chrome/renderer/v8_unwinder.cc - chromium/src.git - Git at Google

 // Copyright 2019 The Chromium Authors
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "chrome/renderer/v8_unwinder.h"

 #include <algorithm>
 #include <memory>
 #include <utility>

 #include "base/check_op.h"
 #include "build/build_config.h"
 #include "v8/include/v8-isolate.h"

 #if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
 // V8 requires the embedder to establish the architecture define.
 #define V8_TARGET_ARCH_ARM 1
 #include "v8/include/v8-unwinder-state.h"
 #endif

 namespace {

 class V8Module : public base::ModuleCache::Module {
  public:
   enum CodeRangeType { kEmbedded, kNonEmbedded };

   V8Module(const v8::MemoryRange& memory_range, CodeRangeType code_range_type)
       : memory_range_(memory_range), code_range_type_(code_range_type) {}

   V8Module(const V8Module&) = delete;
   V8Module& operator=(const V8Module&) = delete;

   // ModuleCache::Module
   uintptr_t GetBaseAddress() const override {
     return reinterpret_cast<uintptr_t>(memory_range_.start);
   }

   std::string GetId() const override {
     return code_range_type_ == kEmbedded
                ? V8Unwinder::kV8EmbeddedCodeRangeBuildId
                : V8Unwinder::kV8CodeRangeBuildId;
   }

   base::FilePath GetDebugBasename() const override {
     return base::FilePath().AppendASCII(code_range_type_ == kEmbedded
                                             ? "V8 Embedded Code Range"
                                             : "V8 Code Range");
   }

   size_t GetSize() const override { return memory_range_.length_in_bytes; }

   bool IsNative() const override { return false; }

  private:
   const v8::MemoryRange memory_range_;
   const CodeRangeType code_range_type_;
 };

 // Heterogeneous comparator for MemoryRanges and Modules. Compares on both
 // base address and size because the module sizes can be updated while the
 // base address remains the same.
 struct MemoryRangeModuleCompare {
   bool operator()(const v8::MemoryRange& range,
                   const base::ModuleCache::Module* module) const {
     return std::make_pair(reinterpret_cast<uintptr_t>(range.start),
                           range.length_in_bytes) <
            std::make_pair(module->GetBaseAddress(), module->GetSize());
   }

   bool operator()(const base::ModuleCache::Module* module,
                   const v8::MemoryRange& range) const {
     return std::make_pair(module->GetBaseAddress(), module->GetSize()) <
            std::make_pair(reinterpret_cast<uintptr_t>(range.start),
                           range.length_in_bytes);
   }

   bool operator()(const v8::MemoryRange& a, const v8::MemoryRange& b) const {
     return std::make_pair(a.start, a.length_in_bytes) <
            std::make_pair(b.start, b.length_in_bytes);
   }
 };

 v8::MemoryRange GetEmbeddedCodeRange(v8::Isolate* isolate) {
   v8::MemoryRange range;
   isolate->GetEmbeddedCodeRange(&range.start, &range.length_in_bytes);
   return range;
 }

 void CopyCalleeSavedRegisterFromRegisterContext(
     const base::RegisterContext& register_context,
     v8::CalleeSavedRegisters* callee_saved_registers) {
 #if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
   // ARM requires callee-saved registers to be restored:
   // https://crbug.com/v8/10799.
   DCHECK(callee_saved_registers);
   callee_saved_registers->arm_r4 =
       reinterpret_cast<void*>(register_context.arm_r4);
   callee_saved_registers->arm_r5 =
       reinterpret_cast<void*>(register_context.arm_r5);
   callee_saved_registers->arm_r6 =
       reinterpret_cast<void*>(register_context.arm_r6);
   callee_saved_registers->arm_r7 =
       reinterpret_cast<void*>(register_context.arm_r7);
   callee_saved_registers->arm_r8 =
       reinterpret_cast<void*>(register_context.arm_r8);
   callee_saved_registers->arm_r9 =
       reinterpret_cast<void*>(register_context.arm_r9);
   callee_saved_registers->arm_r10 =
       reinterpret_cast<void*>(register_context.arm_r10);
 #endif
 }

 void CopyCalleeSavedRegisterToRegisterContext(
     const v8::CalleeSavedRegisters* callee_saved_registers,
     base::RegisterContext& register_context) {
 #if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
   DCHECK(callee_saved_registers);
   register_context.arm_r4 =
       reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r4);
   register_context.arm_r5 =
       reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r5);
   register_context.arm_r6 =
       reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r6);
   register_context.arm_r7 =
       reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r7);
   register_context.arm_r8 =
       reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r8);
   register_context.arm_r9 =
       reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r9);
   register_context.arm_r10 =
       reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r10);
 #endif
 }

