root/tools/testing/selftests/prctl/disable-tsc-on-off-stress-test.c

DEFINITIONS

1. rdtsc
2. sigsegv_cb
3. task
4. main

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Tests for prctl(PR_GET_TSC, ...) / prctl(PR_SET_TSC, ...)
   4  *
   5  * Tests if the control register is updated correctly
   6  * when set with prctl()
   7  *
   8  * Warning: this test will cause a very high load for a few seconds
   9  *
  10  */
  11 
  12 #include <stdio.h>
  13 #include <stdlib.h>
  14 #include <unistd.h>
  15 #include <signal.h>
  16 #include <inttypes.h>
  17 #include <wait.h>
  18 
  19 
  20 #include <sys/prctl.h>
  21 #include <linux/prctl.h>
  22 
  23 /* Get/set the process' ability to use the timestamp counter instruction */
  24 #ifndef PR_GET_TSC
  25 #define PR_GET_TSC 25
  26 #define PR_SET_TSC 26
  27 # define PR_TSC_ENABLE          1   /* allow the use of the timestamp counter */
  28 # define PR_TSC_SIGSEGV         2   /* throw a SIGSEGV instead of reading the TSC */
  29 #endif
  30 
  31 /* snippet from wikipedia :-) */
  32 
  33 static uint64_t rdtsc(void)
  34 {
  35 uint32_t lo, hi;
  36 /* We cannot use "=A", since this would use %rax on x86_64 */
  37 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
  38 return (uint64_t)hi << 32 | lo;
  39 }
  40 
  41 int should_segv = 0;
  42 
  43 static void sigsegv_cb(int sig)
  44 {
  45         if (!should_segv)
  46         {
  47                 fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
  48                 exit(0);
  49         }
  50         if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
  51         {
  52                 perror("prctl");
  53                 exit(0);
  54         }
  55         should_segv = 0;
  56 
  57         rdtsc();
  58 }
  59 
  60 static void task(void)
  61 {
  62         signal(SIGSEGV, sigsegv_cb);
  63         alarm(10);
  64         for(;;)
  65         {
  66                 rdtsc();
  67                 if (should_segv)
  68                 {
  69                         fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
  70                         exit(0);
  71                 }
  72                 if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
  73                 {
  74                         perror("prctl");
  75                         exit(0);
  76                 }
  77                 should_segv = 1;
  78         }
  79 }
  80 
  81 
  82 int main(void)
  83 {
  84         int n_tasks = 100, i;
  85 
  86         fprintf(stderr, "[No further output means we're allright]\n");
  87 
  88         for (i=0; i<n_tasks; i++)
  89                 if (fork() == 0)
  90                         task();
  91 
  92         for (i=0; i<n_tasks; i++)
  93                 wait(NULL);
  94 
  95         exit(0);
  96 }
  97