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 
32 static uint64_t rdtsc(void)
33 {
34 uint32_t lo, hi;
35 /* We cannot use "=A", since this would use %rax on x86_64 */
36 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
37 return (uint64_t)hi << 32 | lo;
38 }
39 
40 int should_segv = 0;
41 
42 static 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 
59 static 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 
81 int main(void)
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