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path: root/Documentation/prctl/disable-tsc-test.c
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/*
 * Tests for prctl(PR_GET_TSC, ...) / prctl(PR_SET_TSC, ...)
 *
 * Basic test to test behaviour of PR_GET_TSC and PR_SET_TSC
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <inttypes.h>


#include <sys/prctl.h>
#include <linux/prctl.h>

/* Get/set the process' ability to use the timestamp counter instruction */
#ifndef PR_GET_TSC
#define PR_GET_TSC 25
#define PR_SET_TSC 26
# define PR_TSC_ENABLE		1   /* allow the use of the timestamp counter */
# define PR_TSC_SIGSEGV		2   /* throw a SIGSEGV instead of reading the TSC */
#endif

const char *tsc_names[] =
{
	[0] = "[not set]",
	[PR_TSC_ENABLE] = "PR_TSC_ENABLE",
	[PR_TSC_SIGSEGV] = "PR_TSC_SIGSEGV",
};

uint64_t rdtsc() {
uint32_t lo, hi;
/* We cannot use "=A", since this would use %rax on x86_64 */
__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
return (uint64_t)hi << 32 | lo;
}

void sigsegv_cb(int sig)
{
	int tsc_val = 0;

	printf("[ SIG_SEGV ]\n");
	printf("prctl(PR_GET_TSC, &tsc_val); ");
	fflush(stdout);

	if ( prctl(PR_GET_TSC, &tsc_val) == -1)
		perror("prctl");

	printf("tsc_val == %s\n", tsc_names[tsc_val]);
	printf("prctl(PR_SET_TSC, PR_TSC_ENABLE)\n");
	fflush(stdout);
	if ( prctl(PR_SET_TSC, PR_TSC_ENABLE) == -1)
		perror("prctl");

	printf("rdtsc() == ");
}

int main(int argc, char **argv)
{
	int tsc_val = 0;

	signal(SIGSEGV, sigsegv_cb);

	printf("rdtsc() == %llu\n", (unsigned long long)rdtsc());
	printf("prctl(PR_GET_TSC, &tsc_val); ");
	fflush(stdout);

	if ( prctl(PR_GET_TSC, &tsc_val) == -1)
		perror("prctl");

	printf("tsc_val == %s\n", tsc_names[tsc_val]);
	printf("rdtsc() == %llu\n", (unsigned long long)rdtsc());
	printf("prctl(PR_SET_TSC, PR_TSC_ENABLE)\n");
	fflush(stdout);

	if ( prctl(PR_SET_TSC, PR_TSC_ENABLE) == -1)
		perror("prctl");

	printf("rdtsc() == %llu\n", (unsigned long long)rdtsc());
	printf("prctl(PR_SET_TSC, PR_TSC_SIGSEGV)\n");
	fflush(stdout);

	if ( prctl(PR_SET_TSC, PR_TSC_SIGSEGV) == -1)
		perror("prctl");

	printf("rdtsc() == ");
	fflush(stdout);
	printf("%llu\n", (unsigned long long)rdtsc());
	fflush(stdout);

	exit(EXIT_SUCCESS);
}

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