From 9172da075af71d4c03cc60267e5acb0ec7d88f31 Mon Sep 17 00:00:00 2001
From: Nigel <nigelbarink@hotmail.com>
Date: Mon, 15 Aug 2022 19:51:22 +0200
Subject: [PATCH] Added identity paging basics

Followed wiki.osdev.org/Setting_Up_Paging
---
 src/kernel/kernel.cpp        | 11 +++--
 src/kernel/memory/paging.cpp | 79 ++++++++++++++++++++++++++++++++----
 src/kernel/memory/paging.h   |  3 --
 3 files changed, 77 insertions(+), 16 deletions(-)

diff --git a/src/kernel/kernel.cpp b/src/kernel/kernel.cpp
index 7d15fcf..12d1c79 100644
--- a/src/kernel/kernel.cpp
+++ b/src/kernel/kernel.cpp
@@ -4,7 +4,7 @@ extern "C" void kernel_main (BootInfo* bootinfo) {
     init_serial();
     pit_initialise();
 
-    InitializePaging();
+    //InitializePaging();
     //Enable();
 
     startSuperVisorTerminal(bootinfo);
@@ -90,8 +90,7 @@ extern "C" void early_main(unsigned long magic, unsigned long addr){
        memAlloc.allocate_region(kernel_end, kernel_end - kernel_begin);
 
         // test alloc_block
-     
-         
+        /*
         uint8_t* memory = (uint8_t*) memAlloc.allocate_block();
         printf("Got a new pointer: 0x%x\n", memory);
 
@@ -102,13 +101,13 @@ extern "C" void early_main(unsigned long magic, unsigned long addr){
         memAlloc.free_block((void*) memory);
 
         uint8_t* newBlockPlse = (uint8_t*) memAlloc.allocate_block();
-        
+        */
 
 
 
        // memAlloc.free_block((void*) memory);
-  
-    
+        InitializePaging();
+        Enable();
     }
     
     initGDT();
diff --git a/src/kernel/memory/paging.cpp b/src/kernel/memory/paging.cpp
index 6f50e3c..9ea4859 100644
--- a/src/kernel/memory/paging.cpp
+++ b/src/kernel/memory/paging.cpp
@@ -1,16 +1,79 @@
 #include "paging.h"
-PageDirectoryEntry kernel_directory[MAX_DIRECTORY_ENTRIES];
+PageDirectoryEntry kernel_directory[MAX_DIRECTORY_ENTRIES]__attribute__((aligned(4096)));
+PageTableEntry first_page_table[1024]__attribute__((aligned(4096)));
+
+#define KERNEL_VRT_MEMORY_BEGIN 0xC0000000
+#define KERNEL_VRT_MEMORY_END   0xCFFFFFFF
+#define PAGE_SIZE  0xFA0;
+
 
 void InitializePaging()
 {
+
+
+    printf("\nInit paging\n");
+    // The basics as explained by wiki.osdev.org
+
+    // Set all page_directories to not present
+    int i = 0;
+    while ( i < 1024)
+    {
+        kernel_directory[i] = 0x00000002;
+        i++;
+    }
+
+
+    // map 4 megabytes 
+    unsigned int j ;
+    for( j = 0;  j < 1024; j++ )
+    {
+        first_page_table[j] = (j * 0x1000) | 3 ;
+        /*
+        Attributes: 
+        Supervisor Level ,
+        read/write,
+        present,
+        */ 
+
+    }
+
+    // Put the page table in the page directory 
+    // attributes: supervisor level, read/write, present;
+    kernel_directory[0] = ((unsigned int)first_page_table) | 3;
+
+    printf("Init paging DONE\n");
+    // NOTE: Adjust this as needed 
+     
+    // BIOS Address Identity mapping 
     // Identity map the first 8MB ... Physical addresses 0x00000000 to 0x007A1200
+    /*
+    
+    PHYSICAL_ADDRESS BIOSAddr = 0x00000000;
+    PHYSICAL_ADDRESS BIOSAddr_Max = 0x007A1200;
+
+    do
+    {
+        Map( BIOSAddr, BIOSAddr, *kernel_directory);
+        BIOSAddr += PAGE_SIZE 
+    } while(BIOSAddr <= BIOSAddr_Max);
+
+    // Identity map the kernel space 
+    VIRTUAL_ADDRESS Vaddr = KERNEL_VRT_MEMORY_BEGIN;
+    PHYSICAL_ADDRESS KernelAddr = kernel_begin;
+
+    do
+    {
+        Map(KernelAddr, Vaddr , *kernel_directory);
+
+        Vaddr += PAGE_SIZE;
+        KernelAddr += PAGE_SIZE 
+
+    }
+    while(KernelAddr < kernel_end);
 
 
-    // Identity map the kernel space || our map to 3GB space
-
-
-    // Identity map VGA memory
-
+    //TODO: Identity map VGA memory
+   */
     
 }
 
@@ -30,9 +93,11 @@ void FreePage(VIRTUAL_ADDRESS vaddr , PageDirectoryEntry& page_directory)
 void Map ( PHYSICAL_ADDRESS paddr, VIRTUAL_ADDRESS vaddr, PageDirectoryEntry& page_directory)
 {
 
+
+
 }
 
-void Unmap(VIRTUAL_ADDRESS, PageDirectoryEntry& page_directory)
+void Unmap(VIRTUAL_ADDRESS vaddr, PageDirectoryEntry& page_directory)
 {
     // NOTE: I will implement lazy unmapping for now 
     
diff --git a/src/kernel/memory/paging.h b/src/kernel/memory/paging.h
index 04aa2fb..789574e 100644
--- a/src/kernel/memory/paging.h
+++ b/src/kernel/memory/paging.h
@@ -12,10 +12,7 @@ void InitializePaging();
 void Enable();
 
 void AllocatePage(VIRTUAL_ADDRESS, PageDirectoryEntry&);
-
-
 void FreePage(VIRTUAL_ADDRESS, PageDirectoryEntry&);
 
-
 void Map(PHYSICAL_ADDRESS, VIRTUAL_ADDRESS, PageDirectoryEntry&);
 void Unmap (VIRTUAL_ADDRESS, PageDirectoryEntry&);