[BITS 32]

; Declare constants for the multiboot header.
MBALIGN  equ  1 << 0            ; align loaded modules on page boundaries
MEMINFO  equ  1 << 1            ; provide memory map
MBFLAGS  equ  MBALIGN | MEMINFO ; this is the Multiboot 'flag' field
MAGIC    equ  0x1BADB002        ; 'magic number' lets bootloader find the header
CHECKSUM equ -(MAGIC + MBFLAGS)   ; checksum of above, to prove we are multiboot
 
; Declare a multiboot header that marks the program as a kernel. These are magic
; values that are documented in the multiboot standard. The bootloader will
; search for this signature in the first 8 KiB of the kernel file, aligned at a
; 32-bit boundary. The signature is in its own section so the header can be
; forced to be within the first 8 KiB of the kernel file.
section .multiboot
align 4
	dd MAGIC
	dd MBFLAGS
	dd CHECKSUM

section .bootstrap

present	equ 1 << 7
not_sys	equ 1 << 4
exec	equ 1 << 3
cd		equ 1 << 2
rw		equ 1 << 1
access	equ 1 << 0

gran_4k	equ 1 << 7
sz_32	equ 1 << 6
long_m	equ 1 << 5

global gdt.ptr
gdt:
.null: equ $ - gdt
	dq 0
.code: equ $ - gdt
	dd 0xffff
	db 0
	db present | not_sys | exec | rw
	db gran_4k | long_m | 0xf
	db 0
.data: equ $ - gdt
	dd 0xffff
	db 0
	db present | not_sys | rw
	db gran_4k | sz_32 | 0xf
	db 0
.ptr:
	dw $ - gdt - 1
	dq gdt

global bootstrap
bootstrap:

	mov dword [multiboot_magic], eax
	mov dword [multiboot_header], ebx

	mov eax, cr0
	and eax, ~(1 << 31)
	mov cr0, eax

	mov edi, pml4 ;0x1000
	mov cr3, edi
	xor eax, eax
	mov ecx, 1024
	rep stosd

	mov edi, 0x2000
	mov ecx, 4096
	rep stosd

	mov edi, cr3

	mov dword [edi], 0x2003
	mov edi, 0x2000
	mov dword [edi], 0x3003
	add edi, 0x1000
	mov dword [edi], 0x4003
	mov dword [edi + 8], 0x5003
	add edi, 0x1000

	mov ebx, 0x00000003
	mov ecx, 512

.set_entry:
	mov dword [edi], ebx
	add ebx, 0x1000
	add edi, 8
	loop .set_entry

	mov edi, 0x5000
	mov ecx, 512

.set_entry_2:
	mov dword [edi], ebx
	add ebx, 0x1000
	add edi, 8
	loop .set_entry_2

	mov eax, cr4
	or eax, 1 << 5
	mov cr4, eax

	mov ecx, 0xc0000080
	rdmsr
	or eax, 1 << 8 | 1 << 0
	wrmsr

	mov eax, cr0
	or eax, 1 << 31
	mov cr0, eax

	lgdt [gdt.ptr]

	mov ax, gdt.data
	mov ds, ax
	mov es, ax
	mov fs, ax
	mov gs, ax
	mov ss, ax

	extern start
	jmp gdt.code:start

global set_pml4
set_pml4:
	mov ecx, 0xC000080
	rdmsr
	and eax, ~(1 << 8)
	wrmsr

	mov eax, cr0
	and eax, ~(1 << 31)
	mov cr0, eax

	mov cr3, edi

	mov ecx, 0xC000080
	rdmsr
	or eax, 1 << 8
	wrmsr

	mov eax, cr0
	or eax, 1 << 31
	mov cr0, eax

	retf

section .data
align 16
global multiboot_header
multiboot_header: dq 0
global multiboot_magic
multiboot_magic: dq 0

section .bss
global pml4
align 4096
pml4: resq 512