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// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// This module gets enough CPU information to optimize the
// atomicops module on x86.
#include <string.h>
#include "base/atomicops.h"
#include "base/basictypes.h"
// This file only makes sense with atomicops_internals_x86_gcc.h -- it
// depends on structs that are defined in that file. If atomicops.h
// doesn't sub-include that file, then we aren't needed, and shouldn't
// try to do anything.
#ifdef BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
// Inline cpuid instruction. In PIC compilations, %ebx contains the address
// of the global offset table. To avoid breaking such executables, this code
// must preserve that register's value across cpuid instructions.
#if defined(__i386__)
#define cpuid(a, b, c, d, inp) \
asm ("mov %%ebx, %%edi\n" \
"cpuid\n" \
"xchg %%edi, %%ebx\n" \
: "=a" (a), "=D" (b), "=c" (c), "=d" (d) : "a" (inp))
#elif defined (__x86_64__)
#define cpuid(a, b, c, d, inp) \
asm ("mov %%rbx, %%rdi\n" \
"cpuid\n" \
"xchg %%rdi, %%rbx\n" \
: "=a" (a), "=D" (b), "=c" (c), "=d" (d) : "a" (inp))
#endif
#if defined(cpuid) // initialize the struct only on x86
// Set the flags so that code will run correctly and conservatively, so even
// if we haven't been initialized yet, we're probably single threaded, and our
// default values should hopefully be pretty safe.
struct AtomicOps_x86CPUFeatureStruct AtomicOps_Internalx86CPUFeatures = {
false, // bug can't exist before process spawns multiple threads
false, // no SSE2
};
// Initialize the AtomicOps_Internalx86CPUFeatures struct.
static void AtomicOps_Internalx86CPUFeaturesInit() {
uint32 eax;
uint32 ebx;
uint32 ecx;
uint32 edx;
// Get vendor string (issue CPUID with eax = 0)
cpuid(eax, ebx, ecx, edx, 0);
char vendor[13];
memcpy(vendor, &ebx, 4);
memcpy(vendor + 4, &edx, 4);
memcpy(vendor + 8, &ecx, 4);
vendor[12] = 0;
// get feature flags in ecx/edx, and family/model in eax
cpuid(eax, ebx, ecx, edx, 1);
int family = (eax >> 8) & 0xf; // family and model fields
int model = (eax >> 4) & 0xf;
if (family == 0xf) { // use extended family and model fields
family += (eax >> 20) & 0xff;
model += ((eax >> 16) & 0xf) << 4;
}
// Opteron Rev E has a bug in which on very rare occasions a locked
// instruction doesn't act as a read-acquire barrier if followed by a
// non-locked read-modify-write instruction. Rev F has this bug in
// pre-release versions, but not in versions released to customers,
// so we test only for Rev E, which is family 15, model 32..63 inclusive.
if (strcmp(vendor, "AuthenticAMD") == 0 && // AMD
family == 15 &&
32 <= model && model <= 63) {
AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = true;
} else {
AtomicOps_Internalx86CPUFeatures.has_amd_lock_mb_bug = false;
}
// edx bit 26 is SSE2 which we use to tell use whether we can use mfence
AtomicOps_Internalx86CPUFeatures.has_sse2 = ((edx >> 26) & 1);
}
namespace {
class AtomicOpsx86Initializer {
public:
AtomicOpsx86Initializer() {
AtomicOps_Internalx86CPUFeaturesInit();
}
};
// A global to get use initialized on startup via static initialization :/
AtomicOpsx86Initializer g_initer;
} // namespace
#endif // if x86
#endif // ifdef BASE_ATOMICOPS_INTERNALS_X86_GCC_H_
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