1/*
2 * Tests for prctl(PR_GET_TSC, ...) / prctl(PR_SET_TSC, ...)
3 *
4 * Tests if the control register is updated correctly
5 * when set with prctl()
6 *
7 * Warning: this test will cause a very high load for a few seconds
8 *
9 */
10
11#include <stdio.h>
12#include <stdlib.h>
13#include <unistd.h>
14#include <signal.h>
15#include <inttypes.h>
16#include <wait.h>
17
18
19#include <sys/prctl.h>
20#include <linux/prctl.h>
21
22/* Get/set the process' ability to use the timestamp counter instruction */
23#ifndef PR_GET_TSC
24#define PR_GET_TSC 25
25#define PR_SET_TSC 26
26# define PR_TSC_ENABLE		1   /* allow the use of the timestamp counter */
27# define PR_TSC_SIGSEGV		2   /* throw a SIGSEGV instead of reading the TSC */
28#endif
29
30/* snippet from wikipedia :-) */
31
32static uint64_t rdtsc(void)
33{
34uint32_t lo, hi;
35/* We cannot use "=A", since this would use %rax on x86_64 */
36__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
37return (uint64_t)hi << 32 | lo;
38}
39
40int should_segv = 0;
41
42static void sigsegv_cb(int sig)
43{
44	if (!should_segv)
45	{
46		fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
47		exit(0);
48	}
49	if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
50	{
51		perror("prctl");
52		exit(0);
53	}
54	should_segv = 0;
55
56	rdtsc();
57}
58
59static void task(void)
60{
61	signal(SIGSEGV, sigsegv_cb);
62	alarm(10);
63	for(;;)
64	{
65		rdtsc();
66		if (should_segv)
67		{
68			fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
69			exit(0);
70		}
71		if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
72		{
73			perror("prctl");
74			exit(0);
75		}
76		should_segv = 1;
77	}
78}
79
80
81int main(int argc, char **argv)
82{
83	int n_tasks = 100, i;
84
85	fprintf(stderr, "[No further output means we're allright]\n");
86
87	for (i=0; i<n_tasks; i++)
88		if (fork() == 0)
89			task();
90
91	for (i=0; i<n_tasks; i++)
92		wait(NULL);
93
94	exit(0);
95}
96
97