From d71f2d4abc385d4aee1b1a9c9a8924379b471380 Mon Sep 17 00:00:00 2001
From: Baptiste Wicht <baptiste.wicht@gmail.com>
Date: Thu, 10 Oct 2013 17:57:18 +0200
Subject: [PATCH] Prototype of switching to long mode

---
 src/kernel.asm | 129 +++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 115 insertions(+), 14 deletions(-)

diff --git a/src/kernel.asm b/src/kernel.asm
index 4d5db788..ac8bb225 100644
--- a/src/kernel.asm
+++ b/src/kernel.asm
@@ -6,34 +6,135 @@ jmp _start
 
 _start:
     ; Set stack space
-	mov ax, 0x9000
-	mov ss, ax
-	mov sp, 0xffff
+    mov ax, 0x9000
+    mov ss, ax
+    mov sp, 0xffff
 
     ; Set data segment
-	mov ax, 0x100
-	mov ds, ax
+    mov ax, 0x100
+    mov ds, ax
 
     call new_line_16
 
-	mov si, kernel_header_0
-	call print_line_16
+    mov si, kernel_header_0
+    call print_line_16
 
     mov si, kernel_header_1
-	call print_line_16
+    call print_line_16
 
     mov si, kernel_header_2
-	call print_line_16
+    call print_line_16
 
     call new_line_16
 
+    ; Disable interrupts
+    cli
+
+    ; Load GDT
+    lgdt [GDT64]
+
+    ; Switch to protected mode
+    mov eax, cr0
+    or al, 1b
+    mov cr0, eax
+
+    ; Desactivate pagination
+    mov eax, cr0
+    and eax, 01111111111111111111111111111111b
+    mov cr0, eax
+
+    jmp (CODE_SELECTOR-GDT64):pm_start
+
+[BITS 32]
+
+pm_start:
+
+    ; Update segments
+    mov ax, DATA_SELECTOR-GDT64
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    mov ss, ax
+
+    ; Activate PAE
+    mov eax, cr4
+    or eax, 100000b
+    mov cr4, eax
+
+    ; Clean pages
+    mov edi, 0x70000
+    mov ecx, 0x10000
+    xor eax, eax
+    rep stosd
+
+    ; Update pages
+    mov     dword [0x70000], 0x71000 + 7    ; first PDP table
+    mov     dword [0x71000], 0x72000 + 7    ; first page directory
+    mov     dword [0x72000], 0x73000 + 7    ; first page table
+
+    mov     edi, 0x73000                    ; address of first page table
+    mov     eax, 7
+    mov     ecx, 256                        ; number of pages to map (1 MB)
+
+    make_page_entries:
+        stosd
+        add     edi, 4
+        add     eax, 0x1000
+        loop    make_page_entries
+
+    ; Copy PML4 address into cr3
+    mov     eax, 0x70000    ; Bass address of PML4
+    mov     cr3, eax        ; load page-map level-4 base
+
+    ; Switch to long mode
+
+    mov eax, cr0
+    or eax, 10000000000000000000000000000000b
+    mov cr0, eax
+
+    jmp (LONG_SELECTOR-GDT64):lm_start
+
+[BITS 64]
+
+lm_start:
+
     jmp $
 
 ; Datas
 
-	kernel_header_0 db '******************************', 0
-	kernel_header_1 db 'Welcome to Thor OS!', 0
-	kernel_header_2 db '******************************', 0
+    kernel_header_0 db '******************************', 0
+    kernel_header_1 db 'Welcome to Thor OS!', 0
+    kernel_header_2 db '******************************', 0
 
-    ; Fill the sector (not necessary, but cleaner)
-	times 512-($-$$) db 0
+GDT64:
+    NULL_SELECTOR:
+        dw GDT_LENGTH   ; limit of GDT
+        dw GDT64        ; linear address of GDT
+        dd 0x0
+
+    CODE_SELECTOR:          ; 32-bit code selector (ring 0)
+        dw 0x0FFFF
+        db 0x0, 0x0, 0x0
+        db 10011010b
+        db 11001111b
+        db 0x0
+
+    DATA_SELECTOR:          ; flat data selector (ring 0)
+        dw  0x0FFFF
+        db  0x0, 0x0, 0x0
+        db  10010010b
+        db  10001111b
+        db  0x0
+
+    LONG_SELECTOR:  ; 64-bit code selector (ring 0)
+        dw  0x0FFFF
+        db  0x0, 0x0, 0x0
+        db  10011010b       ;
+        db  10101111b
+        db  0x0
+
+   GDT_LENGTH:
+
+   ; Fill the sector (not necessary, but cleaner)
+   times 512-($-$$) db 0