kernel2/crt0.asm

   1 ;    meinOS - A unix-like x86 microkernel operating system
   2 ;    Copyright (C) 2008  Janosch Gräf <janosch.graef@gmx.net>
   3 ;
   4 ;    This program is free software: you can redistribute it and/or modify
   5 ;    it under the terms of the GNU General Public License as published by
   6 ;    the Free Software Foundation, either version 3 of the License, or
   7 ;    (at your option) any later version.
   8 ;
   9 ;    This program is distributed in the hope that it will be useful,
  10 ;    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 ;    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 ;    GNU General Public License for more details.
  13 ;
  14 ;    You should have received a copy of the GNU General Public License
  15 ;    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  16
  17 global _start
  18 global init_stack
  19 global init_stacksize
  20 extern main
  21
  22 ; setting up the Multiboot header - see GRUB docs for details
  23 ; Flags:
  24 ;  ModuleAlign: false
  25 ;  MemoryMap:   true
  26 ;  VideoMode:   true
  27 ;
  28 MST_FLAGS    equ  0000000000000000b
  29 OPT_FLAGS    equ  0000000000000110b
  30 FLAGS        equ  (MST_FLAGS<<16)|OPT_FLAGS
  31 MAGIC        equ    0x1BADB002           ; 'magic number' lets bootloader find the header
  32 CHECKSUM     equ -(MAGIC + FLAGS)        ; checksum required
  33 ; Video Info
  34 VIDEOMODE    equ 0   ; Textmode
  35 VIDEOWIDTH   equ 80  ; 80 Cols
  36 VIDEOHEIGHT  equ 25  ; 25 Lines
  37 VIDEODEPTH   equ 0   ; Depth
  38 ; reserve initial kernel stack space
  39 STACKSIZE    equ 4*1024
  40
  41 section .text
  42 align 4
  43
  44 MultiBootHeader:
  45         dd MAGIC       ; Magic number
  46         dd FLAGS       ; Flags
  47         dd CHECKSUM    ; Checksum
  48         times 5 dd 0   ; unused fields
  49         dd VIDEOMODE   ; Videomode
  50         dd VIDEOWIDTH  ; Videowidth
  51         dd VIDEOHEIGHT ; Videoheight
  52         dd VIDEODEPTH  ; Videodepth
  53
  54 _start:
  55         mov esp, init_stack+STACKSIZE-4 ; set up the stack
  56
  57         push eax ; pass Multiboot magic number
  58         push ebx ; pass Multiboot info structure
  59         call main ; call kernel function
  60         add esp,8
  61
  62         cli ; halt machine should kernel return
  63         hlt
  64
  65 init_stacksize dd STACKSIZE
  66
  67 section .bss
  68 align 4
  69
  70 init_stack:
  71         resb STACKSIZE