runtime/interpreter/shadow_frame.h - LeafOS-Project/android_art - Gitiles

 /*
  * Copyright (C) 2011 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.
  */

 #ifndef ART_RUNTIME_INTERPRETER_SHADOW_FRAME_H_
 #define ART_RUNTIME_INTERPRETER_SHADOW_FRAME_H_

 #include <cstdint>
 #include <cstring>
 #include <string>

 #include "base/locks.h"
 #include "base/macros.h"
 #include "lock_count_data.h"
 #include "read_barrier.h"
 #include "stack_reference.h"
 #include "verify_object.h"

 namespace art {

 namespace mirror {
 class Object;
 }  // namespace mirror

 class ArtMethod;
 class ShadowFrame;
 template<class MirrorType> class ObjPtr;
 class Thread;
 union JValue;

 // Forward declaration. Just calls the destructor.
 struct ShadowFrameDeleter;
 using ShadowFrameAllocaUniquePtr = std::unique_ptr<ShadowFrame, ShadowFrameDeleter>;

 // ShadowFrame has 2 possible layouts:
 //  - interpreter - separate VRegs and reference arrays. References are in the reference array.
 //  - JNI - just VRegs, but where every VReg holds a reference.
 class ShadowFrame {
  private:
   // Used to keep track of extra state the shadowframe has.
   enum class FrameFlags : uint32_t {
     // We have been requested to notify when this frame gets popped.
     kNotifyFramePop = 1 << 0,
     // We have been asked to pop this frame off the stack as soon as possible.
     kForcePopFrame = 1 << 1,
     // We have been asked to re-execute the last instruction.
     kForceRetryInst = 1 << 2,
     // Mark that we expect the next frame to retry the last instruction (used by instrumentation and
     // debuggers to keep track of required events)
     kSkipMethodExitEvents = 1 << 3,
     // Used to suppress exception events caused by other instrumentation events.
     kSkipNextExceptionEvent = 1 << 4,
     // Used to specify if DexPCMoveEvents have to be reported. These events will
     // only be reported if the method has a breakpoint set.
     kNotifyDexPcMoveEvents = 1 << 5,
   };

  public:
   // Compute size of ShadowFrame in bytes assuming it has a reference array.
   static size_t ComputeSize(uint32_t num_vregs) {
     return sizeof(ShadowFrame) + (sizeof(uint32_t) * num_vregs) +
            (sizeof(StackReference<mirror::Object>) * num_vregs);
   }

   // Create ShadowFrame in heap for deoptimization.
   static ShadowFrame* CreateDeoptimizedFrame(uint32_t num_vregs,
                                              ArtMethod* method,
                                              uint32_t dex_pc) {
     uint8_t* memory = new uint8_t[ComputeSize(num_vregs)];
     return CreateShadowFrameImpl(num_vregs, method, dex_pc, memory);
   }

   // Delete a ShadowFrame allocated on the heap for deoptimization.
   static void DeleteDeoptimizedFrame(ShadowFrame* sf) {
     sf->~ShadowFrame();  // Explicitly destruct.
     uint8_t* memory = reinterpret_cast<uint8_t*>(sf);
     delete[] memory;
   }

   // Create a shadow frame in a fresh alloca. This needs to be in the context of the caller.
   // Inlining doesn't work, the compiler will still undo the alloca. So this needs to be a macro.
 #define CREATE_SHADOW_FRAME(num_vregs, method, dex_pc) ({                                    \
     size_t frame_size = ShadowFrame::ComputeSize(num_vregs);                                 \
     void* alloca_mem = alloca(frame_size);                                                   \
     ShadowFrameAllocaUniquePtr(                                                              \
         ShadowFrame::CreateShadowFrameImpl((num_vregs), (method), (dex_pc), (alloca_mem)));  \
     })

   ~ShadowFrame() {}

   uint32_t NumberOfVRegs() const {
     return number_of_vregs_;
   }

   uint32_t GetDexPC() const {
     return (dex_pc_ptr_ == nullptr) ? dex_pc_ : dex_pc_ptr_ - dex_instructions_;
   }

   int16_t GetCachedHotnessCountdown() const {
     return cached_hotness_countdown_;
   }

   void SetCachedHotnessCountdown(int16_t cached_hotness_countdown) {
     cached_hotness_countdown_ = cached_hotness_countdown;
   }

   int16_t GetHotnessCountdown() const {
     return hotness_countdown_;
   }

   void SetHotnessCountdown(int16_t hotness_countdown) {
     hotness_countdown_ = hotness_countdown;
   }

   void SetDexPC(uint32_t dex_pc) {
     dex_pc_ = dex_pc;
     dex_pc_ptr_ = nullptr;
   }

