linux/Documentation/prctl/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
  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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