/*
   * 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
  ");
  	exit(0);
  }
  
  
  void sigsegv_fail(int sig)
  {
  	fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled
  ");
  	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]
  ");
  
  	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);
  }