   ShadowFrame* GetLink() const {
     return link_;
   }

   void SetLink(ShadowFrame* frame) {
     DCHECK_NE(this, frame);
     DCHECK_EQ(link_, nullptr);
     link_ = frame;
   }

   void ClearLink() {
     link_ = nullptr;
   }

   int32_t GetVReg(size_t i) const {
     DCHECK_LT(i, NumberOfVRegs());
     const uint32_t* vreg = &vregs_[i];
     return *reinterpret_cast<const int32_t*>(vreg);
   }

   // Shorts are extended to Ints in VRegs.  Interpreter intrinsics needs them as shorts.
   int16_t GetVRegShort(size_t i) const {
     return static_cast<int16_t>(GetVReg(i));
   }

   uint32_t* GetVRegAddr(size_t i) {
     return &vregs_[i];
   }

   uint32_t* GetShadowRefAddr(size_t i) {
     DCHECK_LT(i, NumberOfVRegs());
     return &vregs_[i + NumberOfVRegs()];
   }

   const uint16_t* GetDexInstructions() const {
     return dex_instructions_;
   }

   float GetVRegFloat(size_t i) const {
     DCHECK_LT(i, NumberOfVRegs());
     // NOTE: Strict-aliasing?
     const uint32_t* vreg = &vregs_[i];
     return *reinterpret_cast<const float*>(vreg);
   }

   int64_t GetVRegLong(size_t i) const {
     DCHECK_LT(i + 1, NumberOfVRegs());
     const uint32_t* vreg = &vregs_[i];
     using unaligned_int64 __attribute__((aligned(4))) = const int64_t;
     return *reinterpret_cast<unaligned_int64*>(vreg);
   }

   double GetVRegDouble(size_t i) const {
     DCHECK_LT(i + 1, NumberOfVRegs());
     const uint32_t* vreg = &vregs_[i];
     using unaligned_double __attribute__((aligned(4))) = const double;
     return *reinterpret_cast<unaligned_double*>(vreg);
   }

   // Look up the reference given its virtual register number.
   // If this returns non-null then this does not mean the vreg is currently a reference
   // on non-moving collectors. Check that the raw reg with GetVReg is equal to this if not certain.
   template<VerifyObjectFlags kVerifyFlags = kDefaultVerifyFlags>
   mirror::Object* GetVRegReference(size_t i) const REQUIRES_SHARED(Locks::mutator_lock_) {
     DCHECK_LT(i, NumberOfVRegs());
     mirror::Object* ref;
     ref = References()[i].AsMirrorPtr();
     ReadBarrier::MaybeAssertToSpaceInvariant(ref);
     if (kVerifyFlags & kVerifyReads) {
       VerifyObject(ref);
     }
     return ref;
   }

   // Get view of vregs as range of consecutive arguments starting at i.
   uint32_t* GetVRegArgs(size_t i) {
     return &vregs_[i];
   }

   void SetVReg(size_t i, int32_t val) {
     DCHECK_LT(i, NumberOfVRegs());
     uint32_t* vreg = &vregs_[i];
     *reinterpret_cast<int32_t*>(vreg) = val;
     // This is needed for moving collectors since these can update the vreg references if they
     // happen to agree with references in the reference array.
     References()[i].Clear();
   }

   void SetVRegFloat(size_t i, float val) {
     DCHECK_LT(i, NumberOfVRegs());
     uint32_t* vreg = &vregs_[i];
     *reinterpret_cast<float*>(vreg) = val;
     // This is needed for moving collectors since these can update the vreg references if they
     // happen to agree with references in the reference array.
     References()[i].Clear();
   }

