global paging_init

align 4096
page_dir:
  times 4096 db 0

align 4096
page_tables:
  ; two page tables
  times 4096 db 0
  times 4096 db 0
.end:

; here, we initialize paging. since the IDT
; has yet to be populated, we must take extra
; care as we can't afford to trigger a page
; fault.
paging_init:
  push ebp
  mov ebp, esp
  push ebx
  ; populate the page directory
  mov eax, page_tables
  or eax, 0x007
  mov [page_dir], eax
  mov eax, (page_tables+4096)
  or eax, 0x007
  mov [page_dir+4], eax
  ; populate the page tables
  mov ebx, page_tables
  mov ecx, ((page_tables.end-page_tables)/4)
  mov edx, 0
.loop:
  mov eax, edx
  or eax, 0x003
  cmp edx, 0x100000
  jb .skip
  or eax, 0x004
.skip:
  mov [ebx], eax
  dec ecx
  jz .end
  add ebx, 4
  add edx, 4096
  jmp .loop
.end:
  ; load the page directory and enable paging
  mov eax, page_dir
  mov cr3, eax
  mov eax, cr0
  or eax, 0x80000000
  mov cr0, eax
  pop ebx
  pop ebp
  ret