From f45b2e7c13b3c8821832374e3e8860eabaaae5d2 Mon Sep 17 00:00:00 2001
From: Dennis Kobert <dennis@kobert.dev>
Date: Fri, 25 Oct 2019 02:53:43 +0200
Subject: Initialize paging

---
 kernel/src/boot.asm | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/kernel/src/boot.asm b/kernel/src/boot.asm
index de832f8..3d79096 100644
--- a/kernel/src/boot.asm
+++ b/kernel/src/boot.asm
@@ -74,6 +74,37 @@ check_long_mode:
 	mov al, "2"
 	jmp error
 
+setup_page_tables:
+	; map first P4 entry to P3 table
+    mov eax, p3_table
+    or eax, 0b11 ; present + writable
+    mov [p4_table], eax
+
+    ; map first P3 entry to P2 table
+    mov eax, p2_table
+    or eax, 0b11 ; present + writable
+    mov [p3_table], eax
+	
+	; map each P2 entry to a huge 2MiB page
+    mov ecx, 0         ; counter variable
+    mov eax, 0b10000011 ; present + writable + huge
+
+.map_p2_table:
+    ; map ecx-th P2 entry to a huge page that starts at address 2MiB*ecx
+    mov [p2_table + ecx     ], eax ; map ecx-th entry
+    add eax, 0x200000  ; 2MiB
+    mov [p2_table + ecx + 8 ], eax ; map ecx-th entry
+    add eax, 0x200000  ; 2MiB
+    mov [p2_table + ecx + 16], eax ; map ecx-th entry
+    add eax, 0x200000  ; 2MiB
+    mov [p2_table + ecx + 24], eax ; map ecx-th entry
+    add eax, 0x200000  ; 2MiB
+
+	add ecx, 32
+    cmp ecx, 4096      ; if counter == 512, the whole P2 table is mapped
+    jne .map_p2_table  ; else map the next entry
+
+	ret
 ; Prints 'ERR: ' and the given error code to the screen and halts
 ; parameter: error code letter (ascii) in al
 error:
@@ -84,6 +115,13 @@ error:
 	hlt
 
 section .bss
+align 4096
+p4_table:
+	resb 4096
+p3_table:
+	resb 4096
+p2_table:
+	resb 4096
 stack_bottom:
 	resb 64
 stack_top:
-- 
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