   void SetVRegLong(size_t i, int64_t val) {
     DCHECK_LT(i + 1, NumberOfVRegs());
     uint32_t* vreg = &vregs_[i];
     using unaligned_int64 __attribute__((aligned(4))) = int64_t;
     *reinterpret_cast<unaligned_int64*>(vreg) = val;
     // This is needed for moving collectors since these can update the vreg references if they
     // happen to agree with references in the reference array.
     References()[i].Clear();
     References()[i + 1].Clear();
   }

   void SetVRegDouble(size_t i, double val) {
     DCHECK_LT(i + 1, NumberOfVRegs());
     uint32_t* vreg = &vregs_[i];
     using unaligned_double __attribute__((aligned(4))) = double;
     *reinterpret_cast<unaligned_double*>(vreg) = val;
     // This is needed for moving collectors since these can update the vreg references if they
     // happen to agree with references in the reference array.
     References()[i].Clear();
     References()[i + 1].Clear();
   }

   template<VerifyObjectFlags kVerifyFlags = kDefaultVerifyFlags>
   void SetVRegReference(size_t i, ObjPtr<mirror::Object> val)
       REQUIRES_SHARED(Locks::mutator_lock_);

   void SetMethod(ArtMethod* method) REQUIRES(Locks::mutator_lock_) {
     DCHECK(method != nullptr);
     DCHECK(method_ != nullptr);
     method_ = method;
   }

   ArtMethod* GetMethod() const REQUIRES_SHARED(Locks::mutator_lock_) {
     DCHECK(method_ != nullptr);
     return method_;
   }

   mirror::Object* GetThisObject() const REQUIRES_SHARED(Locks::mutator_lock_);

   mirror::Object* GetThisObject(uint16_t num_ins) const REQUIRES_SHARED(Locks::mutator_lock_);

   bool Contains(StackReference<mirror::Object>* shadow_frame_entry_obj) const {
     return ((&References()[0] <= shadow_frame_entry_obj) &&
             (shadow_frame_entry_obj <= (&References()[NumberOfVRegs() - 1])));
   }

   LockCountData& GetLockCountData() {
     return lock_count_data_;
   }

   static constexpr size_t LockCountDataOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, lock_count_data_);
   }

   static constexpr size_t LinkOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, link_);
   }

   static constexpr size_t MethodOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, method_);
   }

   static constexpr size_t DexPCOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, dex_pc_);
   }

   static constexpr size_t NumberOfVRegsOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, number_of_vregs_);
   }

   static constexpr size_t VRegsOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, vregs_);
   }

   static constexpr size_t ResultRegisterOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, result_register_);
   }

   static constexpr size_t DexPCPtrOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, dex_pc_ptr_);
   }

   static constexpr size_t DexInstructionsOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, dex_instructions_);
   }

   static constexpr size_t CachedHotnessCountdownOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, cached_hotness_countdown_);
   }

   static constexpr size_t HotnessCountdownOffset() {
     return OFFSETOF_MEMBER(ShadowFrame, hotness_countdown_);
   }

   // Create ShadowFrame for interpreter using provided memory.
   static ShadowFrame* CreateShadowFrameImpl(uint32_t num_vregs,
                                             ArtMethod* method,
                                             uint32_t dex_pc,
                                             void* memory) {
     return new (memory) ShadowFrame(num_vregs, method, dex_pc);
   }

   const uint16_t* GetDexPCPtr() {
     return dex_pc_ptr_;
   }

   void SetDexPCPtr(uint16_t* dex_pc_ptr) {
     dex_pc_ptr_ = dex_pc_ptr;
   }

   JValue* GetResultRegister() {
     return result_register_;
   }

   bool NeedsNotifyPop() const {
     return GetFrameFlag(FrameFlags::kNotifyFramePop);
   }

   void SetNotifyPop(bool notify) {
     UpdateFrameFlag(notify, FrameFlags::kNotifyFramePop);
   }

   bool GetForcePopFrame() const {
     return GetFrameFlag(FrameFlags::kForcePopFrame);
   }

   void SetForcePopFrame(bool enable) {
     UpdateFrameFlag(enable, FrameFlags::kForcePopFrame);
   }

   bool GetForceRetryInstruction() const {
     return GetFrameFlag(FrameFlags::kForceRetryInst);
   }

   void SetForceRetryInstruction(bool enable) {
     UpdateFrameFlag(enable, FrameFlags::kForceRetryInst);
   }

