Added initial paging support.

Makefile

@@ -2,7 +2,7 @@ CFLAGS = -m32 -mgeneral-regs-only -nostdlib -fno-builtin -fno-exceptions -fno-le
 LDFLAGS = 
 
 DISK_IMG_FILES = kernel.bin
-KERNEL32_OBJS = screenstuff.o io.o idt.o keyboard.o strings.o atapio.o c_code_entry.o kernel.o
+KERNEL32_OBJS = screenstuff.o io.o idt.o keyboard.o strings.o atapio.o c_code_entry.o kernel.o paging.o
 
 run: disk.img
 	qemu-system-x86_64 disk.img
@@ -26,7 +26,7 @@ boot.sector: boot.asm
 boot.stage2: boot_stage2.ld boot.stage2.o
 	ld $(LDFLAGS) -T $< boot.stage2.o
 
-boot.stage2.o: src/boot_stage2/main.c io.o atapio.o strings.o c_code_entry.o screenstuff.o
+boot.stage2.o: src/boot_stage2/main.c io.o atapio.o strings.o c_code_entry.o screenstuff.o paging.o
 	gcc $(CFLAGS) -o $@ -c $<
 
 %.bin: %.asm

boot_stage2.ld

@@ -1,7 +1,7 @@
 OUTPUT_FORMAT(binary)
 OUTPUT_ARCH(i386:i386)
 
-INPUT(io.o atapio.o strings.o c_code_entry.o screenstuff.o)
+INPUT(io.o atapio.o strings.o c_code_entry.o screenstuff.o paging.o)
 OUTPUT(boot.stage2)
 
 SECTIONS {

kernel.ld

@@ -4,7 +4,7 @@ OUTPUT_ARCH(i386:i386)
 OUTPUT(kernel.bin)
 
 SECTIONS {
-  . = 0x80000;
+  . = 0xc0000000;
 
   .text : { 
     c_code_entry.o(.text)

src/boot_stage2/main.c

@@ -1,5 +1,6 @@
 #include "../kernel/atapio.h"
 #include "../kernel/screenstuff.h"
+#include "../kernel/paging.h"
 
 typedef struct {
   uint32_t base_low;
@@ -10,6 +11,8 @@ typedef struct {
   uint32_t acpi3_extended;
 }__attribute__((packed)) e820entry;
 
+uint8_t* bitmap = 0x100000;
+
 void set_bit(uint32_t offset, uint8_t* buffer) {
   uint32_t index = offset / 8;
   uint32_t bit = offset % 8;
@@ -17,6 +20,33 @@ void set_bit(uint32_t offset, uint8_t* buffer) {
   buffer[index] |= (1<<(7 - bit));
 }
 
+void unset_bit(uint32_t offset, uint8_t* buffer) {
+  uint32_t index = offset / 8;
+  uint32_t bit = offset % 8;
+
+  buffer[index] &= (255 - (1<<(7 - bit)));
+}
+
+void memset(uint8_t* base, uint32_t count, uint8_t to) {
+  for (int i=0; i<count; i++) {
+    base[i] = to;
+  }
+}
+
+void mark_unavailble(uint32_t address, uint32_t size) {
+  // This function takes an address and length and marks the corresponding pages as unavailable.
+  address -= address % 4096; 
+  if (size % 4096)
+    size += 4096 - (size % 4096);
+
+  address /= 4096;
+  size /= 4096;
+
+  for (int i=0; i<size; i++) {
+    unset_bit(address + i, bitmap);
+  }
+}
+
 void main() {
   init_term();
   init_atapio();
@@ -24,11 +54,8 @@ void main() {
   // e820 memory map exists at 0x20000
   e820entry* e820_entries = 0x20000;
 
-    uint8_t* bitmap = 0x100000;
-
   // Zero out the bitmap.
-    for (int i=0; i<0x20000; i++)
+  memset(bitmap, 0x20000, 0);
-        bitmap[i] = 0;
   // Ensure the bitmap data is clear
 
   for (int i=0; i<0x20000; i++)
@@ -58,18 +85,54 @@ void main() {
     printf("Page Index: %d\nLength (Pages): %d\n", page_index, length / 4096);
 
     for (int j=0; length > 4096; length -= 4096, j++) {
-            uint32_t index = (page_index+j) / 8;
+      set_bit(page_index + j, bitmap);
-            uint32_t bit = (page_index+j) % 8;
-
-            bitmap[index] |= (1<<(7 - bit));
     }
   }
 
