blob: 047b326b08b6a381fcfbf5e666ac30f29ca71f8c [file] [log] [blame]
;;; GRUB Multiboot header, calls main() in main.c
;; Some constants
MBOOT_PAGE_ALIGN equ 1<<0
MBOOT_MEM_INFO equ 1<<1
MBOOT_HEADER_MAGIC equ 0x1BADB002
MBOOT_HEADER_FLAGS equ MBOOT_PAGE_ALIGN | MBOOT_MEM_INFO
MBOOT_CHECKSUM equ -(MBOOT_HEADER_MAGIC + MBOOT_HEADER_FLAGS)
;; Kernel memory start
KERNEL_VIRTUAL_BASE equ 0xC0000000
;; Index in page directory
KERNEL_PAGE_NUMBER equ (KERNEL_VIRTUAL_BASE >> 22)
STACK_SIZE equ 0x4000
;;;;;;;;;;;;;;;;;;;;; DATA ;;;;;;;;;;;;;;;;;;;;;
[section .data align = 0x1000]
page_directory:
dd 0b010000011 ; Identity map first 4 megs
times (KERNEL_PAGE_NUMBER - 1) dd 0
dd 0b010000011 ; Map kernel memory to zero page too
times (1024 - KERNEL_PAGE_NUMBER - 1) dd 0
gdt:
;; First entry, null segment
dw 0 ; zero limit
dw 0 ; base low
db 0 ; base middle
db 0 ; access
db 0 ; granularity
db 0 ; base high
;; Second entry, code segment
dw 0xffff ; max limit
dw 0
db 0
db 0x9a ; access
db 0xcf ; granularity
db 0
;; Third entry, data segment
dw 0xffff ; max limit
dw 0
db 0
db 0x92 ; access
db 0xcf ; granularity
db 0
;; Fourth entry, user code segment
dw 0xffff ; max limit
dw 0
db 0
db 0xfa ; access
db 0xcf ; granularity
db 0
;; Fifth entry, user data segment
dw 0xffff ; max limit
dw 0
db 0
db 0xf2 ; access
db 0xcf ; granularity
db 0
gdt_pointer:
dw (8 * 5 - 1) ; sizeof(gdt entry) * 5 - 1
dd (gdt - KERNEL_VIRTUAL_BASE) ; Remember, PHYSICAL address
;;;;;;;;;;;;;;;;;;;;; CODE ;;;;;;;;;;;;;;;;;;;;;
[bits 32]
[section .text]
[global mboot]
[extern code]
[extern bss]
[extern end]
mboot:
dd MBOOT_HEADER_MAGIC ; This tells GRUB to start executing here:
dd MBOOT_HEADER_FLAGS
dd MBOOT_CHECKSUM
dd mboot ; Current location
dd code ; .text section
dd bss ; End of .data
dd end ; End of kernel
dd start
[global start]
[extern kmain] ; C code
start equ (_start)
_start:
;; First set up GDT
mov eax, (gdt_pointer - KERNEL_VIRTUAL_BASE)
lgdt [eax] ; Load GDT
mov ax, 0x10 ; Offset of data segment
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
enable_paging:
mov ecx, (page_directory - KERNEL_VIRTUAL_BASE) ; Physical address
mov cr3, ecx
mov ecx, cr4
or ecx, 0x00000010 ; Enable 4 meg pages
mov cr4, ecx
mov ecx, cr0
or ecx, 0x80000000 ; Enable paging
mov cr0, ecx
lea ecx, [in_higher_half] ; Long jump into high memory
jmp ecx
in_higher_half:
mov dword [page_directory], 0
invlpg [0] ; Clear identity mapping
mov esp, (stack + STACK_SIZE)
add ebx, 0xC0000000 ; Translate to virtual address
push ebx ; Holds multiboot header location
push esp ; Initial kernel stack
call kmain
.end:
hlt
jmp .end
[section .bss align = 32]
stack:
resb STACK_SIZE