   bool GetSkipMethodExitEvents() const {
     return GetFrameFlag(FrameFlags::kSkipMethodExitEvents);
   }

   void SetSkipMethodExitEvents(bool enable) {
     UpdateFrameFlag(enable, FrameFlags::kSkipMethodExitEvents);
   }

   bool GetSkipNextExceptionEvent() const {
     return GetFrameFlag(FrameFlags::kSkipNextExceptionEvent);
   }

   void SetSkipNextExceptionEvent(bool enable) {
     UpdateFrameFlag(enable, FrameFlags::kSkipNextExceptionEvent);
   }

   bool GetNotifyDexPcMoveEvents() const {
     return GetFrameFlag(FrameFlags::kNotifyDexPcMoveEvents);
   }

   void SetNotifyDexPcMoveEvents(bool enable) {
     UpdateFrameFlag(enable, FrameFlags::kNotifyDexPcMoveEvents);
   }

   void CheckConsistentVRegs() const {
     if (kIsDebugBuild) {
       // A shadow frame visible to GC requires the following rule: for a given vreg,
       // its vreg reference equivalent should be the same, or null.
       for (uint32_t i = 0; i < NumberOfVRegs(); ++i) {
         int32_t reference_value = References()[i].AsVRegValue();
         CHECK((GetVReg(i) == reference_value) || (reference_value == 0));
       }
     }
   }

  private:
   ShadowFrame(uint32_t num_vregs, ArtMethod* method, uint32_t dex_pc)
       : link_(nullptr),
         method_(method),
         result_register_(nullptr),
         dex_pc_ptr_(nullptr),
         dex_instructions_(nullptr),
         number_of_vregs_(num_vregs),
         dex_pc_(dex_pc),
         cached_hotness_countdown_(0),
         hotness_countdown_(0),
         frame_flags_(0) {
     memset(vregs_, 0, num_vregs * (sizeof(uint32_t) + sizeof(StackReference<mirror::Object>)));
   }

   void UpdateFrameFlag(bool enable, FrameFlags flag) {
     if (enable) {
       frame_flags_ |= static_cast<uint32_t>(flag);
     } else {
       frame_flags_ &= ~static_cast<uint32_t>(flag);
     }
   }

   bool GetFrameFlag(FrameFlags flag) const {
     return (frame_flags_ & static_cast<uint32_t>(flag)) != 0;
   }

   const StackReference<mirror::Object>* References() const {
     const uint32_t* vreg_end = &vregs_[NumberOfVRegs()];
     return reinterpret_cast<const StackReference<mirror::Object>*>(vreg_end);
   }

   StackReference<mirror::Object>* References() {
     return const_cast<StackReference<mirror::Object>*>(
         const_cast<const ShadowFrame*>(this)->References());
   }

   // Link to previous shadow frame or null.
   ShadowFrame* link_;
   ArtMethod* method_;
   JValue* result_register_;
   const uint16_t* dex_pc_ptr_;
   // Dex instruction base of the code item.
   const uint16_t* dex_instructions_;
   LockCountData lock_count_data_;  // This may contain GC roots when lock counting is active.
   const uint32_t number_of_vregs_;
   uint32_t dex_pc_;
   int16_t cached_hotness_countdown_;
   int16_t hotness_countdown_;

   // This is a set of ShadowFrame::FrameFlags which denote special states this frame is in.
   // NB alignment requires that this field takes 4 bytes no matter its size. Only 3 bits are
   // currently used.
   uint32_t frame_flags_;

   // This is a two-part array:
   //  - [0..number_of_vregs) holds the raw virtual registers, and each element here is always 4
   //    bytes.
   //  - [number_of_vregs..number_of_vregs*2) holds only reference registers. Each element here is
   //    ptr-sized.
   // In other words when a primitive is stored in vX, the second (reference) part of the array will
   // be null. When a reference is stored in vX, the second (reference) part of the array will be a
   // copy of vX.
   uint32_t vregs_[0];

   DISALLOW_IMPLICIT_CONSTRUCTORS(ShadowFrame);
 };

 struct ShadowFrameDeleter {
   inline void operator()(ShadowFrame* frame) {
     if (frame != nullptr) {
       frame->~ShadowFrame();
     }
   }
 };

