libsyscall/wrappers/mach_approximate_time.s

   1 /*
   2  * Copyright (c) 2003-2007 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_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. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28
  29 #include <sys/appleapiopts.h>
  30 #include <machine/cpu_capabilities.h>
  31
  32 #if   defined(__i386__)
  33
  34         .text
  35         .align  4, 0x90
  36         .globl  _mach_approximate_time
  37 _mach_approximate_time:
  38         pushl   %ebp                            // push a frame
  39         movl    %esp, %ebp
  40         cmpb    $0, _COMM_PAGE_APPROX_TIME_SUPPORTED // check commpage
  41                                                 //   "is supported" flag.
  42         je      _approx_time_not_supported      // if zero, fall through to
  43                                                 //   absolute_time
  44         // note the comment above for 32-bit ARM applies equally to 32-bit i386.
  45         .align  4, 0x90
  46 _approx_time_consistency_check:
  47         movl    _COMM_PAGE_APPROX_TIME+4, %edx  // load high
  48         movl    _COMM_PAGE_APPROX_TIME, %eax    // load low
  49         lfence                                  // avoid predictive reads that
  50                                                 //   could be invalid if
  51                                                 //   interrupted
  52         cmpl    _COMM_PAGE_APPROX_TIME+4, %edx  // load high and check if equal
  53                                                 // to the first read
  54         jne     _approx_time_consistency_check  // if not, try again.
  55         popl    %ebp
  56         ret
  57
  58 _approx_time_not_supported:
  59         popl    %ebp
  60         jmp     _mach_absolute_time
  61
  62 #endif