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 * at context switches 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 static uint64_t rdtsc(void) 32 { 33 uint32_t lo, hi; 34 /* We cannot use "=A", since this would use %rax on x86_64 */ 35 __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi)); 36 return (uint64_t)hi << 32 | lo; 37 } 38 39 static void sigsegv_expect(int sig) 40 { 41 /* */ 42 } 43 44 static void segvtask(void) 45 { 46 if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0) 47 { 48 perror("prctl"); 49 exit(0); 50 } 51 signal(SIGSEGV, sigsegv_expect); 52 alarm(10); 53 rdtsc(); 54 fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n"); 55 exit(0); 56 } 57 58 59 static void sigsegv_fail(int sig) 60 { 61 fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n"); 62 exit(0); 63 } 64 65 static void rdtsctask(void) 66 { 67 if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0) 68 { 69 perror("prctl"); 70 exit(0); 71 } 72 signal(SIGSEGV, sigsegv_fail); 73 alarm(10); 74 for(;;) rdtsc(); 75 } 76 77 78 int main(void) 79 { 80 int n_tasks = 100, i; 81 82 fprintf(stderr, "[No further output means we're all right]\n"); 83 84 for (i=0; i<n_tasks; i++) 85 if (fork() == 0) 86 { 87 if (i & 1) 88 segvtask(); 89 else 90 rdtsctask(); 91 } 92 93 for (i=0; i<n_tasks; i++) 94 wait(NULL); 95 96 exit(0); 97 } 98 99