 }  // namespace art

 #endif  // ART_RUNTIME_INTERPRETER_SHADOW_FRAME_H_
	/*
	* Copyright (C) 2011 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.
	*/

	#ifndef ART_RUNTIME_INTERPRETER_SHADOW_FRAME_H_
	#define ART_RUNTIME_INTERPRETER_SHADOW_FRAME_H_

	#include <cstdint>
	#include <cstring>
	#include <string>

	#include "base/locks.h"
	#include "base/macros.h"
	#include "lock_count_data.h"
	#include "read_barrier.h"
	#include "stack_reference.h"
	#include "verify_object.h"

	namespace art {

	namespace mirror {
	class Object;
	} // namespace mirror

	class ArtMethod;
	class ShadowFrame;
	template<class MirrorType> class ObjPtr;
	class Thread;
	union JValue;

	// Forward declaration. Just calls the destructor.
	struct ShadowFrameDeleter;
	using ShadowFrameAllocaUniquePtr = std::unique_ptr<ShadowFrame, ShadowFrameDeleter>;

	// ShadowFrame has 2 possible layouts:
	// - interpreter - separate VRegs and reference arrays. References are in the reference array.
	// - JNI - just VRegs, but where every VReg holds a reference.
	class ShadowFrame {
	private:
	// Used to keep track of extra state the shadowframe has.
	enum class FrameFlags : uint32_t {
	// We have been requested to notify when this frame gets popped.
	kNotifyFramePop = 1 << 0,
	// We have been asked to pop this frame off the stack as soon as possible.
	kForcePopFrame = 1 << 1,
	// We have been asked to re-execute the last instruction.
	kForceRetryInst = 1 << 2,
	// Mark that we expect the next frame to retry the last instruction (used by instrumentation and
	// debuggers to keep track of required events)
	kSkipMethodExitEvents = 1 << 3,
	// Used to suppress exception events caused by other instrumentation events.
	kSkipNextExceptionEvent = 1 << 4,
	// Used to specify if DexPCMoveEvents have to be reported. These events will
	// only be reported if the method has a breakpoint set.
	kNotifyDexPcMoveEvents = 1 << 5,
	};

	public:
	// Compute size of ShadowFrame in bytes assuming it has a reference array.
	static size_t ComputeSize(uint32_t num_vregs) {
	return sizeof(ShadowFrame) + (sizeof(uint32_t) * num_vregs) +
	(sizeof(StackReference<mirror::Object>) * num_vregs);
	}

	// Create ShadowFrame in heap for deoptimization.
	static ShadowFrame* CreateDeoptimizedFrame(uint32_t num_vregs,
	ArtMethod* method,
	uint32_t dex_pc) {
	uint8_t* memory = new uint8_t[ComputeSize(num_vregs)];
	return CreateShadowFrameImpl(num_vregs, method, dex_pc, memory);
	}

	// Delete a ShadowFrame allocated on the heap for deoptimization.
	static void DeleteDeoptimizedFrame(ShadowFrame* sf) {
	sf->~ShadowFrame(); // Explicitly destruct.
	uint8_t* memory = reinterpret_cast<uint8_t*>(sf);
	delete[] memory;
	}

	// Create a shadow frame in a fresh alloca. This needs to be in the context of the caller.
	// Inlining doesn't work, the compiler will still undo the alloca. So this needs to be a macro.
	#define CREATE_SHADOW_FRAME(num_vregs, method, dex_pc) ({ \
	size_t frame_size = ShadowFrame::ComputeSize(num_vregs); \
	void* alloca_mem = alloca(frame_size); \
	ShadowFrameAllocaUniquePtr( \
	ShadowFrame::CreateShadowFrameImpl((num_vregs), (method), (dex_pc), (alloca_mem))); \
	})

	~ShadowFrame() {}

	uint32_t NumberOfVRegs() const {
	return number_of_vregs_;
	}

	uint32_t GetDexPC() const {
	return (dex_pc_ptr_ == nullptr) ? dex_pc_ : dex_pc_ptr_ - dex_instructions_;
	}

	int16_t GetCachedHotnessCountdown() const {
	return cached_hotness_countdown_;
	}

	void SetCachedHotnessCountdown(int16_t cached_hotness_countdown) {
	cached_hotness_countdown_ = cached_hotness_countdown;
	}

	int16_t GetHotnessCountdown() const {
	return hotness_countdown_;
	}

	void SetHotnessCountdown(int16_t hotness_countdown) {
	hotness_countdown_ = hotness_countdown;
	}

	void SetDexPC(uint32_t dex_pc) {
	dex_pc_ = dex_pc;
	dex_pc_ptr_ = nullptr;
	}

	ShadowFrame* GetLink() const {
	return link_;
	}

	void SetLink(ShadowFrame* frame) {
	DCHECK_NE(this, frame);
	DCHECK_EQ(link_, nullptr);
	link_ = frame;
	}

	void ClearLink() {
	link_ = nullptr;
	}

	int32_t GetVReg(size_t i) const {
	DCHECK_LT(i, NumberOfVRegs());
	const uint32_t* vreg = &vregs_[i];
	return reinterpret_cast<const int32_t>(vreg);
	}

	// Shorts are extended to Ints in VRegs. Interpreter intrinsics needs them as shorts.
	int16_t GetVRegShort(size_t i) const {
	return static_cast<int16_t>(GetVReg(i));
	}

	uint32_t* GetVRegAddr(size_t i) {
	return &vregs_[i];
	}

	uint32_t* GetShadowRefAddr(size_t i) {
	DCHECK_LT(i, NumberOfVRegs());
	return &vregs_[i + NumberOfVRegs()];
	}

	const uint16_t* GetDexInstructions() const {
	return dex_instructions_;
	}

	float GetVRegFloat(size_t i) const {
	DCHECK_LT(i, NumberOfVRegs());
	// NOTE: Strict-aliasing?
	const uint32_t* vreg = &vregs_[i];
	return reinterpret_cast<const float>(vreg);
	}

	int64_t GetVRegLong(size_t i) const {
	DCHECK_LT(i + 1, NumberOfVRegs());
	const uint32_t* vreg = &vregs_[i];
	using unaligned_int64 __attribute__((aligned(4))) = const int64_t;
	return reinterpret_cast<unaligned_int64>(vreg);
	}

	double GetVRegDouble(size_t i) const {
	DCHECK_LT(i + 1, NumberOfVRegs());
	const uint32_t* vreg = &vregs_[i];
	using unaligned_double __attribute__((aligned(4))) = const double;
	return reinterpret_cast<unaligned_double>(vreg);
	}

	// Look up the reference given its virtual register number.
	// If this returns non-null then this does not mean the vreg is currently a reference
	// on non-moving collectors. Check that the raw reg with GetVReg is equal to this if not certain.
	template<VerifyObjectFlags kVerifyFlags = kDefaultVerifyFlags>
	mirror::Object* GetVRegReference(size_t i) const REQUIRES_SHARED(Locks::mutator_lock_) {
	DCHECK_LT(i, NumberOfVRegs());
	mirror::Object* ref;
	ref = References()[i].AsMirrorPtr();
	ReadBarrier::MaybeAssertToSpaceInvariant(ref);
	if (kVerifyFlags & kVerifyReads) {
	VerifyObject(ref);
	}
	return ref;
	}

	// Get view of vregs as range of consecutive arguments starting at i.
	uint32_t* GetVRegArgs(size_t i) {
	return &vregs_[i];
	}

	void SetVReg(size_t i, int32_t val) {
	DCHECK_LT(i, NumberOfVRegs());
	uint32_t* vreg = &vregs_[i];
	reinterpret_cast<int32_t>(vreg) = val;
	// This is needed for moving collectors since these can update the vreg references if they
	// happen to agree with references in the reference array.
	References()[i].Clear();
	}

	void SetVRegFloat(size_t i, float val) {
	DCHECK_LT(i, NumberOfVRegs());
	uint32_t* vreg = &vregs_[i];
	reinterpret_cast<float>(vreg) = val;
	// This is needed for moving collectors since these can update the vreg references if they
	// happen to agree with references in the reference array.
	References()[i].Clear();
	}

	void SetVRegLong(size_t i, int64_t val) {
	DCHECK_LT(i + 1, NumberOfVRegs());
	uint32_t* vreg = &vregs_[i];
	using unaligned_int64 __attribute__((aligned(4))) = int64_t;
	reinterpret_cast<unaligned_int64>(vreg) = val;
	// This is needed for moving collectors since these can update the vreg references if they
	// happen to agree with references in the reference array.
	References()[i].Clear();
	References()[i + 1].Clear();
	}

	void SetVRegDouble(size_t i, double val) {
	DCHECK_LT(i + 1, NumberOfVRegs());
	uint32_t* vreg = &vregs_[i];
	using unaligned_double __attribute__((aligned(4))) = double;
	reinterpret_cast<unaligned_double>(vreg) = val;
	// This is needed for moving collectors since these can update the vreg references if they
	// happen to agree with references in the reference array.
	References()[i].Clear();
	References()[i + 1].Clear();
	}

	template<VerifyObjectFlags kVerifyFlags = kDefaultVerifyFlags>
	void SetVRegReference(size_t i, ObjPtr<mirror::Object> val)
	REQUIRES_SHARED(Locks::mutator_lock_);

	void SetMethod(ArtMethod* method) REQUIRES(Locks::mutator_lock_) {
	DCHECK(method != nullptr);
	DCHECK(method_ != nullptr);
	method_ = method;
	}

	ArtMethod* GetMethod() const REQUIRES_SHARED(Locks::mutator_lock_) {
	DCHECK(method_ != nullptr);
	return method_;
	}

	mirror::Object* GetThisObject() const REQUIRES_SHARED(Locks::mutator_lock_);

	mirror::Object* GetThisObject(uint16_t num_ins) const REQUIRES_SHARED(Locks::mutator_lock_);

	bool Contains(StackReference<mirror::Object>* shadow_frame_entry_obj) const {
	return ((&References()[0] <= shadow_frame_entry_obj) &&
	(shadow_frame_entry_obj <= (&References()[NumberOfVRegs() - 1])));
	}

	LockCountData& GetLockCountData() {
	return lock_count_data_;
	}

	static constexpr size_t LockCountDataOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, lock_count_data_);
	}

	static constexpr size_t LinkOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, link_);
	}

	static constexpr size_t MethodOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, method_);
	}

	static constexpr size_t DexPCOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, dex_pc_);
	}

	static constexpr size_t NumberOfVRegsOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, number_of_vregs_);
	}

	static constexpr size_t VRegsOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, vregs_);
	}

	static constexpr size_t ResultRegisterOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, result_register_);
	}

	static constexpr size_t DexPCPtrOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, dex_pc_ptr_);
	}

	static constexpr size_t DexInstructionsOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, dex_instructions_);
	}

	static constexpr size_t CachedHotnessCountdownOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, cached_hotness_countdown_);
	}

	static constexpr size_t HotnessCountdownOffset() {
	return OFFSETOF_MEMBER(ShadowFrame, hotness_countdown_);
	}

	// Create ShadowFrame for interpreter using provided memory.
	static ShadowFrame* CreateShadowFrameImpl(uint32_t num_vregs,
	ArtMethod* method,
	uint32_t dex_pc,
	void* memory) {
	return new (memory) ShadowFrame(num_vregs, method, dex_pc);
	}

	const uint16_t* GetDexPCPtr() {
	return dex_pc_ptr_;
	}

	void SetDexPCPtr(uint16_t* dex_pc_ptr) {
	dex_pc_ptr_ = dex_pc_ptr;
	}

	JValue* GetResultRegister() {
	return result_register_;
	}

	bool NeedsNotifyPop() const {
	return GetFrameFlag(FrameFlags::kNotifyFramePop);
	}

	void SetNotifyPop(bool notify) {
	UpdateFrameFlag(notify, FrameFlags::kNotifyFramePop);
	}

	bool GetForcePopFrame() const {
	return GetFrameFlag(FrameFlags::kForcePopFrame);
	}

	void SetForcePopFrame(bool enable) {
	UpdateFrameFlag(enable, FrameFlags::kForcePopFrame);
	}

	bool GetForceRetryInstruction() const {
	return GetFrameFlag(FrameFlags::kForceRetryInst);
	}

	void SetForceRetryInstruction(bool enable) {
	UpdateFrameFlag(enable, FrameFlags::kForceRetryInst);
	}

	bool GetSkipMethodExitEvents() const {
	return GetFrameFlag(FrameFlags::kSkipMethodExitEvents);
	}

