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
rdtsc(void)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
sigsegv_cb(int sig)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
task(void)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
main(void)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