Based on kernel version 4.8. Page generated on 2016-10-06 23:18 EST.
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 32 static uint64_t rdtsc(void) 33 { 34 uint32_t lo, hi; 35 /* We cannot use "=A", since this would use %rax on x86_64 */ 36 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi)); 37 return (uint64_t)hi << 32 | lo; 38 } 39 40 int should_segv = 0; 41 42 static void sigsegv_cb(int sig) 43 { 44 if (!should_segv) 45 { 46 fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n"); 47 exit(0); 48 } 49 if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0) 50 { 51 perror("prctl"); 52 exit(0); 53 } 54 should_segv = 0; 55 56 rdtsc(); 57 } 58 59 static void task(void) 60 { 61 signal(SIGSEGV, sigsegv_cb); 62 alarm(10); 63 for(;;) 64 { 65 rdtsc(); 66 if (should_segv) 67 { 68 fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n"); 69 exit(0); 70 } 71 if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0) 72 { 73 perror("prctl"); 74 exit(0); 75 } 76 should_segv = 1; 77 } 78 } 79 80 81 int main(void) 82 { 83 int n_tasks = 100, i; 84 85 fprintf(stderr, "[No further output means we're allright]\n"); 86 87 for (i=0; i<n_tasks; i++) 88 if (fork() == 0) 89 task(); 90 91 for (i=0; i<n_tasks; i++) 92 wait(NULL); 93 94 exit(0); 95 }