	void SetSkipMethodExitEvents(bool enable) {
	UpdateFrameFlag(enable, FrameFlags::kSkipMethodExitEvents);
	}

	bool GetSkipNextExceptionEvent() const {
	return GetFrameFlag(FrameFlags::kSkipNextExceptionEvent);
	}

	void SetSkipNextExceptionEvent(bool enable) {
	UpdateFrameFlag(enable, FrameFlags::kSkipNextExceptionEvent);
	}

	bool GetNotifyDexPcMoveEvents() const {
	return GetFrameFlag(FrameFlags::kNotifyDexPcMoveEvents);
	}

	void SetNotifyDexPcMoveEvents(bool enable) {
	UpdateFrameFlag(enable, FrameFlags::kNotifyDexPcMoveEvents);
	}

	void CheckConsistentVRegs() const {
	if (kIsDebugBuild) {
	// A shadow frame visible to GC requires the following rule: for a given vreg,
	// its vreg reference equivalent should be the same, or null.
	for (uint32_t i = 0; i < NumberOfVRegs(); ++i) {
	int32_t reference_value = References()[i].AsVRegValue();
	CHECK((GetVReg(i) == reference_value) \|\| (reference_value == 0));
	}
	}
	}

	private:
	ShadowFrame(uint32_t num_vregs, ArtMethod* method, uint32_t dex_pc)
	: link_(nullptr),
	method_(method),
	result_register_(nullptr),
	dex_pc_ptr_(nullptr),
	dex_instructions_(nullptr),
	number_of_vregs_(num_vregs),
	dex_pc_(dex_pc),
	cached_hotness_countdown_(0),
	hotness_countdown_(0),
	frame_flags_(0) {
	memset(vregs_, 0, num_vregs * (sizeof(uint32_t) + sizeof(StackReference<mirror::Object>)));
	}

	void UpdateFrameFlag(bool enable, FrameFlags flag) {
	if (enable) {
	frame_flags_ \|= static_cast<uint32_t>(flag);
	} else {
	frame_flags_ &= ~static_cast<uint32_t>(flag);
	}
	}

	bool GetFrameFlag(FrameFlags flag) const {
	return (frame_flags_ & static_cast<uint32_t>(flag)) != 0;
	}

	const StackReference<mirror::Object>* References() const {
	const uint32_t* vreg_end = &vregs_[NumberOfVRegs()];
	return reinterpret_cast<const StackReference<mirror::Object>*>(vreg_end);
	}

	StackReference<mirror::Object>* References() {
	return const_cast<StackReference<mirror::Object>*>(
	const_cast<const ShadowFrame*>(this)->References());
	}

	// Link to previous shadow frame or null.
	ShadowFrame* link_;
	ArtMethod* method_;
	JValue* result_register_;
	const uint16_t* dex_pc_ptr_;
	// Dex instruction base of the code item.
	const uint16_t* dex_instructions_;
	LockCountData lock_count_data_; // This may contain GC roots when lock counting is active.
	const uint32_t number_of_vregs_;
	uint32_t dex_pc_;
	int16_t cached_hotness_countdown_;
	int16_t hotness_countdown_;

	// This is a set of ShadowFrame::FrameFlags which denote special states this frame is in.
	// NB alignment requires that this field takes 4 bytes no matter its size. Only 3 bits are
	// currently used.
	uint32_t frame_flags_;

	// This is a two-part array:
	// - [0..number_of_vregs) holds the raw virtual registers, and each element here is always 4
	// bytes.
	// - [number_of_vregs..number_of_vregs*2) holds only reference registers. Each element here is
	// ptr-sized.
	// In other words when a primitive is stored in vX, the second (reference) part of the array will
	// be null. When a reference is stored in vX, the second (reference) part of the array will be a
	// copy of vX.
	uint32_t vregs_[0];

	DISALLOW_IMPLICIT_CONSTRUCTORS(ShadowFrame);
	};

	struct ShadowFrameDeleter {
	inline void operator()(ShadowFrame* frame) {
	if (frame != nullptr) {
	frame->~ShadowFrame();
	}
	}
	};

	} // namespace art

	#endif // ART_RUNTIME_INTERPRETER_SHADOW_FRAME_H_