LECTURE/ECRITURE DES MSR (MODEL SPECIFIC REGISTER) EN C SOUS LINUX

/* Programme d'écriture de MSR - Utilise l'interface kernel 	*/
/* Donc que le support soit compilé dans le noyau ou que le 	*/
/* module msr soit chargé (modprobe msr) 			*/

/* D'après /usr/src/linux/arch/i386/kernel/msrc.c :		*/

/*
 * msr.c
 *
 * x86 MSR access device
 *
 * This device is accessed by lseek() to the appropriate register number
 * and then read/write in chunks of 8 bytes.  A larger size means multiple
 * reads or writes of the same register.
 *
 * This driver uses /dev/cpu/%d/msr where %d is the minor number, and on
 * an SMP box will direct the access to CPU %d.
 */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>



int main(int argc, char **argv)
{
	unsigned long long int value;
	unsigned int number;
	int fd;

	printf("Write MSR - Write Specifc Model Register\n");
 
	if(argc < 3)
	{
		fprintf(stderr,"\nUsage : %s <MSR number> <value>\nValues MUST be given in Hexadecimal format\n",argv[0]);
		exit(0);
	}
	
	sscanf(argv[1],"%x",&number);
	sscanf(argv[2],"%Lx",&value);

	printf("MSR number :\t0x%x\nMSR value :\t0x%Lx\n",number,value);

	if(setuid(0) != 0)	// On prend les droits root pour pouvoir ouvrir le fichier
	{
		fprintf(stderr, "\nYou must be root to run this program or have the setuid bit set.\n");
		exit(-1);
	}
	
	if((fd = open("/dev/cpu/0/msr",O_WRONLY)) == -1)
	{
		fprintf(stderr,"\nOpen error on /dev/cpu/0/msr\n");
		exit(-1);
	}
	if(lseek(fd,number,SEEK_SET) == -1)
	{
		fprintf(stderr,"\nSeek error in /dev/cpu/0/msr\n");
		exit(-1);
	}
	if(write(fd,&value,8) != 8)
	{
		fprintf(stderr,"\nWrite error in /dev/cpu/0/msr\n");
		exit(-1);
	}
	close(fd);
	return 0;
}