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