glibc/sysdeps/unix/clock_gettime.c

/* clock_gettime -- Get the current time from a POSIX clockid_t.  Unix version.
   Copyright (C) 1999-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <stdint.h>
#include <time.h>
#include <sys/time.h>
#include <libc-internal.h>
#include <ldsodefs.h>


#if HP_TIMING_AVAIL
/* Clock frequency of the processor.  We make it a 64-bit variable
   because some jokers are already playing with processors with more
   than 4GHz.  */
static hp_timing_t freq;


/* This function is defined in the thread library.  */
extern int __pthread_clock_gettime (clockid_t clock_id, hp_timing_t freq,
				    struct timespec *tp)
     __attribute__ ((__weak__));

static int
hp_timing_gettime (clockid_t clock_id, struct timespec *tp)
{
  hp_timing_t tsc;

  if (__glibc_unlikely (freq == 0))
    {
      /* This can only happen if we haven't initialized the `freq'
	 variable yet.  Do this now. We don't have to protect this
	 code against multiple execution since all of them should
	 lead to the same result.  */
      freq = __get_clockfreq ();
      if (__glibc_unlikely (freq == 0))
	/* Something went wrong.  */
	return -1;
    }

  if (clock_id != CLOCK_PROCESS_CPUTIME_ID
      && __pthread_clock_gettime != NULL)
    return __pthread_clock_gettime (clock_id, freq, tp);

  /* Get the current counter.  */
  HP_TIMING_NOW (tsc);

  /* Compute the offset since the start time of the process.  */
  tsc -= GL(dl_cpuclock_offset);

  /* Compute the seconds.  */
  tp->tv_sec = tsc / freq;

  /* And the nanoseconds.  This computation should be stable until
     we get machines with about 16GHz frequency.  */
  tp->tv_nsec = ((tsc % freq) * UINT64_C (1000000000)) / freq;

  return 0;
}
#endif


static inline int
realtime_gettime (struct timespec *tp)
{
  struct timeval tv;
  int retval = __gettimeofday (&tv, NULL);
  if (retval == 0)
    /* Convert into `timespec'.  */
    TIMEVAL_TO_TIMESPEC (&tv, tp);
  return retval;
}

#if defined __clang__ && defined __powerpc64__
/* On ppc, __clock_gettime's body eventually expands into asm code
   that does a bctrl, but clang does not recognize the need to save
   the link register, so calls loop infinitely instead of returning.
   As workaround, make a dummy function call that forces a link
   register save.  */
volatile int clock_gettime_dummy_glob;

void __attribute__((noinline)) clock_gettime_dummy ()
{
  clock_gettime_dummy_glob = 45;
}
#endif

/* Get current value of CLOCK and store it in TP.  */
int
__clock_gettime (clockid_t clock_id, struct timespec *tp)
{
  int retval = -1;

#if defined __clang__ && defined __powerpc64__
  clock_gettime_dummy ();
#endif

  switch (clock_id)
    {
#ifdef SYSDEP_GETTIME
      SYSDEP_GETTIME;
#endif

#ifndef HANDLED_REALTIME
    case CLOCK_REALTIME:
      {
	struct timeval tv;
	retval = __gettimeofday (&tv, NULL);
	if (retval == 0)
	  TIMEVAL_TO_TIMESPEC (&tv, tp);
      }
      break;
#endif

    default:
#ifdef SYSDEP_GETTIME_CPU
      SYSDEP_GETTIME_CPU (clock_id, tp);
#endif
#if HP_TIMING_AVAIL
      if ((clock_id & ((1 << CLOCK_IDFIELD_SIZE) - 1))
	  == CLOCK_THREAD_CPUTIME_ID)
	retval = hp_timing_gettime (clock_id, tp);
      else
#endif
	__set_errno (EINVAL);
      break;

#if HP_TIMING_AVAIL && !defined HANDLED_CPUTIME
    case CLOCK_PROCESS_CPUTIME_ID:
      retval = hp_timing_gettime (clock_id, tp);
      break;
#endif
    }

  return retval;
}
weak_alias (__clock_gettime, clock_gettime)
libc_hidden_def (__clock_gettime)