/*
 * writereg.c
 * 
 *
 * Copyright (C) 2010 - Maxim Levitsky
 *
 *  is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 *  is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with ; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, 
 * Boston, MA  02110-1301  USA
 */


#define _LARGEFILE64_SOURCE
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

#include <sys/mman.h>


#define PAGE_SIZE 4096



int usage()
{
	printf("Usage (as root): writemem address[.width] value\n");
	exit(-1);
}

int get_mem_fd()
{
	int fd = open ("/dev/mem", O_RDWR);

	if( fd == -1) {
		perror("open");
		printf("are you root?\n");
		exit(-1);
	}
	return fd;
}



int main (int argc, char** argv)
{

	/* Test input arg count */
	if (argc != 3 )
		usage();


	int fd = get_mem_fd();
	char *ptr;




	/* Read the register we need to modify */
	off64_t  offset = (off64_t)strtoull (argv[1], &ptr, 0);
	int width = 32;

	if(*ptr == '.') {
		ptr++;

		switch(*ptr) {
		case 'B':
		case 'b':
			width = 8;
			ptr++;
			break;
		case 'W':
		case 'w':
			width = 16;
			ptr++;
			break;
		case 'D':
		case 'd':
			width = 32;
			ptr++;
			break;
		}
	}


	/* read the value */
	uint32_t value  = strtoull (argv[2], &ptr, 0);



	off64_t page_offset = offset & ~(PAGE_SIZE -1);
	int byte_offset = offset - page_offset;
	unsigned char* mem = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_SHARED, fd, page_offset);
	if (mem == 0)
		abort();

	mem+=byte_offset;

	printf("writing %lx to 0x%lx (current value = %lx)\n", (long unsigned int)value, (long unsigned int)offset, (long unsigned int)*(uint32_t*)(mem));

	switch (width) {
	case 32:
		*(uint32_t*)(mem) = value;
		break;
	case 16:
		*(uint16_t*)(mem) = value;
		break;
	case 8:
		*(uint8_t*)(mem) = value;
		break;
	}
	return 0;
}