 }  // namespace

 V8Unwinder::V8Unwinder(v8::Isolate* isolate)
     : isolate_(isolate),
       js_entry_stubs_(isolate->GetJSEntryStubs()),
       embedded_code_range_(GetEmbeddedCodeRange(isolate)) {}

 V8Unwinder::~V8Unwinder() = default;

 void V8Unwinder::InitializeModules() {
   // This function must be called only once.
   DCHECK(modules_.empty());

   // Add a module for the embedded code range.
   std::vector<std::unique_ptr<const base::ModuleCache::Module>> new_module;
   new_module.push_back(
       std::make_unique<V8Module>(embedded_code_range_, V8Module::kEmbedded));
   modules_.insert(new_module.front().get());
   module_cache()->UpdateNonNativeModules({}, std::move(new_module));
 }

 // IMPORTANT NOTE: to avoid deadlock this function must not invoke any
 // non-reentrant code that is also invoked by the target thread. In particular,
 // no heap allocation or deallocation is permitted, including indirectly via use
 // of DCHECK/CHECK or other logging statements.
 void V8Unwinder::OnStackCapture() {
   required_code_ranges_capacity_ =
       CopyCodePages(code_ranges_.capacity(), code_ranges_.buffer());
   code_ranges_.SetSize(
       std::min(required_code_ranges_capacity_, code_ranges_.capacity()));
 }

 // Update the modules based on what was recorded in |code_ranges_|. The singular
 // embedded code range was already added in in InitializeModules(). It is
 // preserved by the algorithm below, which is why kNonEmbedded is
 // unconditionally passed when creating new modules.
 void V8Unwinder::UpdateModules() {
   MemoryRangeModuleCompare less_than;

   const auto is_embedded_code_range_module =
       [this](const base::ModuleCache::Module* module) {
         return module->GetBaseAddress() ==
                    reinterpret_cast<uintptr_t>(embedded_code_range_.start) &&
                module->GetSize() == embedded_code_range_.length_in_bytes;
       };

   std::vector<std::unique_ptr<const base::ModuleCache::Module>> new_modules;
   std::vector<const base::ModuleCache::Module*> defunct_modules;

   // Identify defunct modules and create new modules seen since the last
   // sample. Code ranges provided by V8 are in sorted order.
   v8::MemoryRange* const code_ranges_start = code_ranges_.buffer();
   v8::MemoryRange* const code_ranges_end =
       code_ranges_start + code_ranges_.size();
   CHECK(std::is_sorted(code_ranges_start, code_ranges_end, less_than));
   v8::MemoryRange* range_it = code_ranges_start;
   auto modules_it = modules_.begin();

   while (range_it != code_ranges_end && modules_it != modules_.end()) {
     if (less_than(*range_it, *modules_it)) {
       new_modules.push_back(
           std::make_unique<V8Module>(*range_it, V8Module::kNonEmbedded));
       modules_.insert(modules_it, new_modules.back().get());
       ++range_it;
     } else if (less_than(*modules_it, *range_it)) {
       // Avoid deleting the embedded code range module if it wasn't provided in
       // |code_ranges_|. This could happen if |code_ranges_| had insufficient
       // capacity when the code pages were copied.
       if (!is_embedded_code_range_module(*modules_it)) {
         defunct_modules.push_back(*modules_it);
         modules_it = modules_.erase(modules_it);
       } else {
         ++modules_it;
       }
     } else {
       // The range already has a module, so there's nothing to do.
       ++range_it;
       ++modules_it;
     }
   }

   while (range_it != code_ranges_end) {
     new_modules.push_back(
         std::make_unique<V8Module>(*range_it, V8Module::kNonEmbedded));
     modules_.insert(modules_it, new_modules.back().get());
     ++range_it;
   }

   while (modules_it != modules_.end()) {
     if (!is_embedded_code_range_module(*modules_it)) {
       defunct_modules.push_back(*modules_it);
       modules_it = modules_.erase(modules_it);
     } else {
       ++modules_it;
     }
   }

   module_cache()->UpdateNonNativeModules(defunct_modules,
                                          std::move(new_modules));
   code_ranges_.ExpandCapacityIfNecessary(required_code_ranges_capacity_);
 }

 bool V8Unwinder::CanUnwindFrom(const base::Frame& current_frame) const {
   const base::ModuleCache::Module* module = current_frame.module;
   if (!module)
     return false;
   const auto loc = modules_.find(module);
   DCHECK(loc == modules_.end() || *loc == module);
   return loc != modules_.end();
 }

 base::UnwindResult V8Unwinder::TryUnwind(base::RegisterContext* thread_context,
                                          uintptr_t stack_top,
                                          std::vector<base::Frame>* stack) {
   v8::RegisterState register_state;
   register_state.pc = reinterpret_cast<void*>(
       base::RegisterContextInstructionPointer(thread_context));
   register_state.sp = reinterpret_cast<void*>(
       base::RegisterContextStackPointer(thread_context));
   register_state.fp = reinterpret_cast<void*>(
       base::RegisterContextFramePointer(thread_context));