-    uint8_t* kernel_location = 0x80000;
+  mark_unavailble(bitmap, 0x20000);
+
+  // Page Directory
+  PDE* kernel_page_directory = bitmap + 0x20000;
+  // Clear the PD 
+  memset((uint8_t*)kernel_page_directory, 4096, 0);
+
+  // Clear 4MB of RAM from 0x121000 to 0x521000 for the 1024 page tables
+  memset((uint8_t*)0x121000, 0x400000, 0);
+
+  // Construct a 1024 long PTE** at 0x521000
+  for (int i=0; i<1024; i++) {
+    ((uint32_t*)0x521000)[i] = 0x121000 + 0x1000*i;
+  }
+
+  PTE** kernel_page_tables = 0x521000;
+
+  // Mark unavailable bitmap to 0x522000
+  mark_unavailble(bitmap, 0x522000 - (uint32_t)bitmap);
+
+  // Now we want to map some stuff.
+  // But first, we should load the kernel somewhere
+
+  uint8_t* kernel_location = 0x522000; // Just load it at 0x522000 for now
+  mark_unavailble(0x522000, 32768); // Just treat the kernel as not growing beyong 32k for now.
+
+  map_many_4k_phys_to_virt(0x522000, 0xc0000000, kernel_page_directory, kernel_page_tables, 8); // Map 8 pages from 0x522000 to 0xc0000000;
+  map_4k_phys_to_virt((uint32_t)kernel_page_directory, 0xc0100000, kernel_page_directory, kernel_page_tables); // Map the page directory to 0xc0100000
+  map_many_4k_phys_to_virt(0x121000, 0xc0101000, kernel_page_directory, kernel_page_tables, 1024); // Map 1024 pages from 0x121000 to 0xc0101000
+  map_4k_phys_to_virt(0xb8000, 0xc0501000, kernel_page_directory, kernel_page_tables); // Map 0xb8000 (video) to 0xc0501000
+
+  map_4k_phys_to_virt(0x8000, 0x8000, kernel_page_directory, kernel_page_tables);
+
   load_file("KERNEL  BIN", kernel_location);
 
   printf("Stage2 success!\n");
 
+  asm ("mov %0, %%eax;" 
+       "mov %%eax, %%cr3" : : "m" (kernel_page_directory));
+
+  asm ("mov %cr0, %eax;"
+       "or $0x80000001, %eax;"
+       "mov %eax, %cr0");
+
   while (1);
-    ((void(*)(void))kernel_location)();
+  ((void(*)(void))0xc0000000)();
 }

src/kernel/paging.c

@@ -0,0 +1,41 @@
+#include "paging.h"
+
+void map_4k_phys_to_virt(uint32_t physical, uint32_t virtual, PDE* page_directory, PTE** page_tables) {
+  uint32_t pd_index = (virtual & (1023 << 20)) >> 20;
+  uint32_t pt_index = (virtual & (1023 << 10)) >> 10;
+
+  page_directory[pd_index] = (PDE){
+    .address = (uint32_t)(page_tables[pd_index]) >> 12,
+    .available = 0,
+    .page_4mb = 0,
+    .accessed = 0,
+    .disable_cache = 0,
+    .write_through_cache = 0,
+    .privilege = 0,
+    .present = 1,
+    .read_write = 1,
+
+    .ignored = 0,
+    .ignored2 = 0
+  };
+
+  page_tables[pd_index][pt_index] = (PTE){
+    .address = physical >> 12,
+    .available = 0,
+    .global = 0,
+    .accessed = 0,
+    .disable_cache = 0,
+    .dirty = 0,
+    .write_through_cache = 0,
+    .privilege = 0,
+    .present = 1,
+    .read_write = 1,
+
+    .ignored = 0
+  };
+}
+
+void map_many_4k_phys_to_virt(uint32_t physical, uint32_t virtual, PDE* page_directory, PTE** page_tables, uint32_t count) {
+  for (int i=0; i<count; i++)
+    map_4k_phys_to_virt(physical + 4096*i, virtual + 4096*i, page_directory, page_tables);
+}

src/kernel/paging.h

@@ -0,0 +1,37 @@
+#ifndef PAGING_H
+#define PAGING_H
+
+#include <stdbool.h>
+#include "types.h"
+
+typedef struct {
+  uint32_t address : 20;
+  uint32_t available : 3;
+  uint32_t ignored : 1;
+  uint32_t page_4mb : 1;
+  uint32_t ignored2 : 1;
+  uint32_t accessed : 1;
+  uint32_t disable_cache : 1;
+  uint32_t write_through_cache : 1;
+  uint32_t privilege : 1;
+  uint32_t read_write : 1;
+  uint32_t present : 1;
+}__attribute__((packed)) PDE;
+
+typedef struct {
+  uint32_t address : 20;
+  uint32_t available : 3;
+  uint32_t global : 1;
+  uint32_t ignored : 1;
+  uint32_t dirty : 1;
+  uint32_t accessed : 1;
+  uint32_t disable_cache : 1;
+  uint32_t write_through_cache : 1;
+  uint32_t privilege : 1;
+  uint32_t read_write : 1;
+  uint32_t present : 1;
+}__attribute__((packed)) PTE;
+
+void map_4k_phys_to_virt(uint32_t physical, uint32_t virtual, PDE* page_directory, PTE** page_tables);
+void map_many_4k_phys_to_virt(uint32_t physical, uint32_t virtual, PDE* page_directory, PTE** page_tables, uint32_t count);
+#endif