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disable-tsc-on-off-stress-test.c
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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 
33 uint32_t lo, hi;
34 /* We cannot use "=A", since this would use %rax on x86_64 */
35 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
36 return (uint64_t)hi << 32 | lo;
37 }
38 
39 int should_segv = 0;
40 
41 void sigsegv_cb(int sig)
42 {
43  if (!should_segv)
44  {
45  fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
46  exit(0);
47  }
48  if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
49  {
50  perror("prctl");
51  exit(0);
52  }
53  should_segv = 0;
54 
55  rdtsc();
56 }
57 
58 void task(void)
59 {
60  signal(SIGSEGV, sigsegv_cb);
61  alarm(10);
62  for(;;)
63  {
64  rdtsc();
65  if (should_segv)
66  {
67  fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
68  exit(0);
69  }
70  if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
71  {
72  perror("prctl");
73  exit(0);
74  }
75  should_segv = 1;
76  }
77 }
78 
79 
80 int main(int argc, char **argv)
81 {
82  int n_tasks = 100, i;
83 
84  fprintf(stderr, "[No further output means we're allright]\n");
85 
86  for (i=0; i<n_tasks; i++)
87  if (fork() == 0)
88  task();
89 
90  for (i=0; i<n_tasks; i++)
91  wait(NULL);
92 
93  exit(0);
94 }
95