/* * Tests for prctl(PR_GET_TSC, ...) / prctl(PR_SET_TSC, ...) * * Tests if the control register is updated correctly * at context switches * * Warning: this test will cause a very high load for a few seconds * */ #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <signal.h> #include <inttypes.h> #include <wait.h> #include <sys/prctl.h> #include <linux/prctl.h> /* Get/set the process' ability to use the timestamp counter instruction */ #ifndef PR_GET_TSC #define PR_GET_TSC 25 #define PR_SET_TSC 26 # define PR_TSC_ENABLE 1 /* allow the use of the timestamp counter */ # define PR_TSC_SIGSEGV 2 /* throw a SIGSEGV instead of reading the TSC */ #endif uint64_t rdtsc() { uint32_t lo, hi; /* We cannot use "=A", since this would use %rax on x86_64 */ __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi)); return (uint64_t)hi << 32 | lo; } void sigsegv_expect(int sig) { /* */ } void segvtask(void) { if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0) { perror("prctl"); exit(0); } signal(SIGSEGV, sigsegv_expect); alarm(10); rdtsc(); fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n"); exit(0); } void sigsegv_fail(int sig) { fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n"); exit(0); } void rdtsctask(void) { if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0) { perror("prctl"); exit(0); } signal(SIGSEGV, sigsegv_fail); alarm(10); for(;;) rdtsc(); } int main(int argc, char **argv) { int n_tasks = 100, i; fprintf(stderr, "[No further output means we're allright]\n"); for (i=0; i<n_tasks; i++) if (fork() == 0) { if (i & 1) segvtask(); else rdtsctask(); } for (i=0; i<n_tasks; i++) wait(NULL); exit(0); }