#include <stdio.h>

/*
  Handler for page faults.
*/
void page_fault(registers_t regs){
   // A page fault has occurred.
   // The faulting address is stored in the CR2 register.
   uint32_t faulting_address;
   asm volatile("mov %%cr2, %0" : "=r" (faulting_address));

   // The error code gives us details of what happened.
   int present   = !(regs.err_code & 0x1); // Page not present
   int rw = regs.err_code & 0x2;           // Write operation?
   int us = regs.err_code & 0x4;           // Processor was in user-mode?
   int reserved = regs.err_code & 0x8;     // Overwritten CPU-reserved bits of page entry?
   int id = regs.err_code & 0x10;          // Caused by an instruction fetch?

   // Output an error message.
   printf("Page fault: ( ");
   if (present) {printf("present ");}
   if (rw) {printf("read-only ");}
   if (us) {printf("user-mode ");}
   if (reserved) {printf("reserved ");}
   printf(") at 0x%c\n", faulting_address); // FIXME: fix %c to %X
   printf("PAGE FAULT\n");
}


uint32_t page_directory[1024] __attribute__((aligned(4096)));
uint32_t first_page_table[1024] __attribute__((aligned(4096)));

extern void loadPageDirectory(unsigned int*);
extern void enable_paging();

void init_paging() {
	//set each entry to not present
	int i;
	for(i = 0; i < 1024; i++)
	{
	    // This sets the following flags to the pages:
	    //   Supervisor: Only kernel-mode can access them
	    //   Write Enabled: It can be both read from and written to
	    //   Not Present: The page table is not present
	    page_directory[i] = 0x00000002;
	}

	//we will fill all 1024 entries in the table, mapping 4 megabytes
	for(i = 0; i < 1024; i++)
	{
	    // As the address is page aligned, it will always leave 12 bits zeroed.
	    // Those bits are used by the attributes ;)
	    first_page_table[i] = (i * 0x1000) | 3; // attributes: supervisor level, read/write, present.
	}
	
	// attributes: supervisor level, read/write, present
	page_directory[0] = ((unsigned int)first_page_table) | 3;

   	register_interrupt_handler(14, &page_fault);

	loadPageDirectory(page_directory);
	enable_paging();
}