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
63