Root/Documentation/prctl/disable-tsc-ctxt-sw-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 * at context switches
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
30uint64_t rdtsc() {
31uint32_t lo, hi;
32/* We cannot use "=A", since this would use %rax on x86_64 */
33__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
34return (uint64_t)hi << 32 | lo;
35}
36
37void sigsegv_expect(int sig)
38{
39    /* */
40}
41
42void segvtask(void)
43{
44    if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
45    {
46        perror("prctl");
47        exit(0);
48    }
49    signal(SIGSEGV, sigsegv_expect);
50    alarm(10);
51    rdtsc();
52    fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
53    exit(0);
54}
55
56
57void sigsegv_fail(int sig)
58{
59    fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
60    exit(0);
61}
62
63void rdtsctask(void)
64{
65    if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
66    {
67        perror("prctl");
68        exit(0);
69    }
70    signal(SIGSEGV, sigsegv_fail);
71    alarm(10);
72    for(;;) rdtsc();
73}
74
75
76int main(int argc, char **argv)
77{
78    int n_tasks = 100, i;
79
80    fprintf(stderr, "[No further output means we're allright]\n");
81
82    for (i=0; i<n_tasks; i++)
83        if (fork() == 0)
84        {
85            if (i & 1)
86                segvtask();
87            else
88                rdtsctask();
89        }
90
91    for (i=0; i<n_tasks; i++)
92        wait(NULL);
93
94    exit(0);
95}
96
97

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