[BITS 32]

MODULEALIGN     equ 1<<0
MEMINFO         equ 1<<1
AOUTKLUDGE      equ 1<<16
FLAGS           equ MODULEALIGN | MEMINFO | AOUTKLUDGE
MAGIC           equ 0x1badb002
CHECKSUM        equ -(MAGIC + FLAGS)

section .text
align 4
MULTIBOOTHEADER:
MultiBootHeader:
        dd MAGIC
        dd FLAGS
        dd CHECKSUM

        dd MULTIBOOTHEADER - 0x00000010 + 0x00100000
        dd $$ - 0x00000010 + 0x00100000
        dd BOOTLOADER_END - 0x00000010 + 0x00100000
        dd BSS_END - 0x00000010 + 0x00100000
        dd START - 0x00000010 + 0x00100000

STACKSIZE equ 0x1000

START:
        mov eax, cr0                                    ; disable old paging before we set up our new one
        and eax, 01111111111111111111111111111111b
        mov cr0, eax

        mov edi, 0x1000                                 ; clear space for the paging tables
        mov cr3, edi                                    ; set cr3 to edi ?????????????
        xor eax, eax
        mov ecx, 4096
        rep stosd
        mov edi, cr3                                    ; edi now contains address of PML4T

        mov dword[edi], 0x2003                          ; set PML4T to point to PDPT
        add edi, 0x1000

        mov dword[edi], 0x3003                          ; set PDPT to point to PDT
        add edi, 0x1000

        mov dword[edi], 0x4003                          ; set PDT to point to PT
        add edi, 0x1000

        mov ebx, 0x3
        mov ecx, 512

.setEntry:                                              ; we want to map the first two MiB
        mov dword[edi], ebx                             ; 0x0003 on first run i.e. present and r/w
        add ebx, 0x1000                                 ; move to next page
        add edi, 8                                      ; move to next entry in PT
        loop .setEntry                                  ; and loop until we are done

        mov eax, cr4                                    ; enable PAE-paging
        or eax, 1<<5
        mov cr4, eax

        mov ecx, 0xc0000080                             ; set the LM-bit
        rdmsr
        or eax, 1<<8
        wrmsr

        mov eax, cr0                                    ; re-enable paging from when we disabled it at the beginning
        or eax, 1<<31
        mov cr0, eax

;       jmp $

        lgdt [GDT64.Pointer]                            ; load our simple GDT

;       jmp $

        jmp GDT64.Code:start64                          ; and jump into 64-bit code

GDT64:                                                  ; Global Descriptor Table (64-bit).
.Null: equ $ - GDT64                                    ; The null descriptor.
        dw 0                                            ; Limit (low).
        dw 0                                            ; Base (low).
        db 0                                            ; Base (middle)
        db 0                                            ; Access.
        db 0                                            ; Granularity.
        db 0                                            ; Base (high).
        .Code: equ $ - GDT64                            ; The code descriptor.
    dw 0                         ; Limit (low).
    dw 0                         ; Base (low).
    db 0                         ; Base (middle)
    db 10011000b                 ; Access.
    db 00100000b                 ; Granularity.
    db 0                         ; Base (high).
;       dq 00000000b,0b,0b,1b,0b,0000b,1b,00b,1b,1b,0b,0b,0b,00000000b,00000000b,00000000b,00000000b,00000000b
.Data: equ $ - GDT64                                    ; The data descriptor.
        dq 0x0000900000000000
.Pointer:                                               ; The GDT-pointer.
        dw $ - GDT64 - 1                                ; Limit.
        dq GDT64                                        ; Base.

[BITS 64]
start64:
        cli
        mov ax, GDT64.Data
        mov ds, ax
        mov es, ax
        mov fs, ax
        mov gs, ax
        mov edi, 0xb8000
        mov rax, 0x1f201f201f201f20
        mov ecx, 500
        rep movsq
stublet:
        hlt
        jmp stublet

BOOTLOADER_END:
BSS_START:
section .bss
align 4
stack:
        resb STACKSIZE
BSS_END: