runtime/arch/arm/instruction_set_features_arm.cc - LeafOS-Project/android_art - Gitiles

 /*
  * Copyright (C) 2014 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "instruction_set_features_arm.h"

 #if defined(ART_TARGET_ANDROID) && defined(__arm__)
 #include <asm/hwcap.h>
 #include <sys/auxv.h>
 #endif

 #include "signal.h"

 #include <fstream>

 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>

 #if defined(__arm__)
 extern "C" bool artCheckForArmSdivInstruction();
 extern "C" bool artCheckForArmv8AInstructions();
 #endif

 namespace art {

 using android::base::StringPrintf;

 ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromVariant(
     const std::string& variant, std::string* error_msg) {
   static const char* arm_variants_with_armv8a[] = {
       "cortex-a32",
       "cortex-a35",
       "cortex-a53",
       "cortex-a53.a57",
       "cortex-a53.a72",
       "cortex-a57",
       "cortex-a72",
       "cortex-a73",
       "exynos-m1",
       "denver",
       "kryo"
   };
   bool has_armv8a = FindVariantInArray(arm_variants_with_armv8a,
                                        arraysize(arm_variants_with_armv8a),
                                        variant);

   // Look for variants that have divide support.
   static const char* arm_variants_with_div[] = {
       "cortex-a7",
       "cortex-a12",
       "cortex-a15",
       "cortex-a17",
       "krait",
   };
   bool has_div = has_armv8a || FindVariantInArray(arm_variants_with_div,
                                                   arraysize(arm_variants_with_div),
                                                   variant);

   // Look for variants that have LPAE support.
   static const char* arm_variants_with_lpae[] = {
       "cortex-a7",
       "cortex-a12",
       "cortex-a15",
       "cortex-a17",
       "krait",
   };
   bool has_atomic_ldrd_strd = has_armv8a || FindVariantInArray(arm_variants_with_lpae,
                                                                arraysize(arm_variants_with_lpae),
                                                                variant);

   if (has_armv8a == false && has_div == false && has_atomic_ldrd_strd == false) {
     static const char* arm_variants_with_default_features[] = {
         "cortex-a5",
         "cortex-a8",
         "cortex-a9",
         "cortex-a9-mp",
         "default",
         "generic"
     };
     if (!FindVariantInArray(arm_variants_with_default_features,
                             arraysize(arm_variants_with_default_features),
                             variant)) {
       *error_msg = StringPrintf("Attempt to use unsupported ARM variant: %s", variant.c_str());
       return nullptr;
     } else {
       // Warn if we use the default features.
       LOG(WARNING) << "Using default instruction set features for ARM CPU variant (" << variant
           << ") using conservative defaults";
     }
   }
   return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
                                                             has_atomic_ldrd_strd,
                                                             has_armv8a));
 }

 ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromBitmap(uint32_t bitmap) {
   bool has_div = (bitmap & kDivBitfield) != 0;
   bool has_atomic_ldrd_strd = (bitmap & kAtomicLdrdStrdBitfield) != 0;
   bool has_armv8a = (bitmap & kARMv8A) != 0;
   return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
                                                             has_atomic_ldrd_strd,
                                                             has_armv8a));
 }

 ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromCppDefines() {
 // Note: This will not work for now since we still build the 32-bit as __ARCH_ARM_7A__.
 #if defined(__ARM_ARCH_8A__)
   const bool has_armv8a = true;
 #else
   const bool has_armv8a = false;
 #endif
 #if defined (__ARM_ARCH_8A__) || defined(__ARM_ARCH_EXT_IDIV__)
   const bool has_div = true;
 #else
   const bool has_div = false;
 #endif
 #if defined (__ARM_ARCH_8A__) || defined(__ARM_FEATURE_LPAE)
   const bool has_atomic_ldrd_strd = true;
 #else
   const bool has_atomic_ldrd_strd = false;
 #endif
   return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
                                                             has_atomic_ldrd_strd,
                                                             has_armv8a));
 }

 ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromCpuInfo() {
   // Look in /proc/cpuinfo for features we need.  Only use this when we can guarantee that
   // the kernel puts the appropriate feature flags in here.  Sometimes it doesn't.
   bool has_atomic_ldrd_strd = false;
   bool has_div = false;
   bool has_armv8a = false;

   std::ifstream in("/proc/cpuinfo");
   if (!in.fail()) {
     while (!in.eof()) {
       std::string line;
       std::getline(in, line);
       if (!in.eof()) {
         LOG(INFO) << "cpuinfo line: " << line;
         if (line.find("Features") != std::string::npos) {
           LOG(INFO) << "found features";
           if (line.find("idivt") != std::string::npos) {
             // We always expect both ARM and Thumb divide instructions to be available or not
             // available.
             CHECK_NE(line.find("idiva"), std::string::npos);
             has_div = true;
           }
           if (line.find("lpae") != std::string::npos) {
             has_atomic_ldrd_strd = true;
           }
         }
         if (line.find("architecture") != std::string::npos
             && line.find(": 8") != std::string::npos) {
           LOG(INFO) << "found architecture ARMv8";
           // Android is only run on A cores, so ARMv8 implies ARMv8-A.
           has_armv8a = true;
           // ARMv8 CPUs have LPAE and div support.
           has_div = true;
           has_atomic_ldrd_strd = true;
         }
       }
     }
     in.close();
   } else {
     LOG(ERROR) << "Failed to open /proc/cpuinfo";
   }
   return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
                                                             has_atomic_ldrd_strd,
                                                             has_armv8a));
 }

 ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromHwcap() {
   bool has_div = false;
   bool has_atomic_ldrd_strd = false;
   bool has_armv8a = false;

 #if defined(ART_TARGET_ANDROID) && defined(__arm__)
   uint64_t hwcaps = getauxval(AT_HWCAP);
   LOG(INFO) << "hwcaps=" << hwcaps;
   if ((hwcaps & HWCAP_IDIVT) != 0) {
     // We always expect both ARM and Thumb divide instructions to be available or not
     // available.
     CHECK_NE(hwcaps & HWCAP_IDIVA, 0U);
     has_div = true;
   }
   if ((hwcaps & HWCAP_LPAE) != 0) {
     has_atomic_ldrd_strd = true;
   }
   // TODO: Fix this once FPMISC makes it upstream.
   // For now we detect if we run on an ARMv8 CPU by looking for CRC32 and SHA1
   // (only available on ARMv8 CPUs).
   if ((hwcaps & HWCAP2_CRC32) != 0 && (hwcaps & HWCAP2_SHA1) != 0) {
     has_armv8a = true;
   }
 #endif

   return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
                                                             has_atomic_ldrd_strd,
                                                             has_armv8a));
 }

 // A signal handler called by a fault for an illegal instruction.  We record the fact in r0
 // and then increment the PC in the signal context to return to the next instruction.  We know the
 // instruction is 4 bytes long.
 static void bad_instr_handle(int signo ATTRIBUTE_UNUSED,
                             siginfo_t* si ATTRIBUTE_UNUSED,
                             void* data) {
 #if defined(__arm__)
   struct ucontext *uc = (struct ucontext *)data;
   struct sigcontext *sc = &uc->uc_mcontext;
   sc->arm_r0 = 0;     // Set R0 to #0 to signal error.
   sc->arm_pc += 4;    // Skip offending instruction.
 #else
   UNUSED(data);
 #endif
 }

 ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromAssembly() {
   // See if have a sdiv instruction.  Register a signal handler and try to execute an sdiv
   // instruction.  If we get a SIGILL then it's not supported.
   struct sigaction sa, osa;
   sa.sa_flags = SA_ONSTACK | SA_RESTART | SA_SIGINFO;
   sa.sa_sigaction = bad_instr_handle;
   sigemptyset(&sa.sa_mask);
   sigaction(SIGILL, &sa, &osa);

   bool has_div = false;
   bool has_armv8a = false;
 #if defined(__arm__)
   if (artCheckForArmSdivInstruction()) {
     has_div = true;
   }
   if (artCheckForArmv8AInstructions()) {
     has_armv8a = true;
   }
 #endif

   // Restore the signal handler.
   sigaction(SIGILL, &osa, nullptr);

   // Use compile time features to "detect" LPAE support.
   // TODO: write an assembly LPAE support test.
 #if defined(__ARM_FEATURE_LPAE)
   const bool has_atomic_ldrd_strd = true;
 #else
   const bool has_atomic_ldrd_strd = false;
 #endif
   return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
                                                             has_atomic_ldrd_strd,
                                                             has_armv8a));
 }

 bool ArmInstructionSetFeatures::Equals(const InstructionSetFeatures* other) const {
   if (InstructionSet::kArm != other->GetInstructionSet()) {
     return false;
   }
   const ArmInstructionSetFeatures* other_as_arm = other->AsArmInstructionSetFeatures();
   return has_div_ == other_as_arm->has_div_
       && has_atomic_ldrd_strd_ == other_as_arm->has_atomic_ldrd_strd_
       && has_armv8a_ == other_as_arm->has_armv8a_;
 }

 bool ArmInstructionSetFeatures::HasAtLeast(const InstructionSetFeatures* other) const {
   if (InstructionSet::kArm != other->GetInstructionSet()) {
     return false;
   }
   const ArmInstructionSetFeatures* other_as_arm = other->AsArmInstructionSetFeatures();
   return (has_div_ || !other_as_arm->has_div_)
       && (has_atomic_ldrd_strd_ || !other_as_arm->has_atomic_ldrd_strd_)
       && (has_armv8a_ || !other_as_arm->has_armv8a_);
 }

 uint32_t ArmInstructionSetFeatures::AsBitmap() const {
   return (has_div_ ? kDivBitfield : 0)
       | (has_atomic_ldrd_strd_ ? kAtomicLdrdStrdBitfield : 0)
       | (has_armv8a_ ? kARMv8A : 0);
 }

 std::string ArmInstructionSetFeatures::GetFeatureString() const {
   std::string result;
   if (has_div_) {
     result += "div";
   } else {
     result += "-div";
   }
   if (has_atomic_ldrd_strd_) {
     result += ",atomic_ldrd_strd";
   } else {
     result += ",-atomic_ldrd_strd";
   }
   if (has_armv8a_) {
     result += ",armv8a";
   } else {
     result += ",-armv8a";
   }
   return result;
 }

 std::unique_ptr<const InstructionSetFeatures>
 ArmInstructionSetFeatures::AddFeaturesFromSplitString(
     const std::vector<std::string>& features, std::string* error_msg) const {
   bool has_atomic_ldrd_strd = has_atomic_ldrd_strd_;
   bool has_div = has_div_;
   bool has_armv8a = has_armv8a_;
   for (auto i = features.begin(); i != features.end(); i++) {
     std::string feature = android::base::Trim(*i);
     if (feature == "div") {
       has_div = true;
     } else if (feature == "-div") {
       has_div = false;
     } else if (feature == "atomic_ldrd_strd") {
       has_atomic_ldrd_strd = true;
     } else if (feature == "-atomic_ldrd_strd") {
       has_atomic_ldrd_strd = false;
     } else if (feature == "armv8a") {
       has_armv8a = true;
     } else if (feature == "-armv8a") {
       has_armv8a = false;
     } else {
       *error_msg = StringPrintf("Unknown instruction set feature: '%s'", feature.c_str());
       return nullptr;
     }
   }
   return std::unique_ptr<const InstructionSetFeatures>(
       new ArmInstructionSetFeatures(has_div, has_atomic_ldrd_strd, has_armv8a));
 }

 }  // namespace art
	/*
	* Copyright (C) 2014 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "instruction_set_features_arm.h"

	#if defined(ART_TARGET_ANDROID) && defined(__arm__)
	#include <asm/hwcap.h>
	#include <sys/auxv.h>
	#endif

	#include "signal.h"

	#include <fstream>

	#include <android-base/logging.h>
	#include <android-base/stringprintf.h>
	#include <android-base/strings.h>

	#if defined(__arm__)
	extern "C" bool artCheckForArmSdivInstruction();
	extern "C" bool artCheckForArmv8AInstructions();
	#endif

	namespace art {

	using android::base::StringPrintf;

	ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromVariant(
	const std::string& variant, std::string* error_msg) {
	static const char* arm_variants_with_armv8a[] = {
	"cortex-a32",
	"cortex-a35",
	"cortex-a53",
	"cortex-a53.a57",
	"cortex-a53.a72",
	"cortex-a57",
	"cortex-a72",
	"cortex-a73",
	"exynos-m1",
	"denver",
	"kryo"
	};
	bool has_armv8a = FindVariantInArray(arm_variants_with_armv8a,
	arraysize(arm_variants_with_armv8a),
	variant);

	// Look for variants that have divide support.
	static const char* arm_variants_with_div[] = {
	"cortex-a7",
	"cortex-a12",
	"cortex-a15",
	"cortex-a17",
	"krait",
	};
	bool has_div = has_armv8a \|\| FindVariantInArray(arm_variants_with_div,
	arraysize(arm_variants_with_div),
	variant);

	// Look for variants that have LPAE support.
	static const char* arm_variants_with_lpae[] = {
	"cortex-a7",
	"cortex-a12",
	"cortex-a15",
	"cortex-a17",
	"krait",
	};
	bool has_atomic_ldrd_strd = has_armv8a \|\| FindVariantInArray(arm_variants_with_lpae,
	arraysize(arm_variants_with_lpae),
	variant);

	if (has_armv8a == false && has_div == false && has_atomic_ldrd_strd == false) {
	static const char* arm_variants_with_default_features[] = {
	"cortex-a5",
	"cortex-a8",
	"cortex-a9",
	"cortex-a9-mp",
	"default",
	"generic"
	};
	if (!FindVariantInArray(arm_variants_with_default_features,
	arraysize(arm_variants_with_default_features),
	variant)) {
	*error_msg = StringPrintf("Attempt to use unsupported ARM variant: %s", variant.c_str());
	return nullptr;
	} else {
	// Warn if we use the default features.
	LOG(WARNING) << "Using default instruction set features for ARM CPU variant (" << variant
	<< ") using conservative defaults";
	}
	}
	return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
	has_atomic_ldrd_strd,
	has_armv8a));
	}

	ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromBitmap(uint32_t bitmap) {
	bool has_div = (bitmap & kDivBitfield) != 0;
	bool has_atomic_ldrd_strd = (bitmap & kAtomicLdrdStrdBitfield) != 0;
	bool has_armv8a = (bitmap & kARMv8A) != 0;
	return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
	has_atomic_ldrd_strd,
	has_armv8a));
	}

	ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromCppDefines() {
	// Note: This will not work for now since we still build the 32-bit as __ARCH_ARM_7A__.
	#if defined(__ARM_ARCH_8A__)
	const bool has_armv8a = true;
	#else
	const bool has_armv8a = false;
	#endif
	#if defined (__ARM_ARCH_8A__) \|\| defined(__ARM_ARCH_EXT_IDIV__)
	const bool has_div = true;
	#else
	const bool has_div = false;
	#endif
	#if defined (__ARM_ARCH_8A__) \|\| defined(__ARM_FEATURE_LPAE)
	const bool has_atomic_ldrd_strd = true;
	#else
	const bool has_atomic_ldrd_strd = false;
	#endif
	return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
	has_atomic_ldrd_strd,
	has_armv8a));
	}

	ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromCpuInfo() {
	// Look in /proc/cpuinfo for features we need. Only use this when we can guarantee that
	// the kernel puts the appropriate feature flags in here. Sometimes it doesn't.
	bool has_atomic_ldrd_strd = false;
	bool has_div = false;
	bool has_armv8a = false;

	std::ifstream in("/proc/cpuinfo");
	if (!in.fail()) {
	while (!in.eof()) {
	std::string line;
	std::getline(in, line);
	if (!in.eof()) {
	LOG(INFO) << "cpuinfo line: " << line;
	if (line.find("Features") != std::string::npos) {
	LOG(INFO) << "found features";
	if (line.find("idivt") != std::string::npos) {
	// We always expect both ARM and Thumb divide instructions to be available or not
	// available.
	CHECK_NE(line.find("idiva"), std::string::npos);
	has_div = true;
	}
	if (line.find("lpae") != std::string::npos) {
	has_atomic_ldrd_strd = true;
	}
	}
	if (line.find("architecture") != std::string::npos
	&& line.find(": 8") != std::string::npos) {
	LOG(INFO) << "found architecture ARMv8";
	// Android is only run on A cores, so ARMv8 implies ARMv8-A.
	has_armv8a = true;
	// ARMv8 CPUs have LPAE and div support.
	has_div = true;
	has_atomic_ldrd_strd = true;
	}
	}
	}
	in.close();
	} else {
	LOG(ERROR) << "Failed to open /proc/cpuinfo";
	}
	return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
	has_atomic_ldrd_strd,
	has_armv8a));
	}

	ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromHwcap() {
	bool has_div = false;
	bool has_atomic_ldrd_strd = false;
	bool has_armv8a = false;

	#if defined(ART_TARGET_ANDROID) && defined(__arm__)
	uint64_t hwcaps = getauxval(AT_HWCAP);
	LOG(INFO) << "hwcaps=" << hwcaps;
	if ((hwcaps & HWCAP_IDIVT) != 0) {
	// We always expect both ARM and Thumb divide instructions to be available or not
	// available.
	CHECK_NE(hwcaps & HWCAP_IDIVA, 0U);
	has_div = true;
	}
	if ((hwcaps & HWCAP_LPAE) != 0) {
	has_atomic_ldrd_strd = true;
	}
	// TODO: Fix this once FPMISC makes it upstream.
	// For now we detect if we run on an ARMv8 CPU by looking for CRC32 and SHA1
	// (only available on ARMv8 CPUs).
	if ((hwcaps & HWCAP2_CRC32) != 0 && (hwcaps & HWCAP2_SHA1) != 0) {
	has_armv8a = true;
	}
	#endif

	return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
	has_atomic_ldrd_strd,
	has_armv8a));
	}

	// A signal handler called by a fault for an illegal instruction. We record the fact in r0
	// and then increment the PC in the signal context to return to the next instruction. We know the
	// instruction is 4 bytes long.
	static void bad_instr_handle(int signo ATTRIBUTE_UNUSED,
	siginfo_t* si ATTRIBUTE_UNUSED,
	void* data) {
	#if defined(__arm__)
	struct ucontext uc = (struct ucontext )data;
	struct sigcontext *sc = &uc->uc_mcontext;
	sc->arm_r0 = 0; // Set R0 to #0 to signal error.
	sc->arm_pc += 4; // Skip offending instruction.
	#else
	UNUSED(data);
	#endif
	}

	ArmFeaturesUniquePtr ArmInstructionSetFeatures::FromAssembly() {
	// See if have a sdiv instruction. Register a signal handler and try to execute an sdiv
	// instruction. If we get a SIGILL then it's not supported.
	struct sigaction sa, osa;
	sa.sa_flags = SA_ONSTACK \| SA_RESTART \| SA_SIGINFO;
	sa.sa_sigaction = bad_instr_handle;
	sigemptyset(&sa.sa_mask);
	sigaction(SIGILL, &sa, &osa);

	bool has_div = false;
	bool has_armv8a = false;
	#if defined(__arm__)
	if (artCheckForArmSdivInstruction()) {
	has_div = true;
	}
	if (artCheckForArmv8AInstructions()) {
	has_armv8a = true;
	}
	#endif