 #if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
   if (!register_state.callee_saved)
     register_state.callee_saved = std::make_unique<v8::CalleeSavedRegisters>();
 #endif
   CopyCalleeSavedRegisterFromRegisterContext(*thread_context,
                                              register_state.callee_saved.get());

   if (!v8::Unwinder::TryUnwindV8Frames(
           js_entry_stubs_, code_ranges_.size(), code_ranges_.buffer(),
           &register_state, reinterpret_cast<const void*>(stack_top))) {
     return base::UnwindResult::kAborted;
   }

   const uintptr_t prev_stack_pointer =
       base::RegisterContextStackPointer(thread_context);
   DCHECK_GT(reinterpret_cast<uintptr_t>(register_state.sp), prev_stack_pointer);
   DCHECK_LT(reinterpret_cast<uintptr_t>(register_state.sp), stack_top);

   base::RegisterContextInstructionPointer(thread_context) =
       reinterpret_cast<uintptr_t>(register_state.pc);
   base::RegisterContextStackPointer(thread_context) =
       reinterpret_cast<uintptr_t>(register_state.sp);
   base::RegisterContextFramePointer(thread_context) =
       reinterpret_cast<uintptr_t>(register_state.fp);

   CopyCalleeSavedRegisterToRegisterContext(register_state.callee_saved.get(),
                                            *thread_context);

   stack->emplace_back(
       base::RegisterContextInstructionPointer(thread_context),
       module_cache()->GetModuleForAddress(
           base::RegisterContextInstructionPointer(thread_context)));

   return base::UnwindResult::kUnrecognizedFrame;
 }

 size_t V8Unwinder::CopyCodePages(size_t capacity, v8::MemoryRange* code_pages) {
   return isolate_->CopyCodePages(capacity, code_pages);
 }

 // Synthetic build ids to use for V8 modules. The difference is in the digit
 // after the leading 5's.
 const char V8Unwinder::kV8EmbeddedCodeRangeBuildId[] =
     "5555555507284E1E874EFA4EB754964B999";
 const char V8Unwinder::kV8CodeRangeBuildId[] =
     "5555555517284E1E874EFA4EB754964B999";

 V8Unwinder::MemoryRanges::MemoryRanges()
     : capacity_(v8::Isolate::kMinCodePagesBufferSize),
       size_(0),
       ranges_(std::make_unique<v8::MemoryRange[]>(capacity_)) {}

 V8Unwinder::MemoryRanges::MemoryRanges::~MemoryRanges() = default;

 void V8Unwinder::MemoryRanges::SetSize(size_t size) {
   // DCHECKing size_ <= capacity_ is deferred to size() because the DCHECK may
   // heap allocate.
   size_ = size;
 }

 void V8Unwinder::MemoryRanges::ExpandCapacityIfNecessary(
     size_t required_capacity) {
   if (required_capacity > capacity_) {
     while (required_capacity > capacity_)
       capacity_ *= 2;
     auto new_ranges = std::make_unique<v8::MemoryRange[]>(capacity_);
     std::copy(buffer(), buffer() + size_, new_ranges.get());
     ranges_ = std::move(new_ranges);
   }
 }

 bool V8Unwinder::ModuleCompare::operator()(
     const base::ModuleCache::Module* a,
     const base::ModuleCache::Module* b) const {
   return std::make_pair(a->GetBaseAddress(), a->GetSize()) <
          std::make_pair(b->GetBaseAddress(), b->GetSize());
 }
	// Copyright 2019 The Chromium Authors
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "chrome/renderer/v8_unwinder.h"

	#include <algorithm>
	#include <memory>
	#include <utility>

	#include "base/check_op.h"
	#include "build/build_config.h"
	#include "v8/include/v8-isolate.h"

	#if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
	// V8 requires the embedder to establish the architecture define.
	#define V8_TARGET_ARCH_ARM 1
	#include "v8/include/v8-unwinder-state.h"
	#endif

	namespace {

	class V8Module : public base::ModuleCache::Module {
	public:
	enum CodeRangeType { kEmbedded, kNonEmbedded };

	V8Module(const v8::MemoryRange& memory_range, CodeRangeType code_range_type)
	: memory_range_(memory_range), code_range_type_(code_range_type) {}

	V8Module(const V8Module&) = delete;
	V8Module& operator=(const V8Module&) = delete;

	// ModuleCache::Module
	uintptr_t GetBaseAddress() const override {
	return reinterpret_cast<uintptr_t>(memory_range_.start);
	}

	std::string GetId() const override {
	return code_range_type_ == kEmbedded
	? V8Unwinder::kV8EmbeddedCodeRangeBuildId
	: V8Unwinder::kV8CodeRangeBuildId;
	}

	base::FilePath GetDebugBasename() const override {
	return base::FilePath().AppendASCII(code_range_type_ == kEmbedded
	? "V8 Embedded Code Range"
	: "V8 Code Range");
	}

	size_t GetSize() const override { return memory_range_.length_in_bytes; }

	bool IsNative() const override { return false; }

	private:
	const v8::MemoryRange memory_range_;
	const CodeRangeType code_range_type_;
	};

	// Heterogeneous comparator for MemoryRanges and Modules. Compares on both
	// base address and size because the module sizes can be updated while the
	// base address remains the same.
	struct MemoryRangeModuleCompare {
	bool operator()(const v8::MemoryRange& range,
	const base::ModuleCache::Module* module) const {
	return std::make_pair(reinterpret_cast<uintptr_t>(range.start),
	range.length_in_bytes) <
	std::make_pair(module->GetBaseAddress(), module->GetSize());
	}

	bool operator()(const base::ModuleCache::Module* module,
	const v8::MemoryRange& range) const {
	return std::make_pair(module->GetBaseAddress(), module->GetSize()) <
	std::make_pair(reinterpret_cast<uintptr_t>(range.start),
	range.length_in_bytes);
	}

	bool operator()(const v8::MemoryRange& a, const v8::MemoryRange& b) const {
	return std::make_pair(a.start, a.length_in_bytes) <
	std::make_pair(b.start, b.length_in_bytes);
	}
	};

	v8::MemoryRange GetEmbeddedCodeRange(v8::Isolate* isolate) {
	v8::MemoryRange range;
	isolate->GetEmbeddedCodeRange(&range.start, &range.length_in_bytes);
	return range;
	}

	void CopyCalleeSavedRegisterFromRegisterContext(
	const base::RegisterContext& register_context,
	v8::CalleeSavedRegisters* callee_saved_registers) {
	#if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
	// ARM requires callee-saved registers to be restored:
	// https://crbug.com/v8/10799.
	DCHECK(callee_saved_registers);
	callee_saved_registers->arm_r4 =
	reinterpret_cast<void*>(register_context.arm_r4);
	callee_saved_registers->arm_r5 =
	reinterpret_cast<void*>(register_context.arm_r5);
	callee_saved_registers->arm_r6 =
	reinterpret_cast<void*>(register_context.arm_r6);
	callee_saved_registers->arm_r7 =
	reinterpret_cast<void*>(register_context.arm_r7);
	callee_saved_registers->arm_r8 =
	reinterpret_cast<void*>(register_context.arm_r8);
	callee_saved_registers->arm_r9 =
	reinterpret_cast<void*>(register_context.arm_r9);
	callee_saved_registers->arm_r10 =
	reinterpret_cast<void*>(register_context.arm_r10);
	#endif
	}

	void CopyCalleeSavedRegisterToRegisterContext(
	const v8::CalleeSavedRegisters* callee_saved_registers,
	base::RegisterContext& register_context) {
	#if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
	DCHECK(callee_saved_registers);
	register_context.arm_r4 =
	reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r4);
	register_context.arm_r5 =
	reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r5);
	register_context.arm_r6 =
	reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r6);
	register_context.arm_r7 =
	reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r7);
	register_context.arm_r8 =
	reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r8);
	register_context.arm_r9 =
	reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r9);
	register_context.arm_r10 =
	reinterpret_cast<uintptr_t>(callee_saved_registers->arm_r10);
	#endif
	}

	} // namespace

	V8Unwinder::V8Unwinder(v8::Isolate* isolate)
	: isolate_(isolate),
	js_entry_stubs_(isolate->GetJSEntryStubs()),
	embedded_code_range_(GetEmbeddedCodeRange(isolate)) {}

	V8Unwinder::~V8Unwinder() = default;

	void V8Unwinder::InitializeModules() {
	// This function must be called only once.
	DCHECK(modules_.empty());

