Root/Documentation/prctl/disable-tsc-on-off-stress-test.c

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
32uint64_t rdtsc() {
33uint32_t lo, hi;
34/* We cannot use "=A", since this would use %rax on x86_64 */
35__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
36return (uint64_t)hi << 32 | lo;
37}
38
39int should_segv = 0;
40
41void 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
58void 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
80int 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
96

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