global page_directory
global page_tables
global paging_init
global paging_finish
global KERNEL_MAPPING

KERNEL_MAPPING      equ  0xC0000000
VGABUF              equ  0x000B8000

%define mapped(addr) addr - KERNEL_MAPPING

section .bss
align 4096
page_directory:
resb 1024 * 4
page_tables:
resb 1024 * 1024 * 4

section .bootstrap.text
align 8
paging_init:
    extern kernel_start
    extern kernel_end

paging_load:
    mov edi, mapped(page_tables)
    mov esi, 0
    mov ecx, 1023

paging_cmp:
    cmp esi, kernel_start
    jl paging_add
    cmp esi, mapped(kernel_end)
    jge paging_map

    mov edx, esi
    or edx, 0x003
    mov [edi], edx

paging_add:
    add esi, 4096
    add edi, 4
    loop paging_cmp

paging_map:

    lea eax, mapped(page_directory)
    push eax
    extern setup_pgdir
    call mapped(setup_pgdir)
    add esp, 0x04

    ; map VGA buffer
    mov dword [mapped(page_tables) + 1023 * 4], VGABUF + 0x003

    ; map 8MB for the kernel
    mov dword [mapped(page_directory) + 0 * 4], mapped(page_tables) + 0x003
    mov dword [mapped(page_directory) + 1 * 4], mapped(page_tables) + 0x400000000 + 0x003
    mov dword [mapped(page_directory) + 768 * 4], mapped(page_tables) + 0x003 
    mov dword [mapped(page_directory) + 769 * 4], mapped(page_tables) + 0x400000000 + 0x003 

    ; tell the MMU where the page dir is
    mov ecx, mapped(page_directory)
    mov cr3, ecx

    ; finally init paging
    mov ecx, cr0
    or ecx, 0x80010000
    mov cr0, ecx

    ret

section .text
align 8
paging_finish:
    ; remove the 8MB ident mapping
    mov dword [page_directory + 0 * 4], 0
    mov dword [page_directory + 1 * 4], 0
    mov ecx, cr3
    mov cr3, ecx
    ret