os/arch/i686/paging.c

#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>

#include <kernel/paging.h>
#include <kernel/tty.h>
#include <debugging.h>
#include <kernel/heap.h>

extern struct x86_Page_Directory boot_page_directory[1024] __attribute__((aligned(4096)));

static struct x86_Page_Table user_code_table[1024] __attribute__((aligned(4096)));
static uint8_t user_code[4096] __attribute__((aligned(4096)));


static struct x86_Page_Table user_data_table[1024] __attribute__((aligned(4096)));
static uint8_t user_data[4096] __attribute__((aligned(4096)));

static struct x86_Page_Table* get_table(uint16_t index) {
    struct x86_Page_Table* table = (struct x86_Page_Table*)((boot_page_directory[index].address << 12) + 0xC0000000);
    return table;
}

static void reload_pages () {
    asm("\
movl %cr3, %ecx; \
movl %ecx, %cr3; \
    ");
}

void set_page_directory_entry(uintptr_t address, struct x86_Page_Table* table) 
{
    boot_page_directory[address >> 22].address = ((uintptr_t)(table) - 0xC0000000) >> 12;
    boot_page_directory[address >> 22].present = true;
    boot_page_directory[address >> 22].read_write = true;
    boot_page_directory[address >> 22].user_supervisor = true;
}

void set_page_table_entry(size_t address, void* ptr)
{
    struct x86_Page_Table* table = (struct x86_Page_Table*)((boot_page_directory[address >> 22].address << 12) + 0xC0000000);

    table[(address >> 12) & 0x3FF].address = (size_t)(ptr - 0xC0000000) >> 12;
    table[(address >> 12) & 0x3FF].present = true;
    table[(address >> 12) & 0x3FF].read_write = true;
    table[(address >> 12) & 0x3FF].user_supervisor = true;
}

struct x86_Page_Table create_table;

void setup_paging() {
    struct x86_Page_Table* kernel = get_table(768);
    uint16_t i = 0;
    while (kernel[i].present == 0) {
        i++;
    }

    terminal_writestring("Kernel Start Page: ");
    print_hex_bytes(&i, 2);
    while (kernel[i].present != 0) {
        i++;
    }

    terminal_writestring("\nKernel End Page: ");
    print_hex_bytes(&i, 2);
    terminal_putchar('\n');

    set_page_directory_entry(0, &user_code_table);

    /*
    user_code_table.address = ((uintptr_t)user_code - 0xC0000000) >> 12;
    user_code_table.present = true;
    user_code_table.read_write = true;
    user_code_table.user_supervisor = true;
    */

    set_page_directory_entry(0x00400000, &user_data_table);

    /*
    user_data_table.address = ((uintptr_t)user_data - 0xC0000000) >> 12;
    user_data_table.present = true;
    user_data_table.read_write = true;
    user_data_table.user_supervisor = true;
    */

    reload_pages();
}