From 25b5eb6c783a76cbc0008f338211c5358890366d Mon Sep 17 00:00:00 2001
From: Adrien Bourmault <neox@os-k.eu>
Date: Wed, 15 Jan 2020 16:26:44 +0100
Subject: [PATCH] Cleanup in boot

---
 boot/loader/mem/management.inc | 39 ++++++++++++++--------------------
 boot/loader/mem/structures.inc |  2 +-
 2 files changed, 17 insertions(+), 24 deletions(-)

diff --git a/boot/loader/mem/management.inc b/boot/loader/mem/management.inc
index dc67950..961478f 100644
--- a/boot/loader/mem/management.inc
+++ b/boot/loader/mem/management.inc
@@ -23,43 +23,36 @@
 ;   along with OS/K.  If not, see <https://www.gnu.org/licenses/>.             ;
 ;=----------------------------------------------------------------------------=;
 
-%define MAX_MEMORY 1 ; GiB
-
 [BITS 32]
 [section .text]
 ; ---------------------------------------------------------------------------- ;
 ;    Constructor for the page tables in protected mode                         ;
 ; ---------------------------------------------------------------------------- ;
 Setup_paging:
-    ;; Map the first PML4 entry to PDP table
+    ;; Map first PML4 entry to PDP table
     mov eax, PDP_table
-    or eax, 1 << 1 | 1 << 0             ; present + writable
+    or eax, 0b11                        ; Present + writable
     mov [PML4_table], eax
 
-    ;; Map the PDP entries to PD tables
-    mov ebx, PD_table                   ; start address
-    mov ecx, 0x0                        ; counter variable
-.map_pdp_table:
-    mov eax, ebx
-    or eax, 1 << 1 | 1 << 0             ; present + writable
-    mov [PDP_table + 8 * ecx], eax
-    inc ecx
-    add ebx, 4096
-    cmp ecx, MAX_MEMORY                 ; PDP table is mapped if MAX_MEMORY
-    jne .map_pdp_table                  ; else map the next entry
+    ;; Map first PDP entry to PD table
+    mov eax, PD_table
+    or eax, 0b11                        ; Present + writable
+    mov [PDP_table], eax
 
-    ;; Map each PD entry to a 'huge' 4MiB page
+    ;; Map each PD entry to a huge 2MiB page
+    mov ecx, 0                          ; counter variable
 
-    mov ecx, 0x0                        ; counter variable
 .map_pd_table:
-    ;; map ecx-th PD entry to a huge page that starts at address 4MiB*ecx
-    mov eax, 0x200000
+    ;; Map ecx-th PD entry to a huge page that starts at address 2MiB*ecx
+    mov eax, 0x200000                   ; 2MiB
     mul ecx                             ; start address of ecx-th page
-    or eax, 1 << 7 | 1 << 1 | 1 << 0    ; present + writable + huge
-    mov [PD_table + ecx * 8], eax
-    inc ecx
-    cmp ecx, 512 * MAX_MEMORY           ; PD table is mapped if 512
+    or eax, 0b10000011                  ; present + writable + huge
+    mov [PD_table + ecx * 8], eax       ; map ecx-th entry
+
+    inc ecx                             ; increase counter
+    cmp ecx, 512                        ; if counter == 512, the whole P2 table is mapped
     jne .map_pd_table                   ; else map the next entry
+
     ret
 
 ; ---------------------------------------------------------------------------- ;
diff --git a/boot/loader/mem/structures.inc b/boot/loader/mem/structures.inc
index 590f651..ebed229 100644
--- a/boot/loader/mem/structures.inc
+++ b/boot/loader/mem/structures.inc
@@ -63,4 +63,4 @@ PML4_table:
 PDP_table:
     resb 4096
 PD_table:
-    times MAX_MEMORY resb 4096
+    resb 4096