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[EXTERN kmain] ; kmain is defined in kmain.c
[GLOBAL loader] ; making entry point visible to linker
[GLOBAL kernel_pd] ; make kernel page directory visible
[GLOBAL kernel_stack_protector] ; used to detect kernel stack overflow
; higher-half kernel setup
K_HIGHHALF_ADDR equ 0xC0000000
K_PAGE_NUMBER equ (K_HIGHHALF_ADDR >> 22)
; loader stack size
LOADER_STACK_SIZE equ 0x8000 ; 8Kb
; setting up the Multiboot header - see GRUB docs for details
MODULEALIGN equ 1<<0 ; align loaded modules on page boundaries
MEMINFO equ 1<<1 ; provide memory map
FLAGS equ MODULEALIGN | MEMINFO ; this is the Multiboot 'flag' field
MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header
CHECKSUM equ -(MAGIC + FLAGS) ; checksum required
[section .setup]
align 4
multiboot_header:
dd MAGIC
dd FLAGS
dd CHECKSUM
loader:
; setup the boot page directory used for higher-half
mov ecx, kernel_pd
sub ecx, K_HIGHHALF_ADDR ; access its lower-half address
mov cr3, ecx
; Set PSE bit in CR4 to enable 4MB pages.
mov ecx, cr4
or ecx, 0x00000010
mov cr4, ecx
; Set PG bit in CR0 to enable paging.
mov ecx, cr0
or ecx, 0x80000000
mov cr0, ecx
; long jump required
lea ecx, [higherhalf]
jmp ecx
[section .data]
align 0x1000
kernel_pd:
; uses 4MB pages
; identity-maps the first 4Mb of RAM, and also maps them with offset += k_highhalf_addr
dd 0x00000083
times (K_PAGE_NUMBER - 1) dd 0
dd 0x00000083
times (1024 - K_PAGE_NUMBER - 1) dd 0
[section .text]
higherhalf: ; now we're running in higher half
; unmap first 4Mb
mov dword [kernel_pd], 0
invlpg [0]
mov esp, stack_top ; set up the stack
push eax ; pass Multiboot magic number
add ebx, K_HIGHHALF_ADDR ; update the MB info structure so that it is in higher half
push ebx ; pass Multiboot info structure
call kmain ; call kernel proper
hang:
; halt machine should kernel return
cli
hlt
jmp hang
[section .bss]
align 0x1000
kernel_stack_protector:
resb 0x1000 ; as soon as we have efficient paging, we WON'T map this page
stack_bottom:
resb LOADER_STACK_SIZE
stack_top:
; vim: set ts=4 sw=4 tw=0 noet :
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