1 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 // This module gets enough CPU information to optimize the
6 // atomicops module on x86.
11 #include "base/atomicops.h"
13 // This file only makes sense with atomicops_internals_x86_gcc.h -- it
14 // depends on structs that are defined in that file. If atomicops.h
15 // doesn't sub-include that file, then we aren't needed, and shouldn't
16 // try to do anything.
17 #ifdef BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
19 // Inline cpuid instruction. In PIC compilations, %ebx contains the address
20 // of the global offset table. To avoid breaking such executables, this code
21 // must preserve that register's value across cpuid instructions.
23 #define cpuid(a, b, c, d, inp) \
24 asm("mov %%ebx, %%edi\n" \
26 "xchg %%edi, %%ebx\n" \
27 : "=a" (a), "=D" (b), "=c" (c), "=d" (d) : "a" (inp))
28 #elif defined(__x86_64__)
29 #define cpuid(a, b, c, d, inp) \
30 asm("mov %%rbx, %%rdi\n" \
32 "xchg %%rdi, %%rbx\n" \
33 : "=a" (a), "=D" (b), "=c" (c), "=d" (d) : "a" (inp))
36 #if defined(cpuid) // initialize the struct only on x86
38 // Set the flags so that code will run correctly and conservatively, so even
39 // if we haven't been initialized yet, we're probably single threaded, and our
40 // default values should hopefully be pretty safe.
41 struct AtomicOps_x86CPUFeatureStruct AtomicOps_Internalx86CPUFeatures = {
42 false, // bug can't exist before process spawns multiple threads
48 // Initialize the AtomicOps_Internalx86CPUFeatures struct.
49 void AtomicOps_Internalx86CPUFeaturesInit() {
55 // Get vendor string (issue CPUID with eax = 0)
56 cpuid(eax, ebx, ecx, edx, 0);
58 memcpy(vendor, &ebx, 4);
59 memcpy(vendor + 4, &edx, 4);
60 memcpy(vendor + 8, &ecx, 4);
63 // get feature flags in ecx/edx, and family/model in eax
64 cpuid(eax, ebx, ecx, edx, 1);
66 int family = (eax >> 8) & 0xf; // family and model fields
67 int model = (eax >> 4) & 0xf;
68 if (family == 0xf) { // use extended family and model fields
69 family += (eax >> 20) & 0xff;
70 model += ((eax >> 16) & 0xf) << 4;
73 // Opteron Rev E has a bug in which on very rare occasions a locked
74 // instruction doesn't act as a read-acquire barrier if followed by a
75 // non-locked read-modify-write instruction. Rev F has this bug in
76 // pre-release versions, but not in versions released to customers,
77 // so we test only for Rev E, which is family 15, model 32..63 inclusive.
78 if (strcmp(vendor, "AuthenticAMD") == 0 && // AMD
80 32 <= model && model <= 63) {
81 AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = true;
83 AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = false;
86 // edx bit 26 is SSE2 which we use to tell use whether we can use mfence
87 AtomicOps_Internalx86CPUFeatures.has_sse2 = ((edx >> 26) & 1);
90 class AtomicOpsx86Initializer {
92 AtomicOpsx86Initializer() {
93 AtomicOps_Internalx86CPUFeaturesInit();
97 // A global to get use initialized on startup via static initialization :/
98 AtomicOpsx86Initializer g_initer;
104 #endif // ifdef BASE_ATOMICOPS_INTERNALS_X86_GCC_H_