libsyscall/wrappers/__commpage_gettimeofday.c

   1 /*
   2  * Copyright (c) 2008 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 #include <sys/time.h>
  25 #include <mach/mach_time.h>
  26 #include <machine/cpu_capabilities.h>
  27 #include <os/overflow.h>
  28 #include <kern/arithmetic_128.h>
  29
  30 int __commpage_gettimeofday(struct timeval *);
  31
  32 __attribute__((visibility("hidden")))
  33 int __commpage_gettimeofday_internal(struct timeval *tp, uint64_t *tbr_out);
  34
  35 int
  36 __commpage_gettimeofday(struct timeval *tp)
  37 {
  38         return __commpage_gettimeofday_internal(tp, NULL);
  39 }
  40
  41 int
  42 __commpage_gettimeofday_internal(struct timeval *tp, uint64_t *tbr_out)
  43 {
  44         uint64_t now, over;
  45         uint64_t delta, frac;
  46         uint64_t TimeStamp_tick;
  47         uint64_t TimeStamp_sec;
  48         uint64_t TimeStamp_frac;
  49         uint64_t Tick_scale;
  50         uint64_t Ticks_per_sec;
  51
  52         volatile uint64_t *gtod_TimeStamp_tick_p;
  53         volatile uint64_t *gtod_TimeStamp_sec_p;
  54         volatile uint64_t *gtod_TimeStamp_frac_p;
  55         volatile uint64_t *gtod_Ticks_scale_p;
  56         volatile uint64_t *gtod_Ticks_per_sec_p;
  57
  58         COMM_PAGE_SLOT_TYPE(new_commpage_timeofday_data_t) commpage_timeofday_datap =
  59             COMM_PAGE_SLOT(new_commpage_timeofday_data_t, NEWTIMEOFDAY_DATA);
  60
  61         gtod_TimeStamp_tick_p = &commpage_timeofday_datap->TimeStamp_tick;
  62         gtod_TimeStamp_sec_p = &commpage_timeofday_datap->TimeStamp_sec;
  63         gtod_TimeStamp_frac_p = &commpage_timeofday_datap->TimeStamp_frac;
  64         gtod_Ticks_scale_p = &commpage_timeofday_datap->Ticks_scale;
  65         gtod_Ticks_per_sec_p = &commpage_timeofday_datap->Ticks_per_sec;
  66
  67         do {
  68                 TimeStamp_tick = *gtod_TimeStamp_tick_p;
  69                 /*
  70                  * This call contains an instruction barrier which will ensure that the
  71                  * second read of the abs time isn't speculated above the reads of the
  72                  * other values above
  73                  */
  74                 now = mach_absolute_time();
  75                 TimeStamp_sec = *gtod_TimeStamp_sec_p;
  76                 TimeStamp_frac = *gtod_TimeStamp_frac_p;
  77                 Tick_scale = *gtod_Ticks_scale_p;
  78                 Ticks_per_sec = *gtod_Ticks_per_sec_p;
  79                 /*
  80                  * This barrier prevents the reordering of the second read of gtod_TimeStamp_tick_p
  81                  * w.r.t the values read just after mach_absolute_time is invoked.
  82                  */
  83 #if     (__ARM_ARCH__ >= 7)
  84                 __asm__ volatile ("dmb ishld" ::: "memory");
  85 #endif
  86         } while (TimeStamp_tick != *gtod_TimeStamp_tick_p);
  87
  88         if (TimeStamp_tick == 0) {
  89                 return 1;
  90         }
  91
  92         delta = now - TimeStamp_tick;
  93
  94         /* If more than one second force a syscall */
  95         if (delta >= Ticks_per_sec) {
  96                 return 1;
  97         }
  98
  99         if (TimeStamp_sec > __LONG_MAX__) {
 100                 return 1;
 101         }
 102
 103         tp->tv_sec = (__darwin_time_t)TimeStamp_sec;
 104
 105         over = multi_overflow(Tick_scale, delta);
 106         if (over) {
 107                 tp->tv_sec += over;
 108         }
 109
 110         /* Sum scale*delta to TimeStamp_frac, if it overflows increment sec */
 111         frac = TimeStamp_frac;
 112         frac += Tick_scale * delta;
 113         if (TimeStamp_frac > frac) {
 114                 tp->tv_sec++;
 115         }
 116
 117         /*
 118          * Convert frac (64 bit frac of a sec) to usec
 119          * usec = frac * USEC_PER_SEC / 2^64
 120          */
 121         tp->tv_usec = ((uint64_t)1000000 * (uint32_t)(frac >> 32)) >> 32;
 122
 123         if (tbr_out) {
 124                 *tbr_out = now;
 125         }
 126
 127         return 0;
 128 }