//-------------------------------------------------------------------
//	showpdir.cpp
//
//	This application uses a pair of installable kernel modules,
//	named 'cr3.c' and 'dram.c', to obtain the value in register
//	CR3, and then use it to read in this task's page-directory.  
//	The address and contents of the page-directory are shown in
//	hexadecimal format (the number of page-tables being used by
//	this task is also shown).
//	
//	Note that 'root' privileges are normally needed, to install 
//	kernel modules or to create device-nodes, like this:
//	
//		root#  /bin/mknod /dev/dram c 253 0
//		root#  /sbin/insmod dram.o
//		root#  /sbin/insmod cr3.o
//
//	NOTE: Written and tested using Linux kernel version 2.4.21.
//
//	programmer: ALLAN CRUSE
//	written on: 21 APR 2004
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), close() 

char devname[] = "/dev/dram";		// name of the 'device' file
char filname[] = "/proc/cr3";		// name of /proc pseudo-file

int main( int argc, char **argv )
{
	// install device-driver modules in the kernel
	system( "/sbin/insmod dram.o" );
	system( "/sbin/insmod cr3.o" );
	
	// get physical address of this task's page-directory 
	int	fd = open( filname, O_RDONLY );
	char	inbuf[ 20 ] = "";
       	if ( read( fd, inbuf, 16 ) < 12 ) { perror( filname ); exit(1); }	
	unsigned long	cr3 = strtol( inbuf+4, 0, 16 ) & 0xFFFFF000;
	close( fd );

	// report physical address of the page-directory
	printf( "\npage-directory at %08X \n", cr3 );

	// open device file for reading from physical memory 
	fd = open( devname, O_RDONLY );
	if ( fd < 0 ) { perror( devname ); exit(1);}

	// read this task's page-directory 
	unsigned long	pgdir[ 1024 ];
	lseek( fd, cr3, SEEK_SET );
	if ( read( fd, pgdir, 4096 ) < 4096 ) { perror( devname ); exit(1); }
	close( fd );
	
	// display the page-directory entries
	for (int i = 0; i < 1024; i++)
		{
		if ( ( i % 8 ) == 0 ) printf( "\n%03X: ", i*4 );
		printf( "%08X ", pgdir[ i ] );
		}
	printf( "\n" );
	
	// count the number of 4KB pages which are 'present'
	int	present = 0;
	for (int i = 0; i < 1024; i++) 
		if ( ( pgdir[ i ] & 0x101 ) == 0x001 ) ++present;
	printf( "\nNumber of page-tables = %d \n", present );
	printf( "\n" );	
}