libsyscall/wrappers/mach_continuous_time.c

   1 /*
   2  * Copyright (c) 2015 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 #include <stddef.h>
  24 #include <stdbool.h>
  25 #include <sys/types.h>
  26 #include <machine/cpu_capabilities.h>
  27 #include <mach/mach_time.h>
  28
  29 __attribute__((visibility("hidden")))
  30 uint64_t
  31 _mach_continuous_time_base(void)
  32 {
  33 #if !defined(__x86_64__) && !defined(__arm64__)
  34         // Deal with the lack of 64-bit loads on arm32 (see mach_approximate_time.s)
  35         while(1) {
  36                 volatile uint64_t *base_ptr = (volatile uint64_t*)_COMM_PAGE_CONT_TIMEBASE;
  37                 uint64_t read1, read2;
  38                 read1 = *base_ptr;
  39 #if   defined(__i386__)
  40                 __asm__ volatile("lfence" ::: "memory");
  41 #else
  42 #error "unsupported arch"
  43 #endif
  44                 read2 = *base_ptr;
  45
  46                 if(__builtin_expect((read1 == read2), 1))
  47                         return read1;
  48         }
  49 #else // 64-bit
  50         return *(volatile uint64_t*)_COMM_PAGE_CONT_TIMEBASE;
  51 #endif // 64-bit
  52 }
  53
  54
  55 __attribute__((visibility("hidden")))
  56 kern_return_t
  57 _mach_continuous_time(uint64_t* absolute_time, uint64_t* cont_time)
  58 {
  59         volatile uint64_t *base_ptr = (volatile uint64_t*)_COMM_PAGE_CONT_TIMEBASE;
  60         volatile uint64_t read1, read2;
  61         volatile uint64_t absolute;
  62
  63         do {
  64         read1 = *base_ptr;
  65         absolute = mach_absolute_time();
  66                 read2 = *base_ptr;
  67         } while (__builtin_expect((read1 != read2), 0));
  68
  69         if (absolute_time) *absolute_time = absolute;
  70         if (cont_time) *cont_time = absolute + read1;
  71
  72         return KERN_SUCCESS;
  73 }
  74
  75 uint64_t
  76 mach_continuous_time(void)
  77 {
  78         uint64_t cont_time;
  79     _mach_continuous_time(NULL, &cont_time);
  80         return cont_time;
  81 }
  82
  83 uint64_t
  84 mach_continuous_approximate_time(void)
  85 {
  86     /*
  87      * No retry loop here because if we use a slightly too old timebase that's
  88      * okay, we are approximate time anyway.
  89      */
  90     volatile register uint64_t time_base = _mach_continuous_time_base();
  91     return time_base + mach_approximate_time();
  92 }