OSDev.org

Code: Select all

pde_t *page_directory;
pte_t *page_table;

/*
 * Initialize virtual memory by building page tables
 * for the kernel and physical memory.
 */
void Init_VM(struct Boot_Info *bootInfo)
{
    /*
     * Hints:
     * - Build kernel page directory and page tables
     * - Call Enable_Paging() with the kernel page directory
     * - Install an interrupt handler for interrupt 14,
     *   page fault
     * - Do not map a page at address 0; this will help trap
     *   null pointer references
     */

    Print("Initializing Paging...\n");

    uint_t totalPages = bootInfo->memSizeKB / 4;
    Print("Pages Required: %d\n", totalPages);

    page_directory = (pde_t *)Alloc_Page();
    Print("Page Directory At:  %d\n", page_directory);

    int reservePages = totalPages * sizeof(pte_t) / 4096;
    Print("Page Tables Will Take: %d pages\n", reservePages);

    page_table = (pte_t *)Alloc_Page();

    int i;
    for (i = 0; i < reservePages - 1; i++)
      Alloc_Page();

    uint_t addr = page_table + (reservePages * 4096);
    for (i = 0; i < totalPages; i++)
    {
        page_table[i].flags = 3;
        page_table[i].pageBaseAddr = addr;
        addr += 4096;
    }

    page_directory[0].flags = 3;
    page_directory[0].pageTableBaseAddr = page_table;

    Install_Interrupt_Handler(14, Page_Fault_Handler);

    checkPaging();
    Enable_Paging(page_directory);
    checkPaging();
}