1 global loader ; making entry point visible to linker

2 extern kmain ; main is defined elsewhere

3

4 ; setting up the Multiboot header - see GRUB docs for details

5 MODULEALIGN equ 1<<0 ; align loaded modules on page

6 ; boundaries

7 MEMINFO equ 1<<1 ; provide memory map

8 FLAGS equ MODULEALIGN | MEMINFO ; this is the Multiboot 'flag' field

9 MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header

10 CHECKSUM equ -(MAGIC + FLAGS) ; checksum required

11

12 section .multiboot

13 align 4

14 MultiBootHeader:

15 dd MAGIC

16 dd FLAGS

17 dd CHECKSUM

18

19 ; reserve initial kernel stack space

20 STACKSIZE equ 0x4000 ; that's 16k.

21

22 loader:

23 mov esp, stack+STACKSIZE ; set up the stack

24 push eax ; pass Multiboot magic number

25 push ebx ; pass Multiboot info structure

26 call kmain ; call kernel proper

27 cli

28 hang:

29 hlt ; halt machine should kernel return

30 jmp hang

31

32 section .bss

33 align 32

34 stack:

35 resb STACKSIZE ; reserve stack on a quadword boundary