libsyscall/wrappers/mach_bridge_remote_time.c

   1 /*
   2  * Copyright (c) 2018 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 <sys/types.h>
  24 #include <machine/cpu_capabilities.h>
  25 #include <kern/remote_time.h>
  26 #include <mach/mach_time.h>
  27 #include "strings.h"
  28 #include <TargetConditionals.h>
  29
  30 #define BT_RESET_SENTINEL_TS  (~3ULL) /* from machine/machine_remote_time.h */
  31
  32 extern uint64_t __mach_bridge_remote_time(uint64_t local_time);
  33
  34 #if TARGET_OS_BRIDGE && defined(__arm64__)
  35 static uint64_t
  36 absolutetime_to_nanoseconds(uint64_t abs_time)
  37 {
  38         mach_timebase_info_data_t info;
  39         mach_timebase_info(&info);
  40         uint64_t time_in_ns = (uint64_t)(((double)info.numer / (double)info.denom) * abs_time);
  41
  42         return time_in_ns;
  43 }
  44
  45 uint64_t
  46 mach_bridge_remote_time(__unused uint64_t local_time)
  47 {
  48         uint64_t remote_time = 0;
  49         uint64_t local_time_ns = 0;
  50         uint64_t now = 0;
  51         struct bt_params params = {};
  52
  53         volatile struct bt_params *commpage_bt_params_p = (struct bt_params *)_COMM_PAGE_REMOTETIME_PARAMS;
  54         volatile uint64_t *base_local_ts_p = &commpage_bt_params_p->base_local_ts;
  55         volatile uint64_t *base_remote_ts_p = &commpage_bt_params_p->base_remote_ts;
  56         volatile double *rate_p = &commpage_bt_params_p->rate;
  57
  58         do {
  59                 params.base_local_ts = *base_local_ts_p;
  60                 if (*base_local_ts_p == BT_RESET_SENTINEL_TS) {
  61                         return 0;
  62                 }
  63                 /*
  64                  * This call contains an instruction barrier that ensures the second read of
  65                  * base_local_ts is not speculated above the first read of base_local_ts.
  66                  */
  67                 now = mach_absolute_time();
  68                 params.base_remote_ts = *base_remote_ts_p;
  69                 params.rate = *rate_p;
  70                 /*
  71                  * This barrier prevents the second read of base_local_ts from being reordered
  72                  * w.r.t the reads of other values in bt_params.
  73                  */
  74                 __asm__ volatile ("dmb ishld" ::: "memory");
  75         } while (params.base_local_ts && (params.base_local_ts != commpage_bt_params_p->base_local_ts));
  76
  77         if (!local_time) {
  78                 local_time = now;
  79         }
  80         local_time_ns = absolutetime_to_nanoseconds(local_time);
  81         if (local_time_ns < params.base_local_ts) {
  82                 remote_time = __mach_bridge_remote_time(local_time);
  83         } else {
  84                 remote_time = mach_bridge_compute_timestamp(local_time_ns, &params);
  85         }
  86         return remote_time;
  87 }
  88 #endif /* TARGET_OS_BRIDGE && defined(__arm64__) */