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/* return mach_absolute_time in %edx:%eax 35 * 36 * The algorithm we use is: 37 * 38 * ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base; 39 * 40 * rnt_shift, a constant computed during initialization, is the smallest value for which: 41 * 42 * (tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD 43 * 44 * Where SLOW_TSC_THRESHOLD is about 10e9. Since most processor's tscFreq is greater 45 * than 1GHz, rnt_shift is usually 0. rnt_tsc_scale is also a 32-bit constant: 46 * 47 * rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift); 48 */ 49 50 .globl _mach_absolute_time 51_mach_absolute_time: 52 pushl %ebp 53 movl %esp,%ebp 54 pushl %esi 55 pushl %ebx 56 570: 58 movl _COMM_PAGE_NT_GENERATION,%esi /* get generation (0 if being changed) */ 59 testl %esi,%esi /* if being updated, loop until stable */ 60 jz 0b 61 62 lfence 63 rdtsc /* get TSC in %edx:%eax */ 64 lfence 65 66 subl _COMM_PAGE_NT_TSC_BASE,%eax 67 sbbl _COMM_PAGE_NT_TSC_BASE+4,%edx 68 69 /* 70 * Prior to supporting "slow" processors, xnu always set _NT_SHIFT to 32. 71 * Now it defaults to 0, unless the processor is slow. The shifts 72 * below implicitly mask the count down to 5 bits, handling either default. 73 */ 74 movl _COMM_PAGE_NT_SHIFT,%ecx 75 shldl %cl,%eax,%edx /* shift %edx left, filling in from %eax */ 76 shll %cl,%eax /* finish shifting %edx:%eax left by _COMM_PAGE_NT_SHIFT bits */ 77 78 movl _COMM_PAGE_NT_SCALE,%ecx 79 80 movl %edx,%ebx 81 mull %ecx 82 movl %ebx,%eax 83 movl %edx,%ebx 84 mull %ecx 85 addl %ebx,%eax 86 adcl $0,%edx 87 88 addl _COMM_PAGE_NT_NS_BASE,%eax 89 adcl _COMM_PAGE_NT_NS_BASE+4,%edx 90 91 cmpl _COMM_PAGE_NT_GENERATION,%esi /* have the parameters changed? */ 92 jne 0b /* yes, loop until stable */ 93 94 popl %ebx 95 popl %esi 96 popl %ebp 97 ret 98 99#elif defined(__x86_64__) 100 101/* 102 * 64-bit version _mach_absolute_time. We return the 64-bit nanotime in %rax. 103 * 104 * The algorithm we use is: 105 * 106 * ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base; 107 * 108 * rnt_shift, a constant computed during initialization, is the smallest value for which: 109 * 110 * tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD 111 * 112 * Where SLOW_TSC_THRESHOLD is about 10e9. Since most processor's tscFreqs are greater 113 * than 1GHz, rnt_shift is usually 0. rnt_tsc_scale is also a 32-bit constant: 114 * 115 * rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift); 116 * 117 */ 118 .globl _mach_absolute_time 119_mach_absolute_time: 120 pushq %rbp // set up a frame for backtraces 121 movq %rsp,%rbp 122 movq $(_COMM_PAGE_TIME_DATA_START),%rsi 1231: 124 movl _NT_GENERATION(%rsi),%r8d // get generation 125 testl %r8d,%r8d // if 0, data is being changed... 126 jz 1b // ...so loop until stable 127 lfence 128 rdtsc // edx:eax := tsc 129 lfence 130 shlq $32,%rdx // rax := ((edx << 32) | eax), ie 64-bit tsc 131 orq %rdx,%rax 132 133 /* 134 * Prior to supporting "slow" processors, xnu always set _NT_SHIFT to 32. 135 * Now it defaults to 0, unless the processor is slow. In order to maintain 136 * compatibility with both old and new versions of xnu, we mask the shift 137 * down to 0x1F, which maps the old default (32) into the new default (0). 138 */ 139 movl _NT_SHIFT(%rsi),%ecx 140 andl $0x1F,%ecx // *** remove this line once 10.9 is GM *** 141 subq _NT_TSC_BASE(%rsi), %rax // rax := (tsc - base_tsc) 142 shlq %cl,%rax // rax := (tsc - base_tsc) << NT_SHIFT 143 movl _NT_SCALE(%rsi),%ecx 144 mulq %rcx // rdx:rax := ((tsc - base_tsc)<<shift) * scale 145 shrdq $32,%rdx,%rax // divide by 2**32 146 addq _NT_NS_BASE(%rsi),%rax // (((tsc - base_tsc) * scale) >> 32) + ns_base 147 148 cmpl _NT_GENERATION(%rsi),%r8d // did the data change during computation? 149 jne 1b 150 popq %rbp 151 ret 152 153#else 154#error Unsupported architecture 155#endif 156