	// Restore the signal handler.
	sigaction(SIGILL, &osa, nullptr);

	// Use compile time features to "detect" LPAE support.
	// TODO: write an assembly LPAE support test.
	#if defined(__ARM_FEATURE_LPAE)
	const bool has_atomic_ldrd_strd = true;
	#else
	const bool has_atomic_ldrd_strd = false;
	#endif
	return ArmFeaturesUniquePtr(new ArmInstructionSetFeatures(has_div,
	has_atomic_ldrd_strd,
	has_armv8a));
	}

	bool ArmInstructionSetFeatures::Equals(const InstructionSetFeatures* other) const {
	if (InstructionSet::kArm != other->GetInstructionSet()) {
	return false;
	}
	const ArmInstructionSetFeatures* other_as_arm = other->AsArmInstructionSetFeatures();
	return has_div_ == other_as_arm->has_div_
	&& has_atomic_ldrd_strd_ == other_as_arm->has_atomic_ldrd_strd_
	&& has_armv8a_ == other_as_arm->has_armv8a_;
	}

	bool ArmInstructionSetFeatures::HasAtLeast(const InstructionSetFeatures* other) const {
	if (InstructionSet::kArm != other->GetInstructionSet()) {
	return false;
	}
	const ArmInstructionSetFeatures* other_as_arm = other->AsArmInstructionSetFeatures();
	return (has_div_ \|\| !other_as_arm->has_div_)
	&& (has_atomic_ldrd_strd_ \|\| !other_as_arm->has_atomic_ldrd_strd_)
	&& (has_armv8a_ \|\| !other_as_arm->has_armv8a_);
	}

	uint32_t ArmInstructionSetFeatures::AsBitmap() const {
	return (has_div_ ? kDivBitfield : 0)
	\| (has_atomic_ldrd_strd_ ? kAtomicLdrdStrdBitfield : 0)
	\| (has_armv8a_ ? kARMv8A : 0);
	}

	std::string ArmInstructionSetFeatures::GetFeatureString() const {
	std::string result;
	if (has_div_) {
	result += "div";
	} else {
	result += "-div";
	}
	if (has_atomic_ldrd_strd_) {
	result += ",atomic_ldrd_strd";
	} else {
	result += ",-atomic_ldrd_strd";
	}
	if (has_armv8a_) {
	result += ",armv8a";
	} else {
	result += ",-armv8a";
	}
	return result;
	}

	std::unique_ptr<const InstructionSetFeatures>
	ArmInstructionSetFeatures::AddFeaturesFromSplitString(
	const std::vector<std::string>& features, std::string* error_msg) const {
	bool has_atomic_ldrd_strd = has_atomic_ldrd_strd_;
	bool has_div = has_div_;
	bool has_armv8a = has_armv8a_;
	for (auto i = features.begin(); i != features.end(); i++) {
	std::string feature = android::base::Trim(*i);
	if (feature == "div") {
	has_div = true;
	} else if (feature == "-div") {
	has_div = false;
	} else if (feature == "atomic_ldrd_strd") {
	has_atomic_ldrd_strd = true;
	} else if (feature == "-atomic_ldrd_strd") {
	has_atomic_ldrd_strd = false;
	} else if (feature == "armv8a") {
	has_armv8a = true;
	} else if (feature == "-armv8a") {
	has_armv8a = false;
	} else {
	*error_msg = StringPrintf("Unknown instruction set feature: '%s'", feature.c_str());
	return nullptr;
	}
	}
	return std::unique_ptr<const InstructionSetFeatures>(
	new ArmInstructionSetFeatures(has_div, has_atomic_ldrd_strd, has_armv8a));
	}

	} // namespace art