:
  dd 0
  dd 0
  dd 0
  dd 0