kernel/arch/x86_64/boot/start.s

   1 ;  ZeX/OS
   2 ;  Copyright (C) 2007  Tomas 'ZeXx86' Jedrzejek (zexx86@gmail.com)
   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
  18 ; This is the kernel's entry point. We could either call main here,
  19 ; or we can use this to setup the stack or other nice stuff, like
  20 ; perhaps setting up the GDT and segments. Please note that interrupts
  21 ; are disabled at this point: More on interrupts later!
  22 %macro  IMP 1
  23 %ifdef UNDERBARS
  24         EXTERN _%1
  25         %define %1 _%1
  26 %else
  27         EXTERN %1
  28 %endif
  29 %endmacro
  30
  31 %macro  EXP     1
  32         GLOBAL $_%1
  33         $_%1:
  34         GLOBAL $%1
  35         $%1:
  36 %endmacro
  37
  38 [BITS 32]
  39 global start
  40 start:
  41     mov esp, _sys_stack     ; This points the stack to our new stack area
  42     jmp stublet
  43
  44 ; This part MUST be 4byte aligned, so we solve that issue using 'ALIGN 4'
  45 ALIGN 4
  46 mboot:
  47     ; Multiboot macros to make a few lines later more readable
  48     MULTIBOOT_PAGE_ALIGN        equ 1<<0
  49     MULTIBOOT_MEMORY_INFO       equ 1<<1
  50     MULTIBOOT_AOUT_KLUDGE       equ 1<<16
  51     MULTIBOOT_HEADER_MAGIC      equ 0x1BADB002
  52     MULTIBOOT_HEADER_FLAGS      equ MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_AOUT_KLUDGE
  53     MULTIBOOT_CHECKSUM  equ -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)
  54     EXTERN code, bss, end
  55
  56     ; This is the GRUB Multiboot header. A boot signature
  57     dd MULTIBOOT_HEADER_MAGIC
  58     dd MULTIBOOT_HEADER_FLAGS
  59     dd MULTIBOOT_CHECKSUM
  60
  61     ; AOUT kludge - must be physical addresses. Make a note of these:
  62     ; The linker script fills in the data for these ones!
  63     dd mboot
  64     dd code
  65     dd bss
  66     dd end
  67     dd start
  68
  69 ; This is an endless loop here. Make a note of this: Later on, we
  70 ; will insert an 'extern _main', followed by 'call _main', right
  71 ; before the 'jmp $'.
  72 stublet:
  73
  74     IMP main
  75
  76     push ebx            ; Get to main function data from bootloader
  77
  78     call main
  79     jmp $
  80
  81
  82 ; Here is the definition of our BSS section. Right now, we'll use
  83 ; it just to store the stack. Remember that a stack actually grows
  84 ; downwards, so we declare the size of the data before declaring
  85 ; the identifier '_sys_stack'
  86 SECTION .bss
  87     resb 8192               ; This reserves 8KBytes of memory here
  88 _sys_stack: