paging

kernel/boot/boot.S

@@ -10,6 +10,13 @@
 .long FLAGS
 .long CHECKSUM
 
+.section .bss
+.align 4096
+boot_page_directory:
+    .skip 4096
+boot_page_table1:
+    .skip 4096
+
 .section .bss
 .align 16
 stack_bottom:

kernel/kmain.c

@@ -53,14 +53,12 @@ void kmain(uint32_t magic, multiboot_info* mbi)  {
   uint32_t mem_size = total_free_memory();
   kprintf("Total available memory: %d MB\n", mem_size / 1024 / 1024);
 
-  page = alloc_page();
-  kprintf("Allocated page at: 0x%x\n", (uint32_t)page);
+  init_paging();
+  enable_paging();
+  kprintf("Paging enabled\n");
 
-  free_page(page);
-  kprintf("Freed page");
-
-  enable_interrupts();
-  kprintf("Interrupts enabled\n");
+  // enable_interrupts();
+  // kprintf("Interrupts enabled\n");
 
   while(1);
 }

kernel/linker.ld

@@ -2,7 +2,7 @@ ENTRY(_start)
 
 SECTIONS
 {
-	. = 2M;
+	. = 0xC0100000;
 	__kernel_start = .;
 
 	.text BLOCK(4K) : ALIGN(4K)

kernel/memory/mm.c

@@ -13,6 +13,8 @@ static uint32_t max_address = 0;
 static uint32_t total_available_memory = 0;
 static uint8_t memory_bitmap[BITMAP_SIZE];
 
+uint32_t* page_directory;
+
 static void mark_free(uint32_t addr) {
     uint32_t page_index = addr / PAGE_SIZE;
     uint32_t byte_index = page_index / 8;
@@ -112,3 +114,19 @@ void* alloc_page() {
 void free_page(void* addr) {
     mark_free((uint32_t)addr);
 }
+
+void init_paging() {
+    page_directory = alloc_page();
+    for (int i = 0; i < 1024; i++) {
+        page_directory[i] = 0x0; 
+    }
+
+    uint32_t* page_table = alloc_page();
+    page_directory[0] = (uint32_t)(page_table) | 0x3;
+    for (int i = 0; i < 1024; i++) {
+        page_table[i] = (i * PAGE_SIZE) | 0x3;
+    }
+
+    extern void load_page_directory(uint32_t* pd);
+    load_page_directory(page_directory);
+}

kernel/memory/mm.h

@@ -13,4 +13,7 @@ uint32_t total_free_memory();
 void* alloc_page();
 void free_page(void* addr);
 
+void init_paging();
+void enable_paging();
+
 #endif 

kernel/memory/mm_stubs.S

@@ -0,0 +1,21 @@
+.code32 
+.global load_page_directory
+load_page_directory: 
+    push %ebp 
+    mov %esp, %ebp 
+    
+    mov 8(%ebp), %eax
+    mov %eax, %cr3
+
+    leave 
+    ret
+
+.global enable_paging
+enable_paging:
+    mov %eax, %cr0
+    orl $0x80000000, %eax
+    mov %cr0, %eax
+    jmp 1f
+1:
+    ret
+