	// Add a module for the embedded code range.
	std::vector<std::unique_ptr<const base::ModuleCache::Module>> new_module;
	new_module.push_back(
	std::make_unique<V8Module>(embedded_code_range_, V8Module::kEmbedded));
	modules_.insert(new_module.front().get());
	module_cache()->UpdateNonNativeModules({}, std::move(new_module));
	}

	// IMPORTANT NOTE: to avoid deadlock this function must not invoke any
	// non-reentrant code that is also invoked by the target thread. In particular,
	// no heap allocation or deallocation is permitted, including indirectly via use
	// of DCHECK/CHECK or other logging statements.
	void V8Unwinder::OnStackCapture() {
	required_code_ranges_capacity_ =
	CopyCodePages(code_ranges_.capacity(), code_ranges_.buffer());
	code_ranges_.SetSize(
	std::min(required_code_ranges_capacity_, code_ranges_.capacity()));
	}

	// Update the modules based on what was recorded in \|code_ranges_\|. The singular
	// embedded code range was already added in in InitializeModules(). It is
	// preserved by the algorithm below, which is why kNonEmbedded is
	// unconditionally passed when creating new modules.
	void V8Unwinder::UpdateModules() {
	MemoryRangeModuleCompare less_than;

	const auto is_embedded_code_range_module =
	[this](const base::ModuleCache::Module* module) {
	return module->GetBaseAddress() ==
	reinterpret_cast<uintptr_t>(embedded_code_range_.start) &&
	module->GetSize() == embedded_code_range_.length_in_bytes;
	};

	std::vector<std::unique_ptr<const base::ModuleCache::Module>> new_modules;
	std::vector<const base::ModuleCache::Module*> defunct_modules;

	// Identify defunct modules and create new modules seen since the last
	// sample. Code ranges provided by V8 are in sorted order.
	v8::MemoryRange* const code_ranges_start = code_ranges_.buffer();
	v8::MemoryRange* const code_ranges_end =
	code_ranges_start + code_ranges_.size();
	CHECK(std::is_sorted(code_ranges_start, code_ranges_end, less_than));
	v8::MemoryRange* range_it = code_ranges_start;
	auto modules_it = modules_.begin();

	while (range_it != code_ranges_end && modules_it != modules_.end()) {
	if (less_than(range_it, modules_it)) {
	new_modules.push_back(
	std::make_unique<V8Module>(*range_it, V8Module::kNonEmbedded));
	modules_.insert(modules_it, new_modules.back().get());
	++range_it;
	} else if (less_than(modules_it, range_it)) {
	// Avoid deleting the embedded code range module if it wasn't provided in
	// \|code_ranges_\|. This could happen if \|code_ranges_\| had insufficient
	// capacity when the code pages were copied.
	if (!is_embedded_code_range_module(*modules_it)) {
	defunct_modules.push_back(*modules_it);
	modules_it = modules_.erase(modules_it);
	} else {
	++modules_it;
	}
	} else {
	// The range already has a module, so there's nothing to do.
	++range_it;
	++modules_it;
	}
	}

	while (range_it != code_ranges_end) {
	new_modules.push_back(
	std::make_unique<V8Module>(*range_it, V8Module::kNonEmbedded));
	modules_.insert(modules_it, new_modules.back().get());
	++range_it;
	}

	while (modules_it != modules_.end()) {
	if (!is_embedded_code_range_module(*modules_it)) {
	defunct_modules.push_back(*modules_it);
	modules_it = modules_.erase(modules_it);
	} else {
	++modules_it;
	}
	}

	module_cache()->UpdateNonNativeModules(defunct_modules,
	std::move(new_modules));
	code_ranges_.ExpandCapacityIfNecessary(required_code_ranges_capacity_);
	}

	bool V8Unwinder::CanUnwindFrom(const base::Frame& current_frame) const {
	const base::ModuleCache::Module* module = current_frame.module;
	if (!module)
	return false;
	const auto loc = modules_.find(module);
	DCHECK(loc == modules_.end() \|\| *loc == module);
	return loc != modules_.end();
	}

	base::UnwindResult V8Unwinder::TryUnwind(base::RegisterContext* thread_context,
	uintptr_t stack_top,
	std::vector<base::Frame>* stack) {
	v8::RegisterState register_state;
	register_state.pc = reinterpret_cast<void*>(
	base::RegisterContextInstructionPointer(thread_context));
	register_state.sp = reinterpret_cast<void*>(
	base::RegisterContextStackPointer(thread_context));
	register_state.fp = reinterpret_cast<void*>(
	base::RegisterContextFramePointer(thread_context));

	#if defined(ARCH_CPU_ARM_FAMILY) && defined(ARCH_CPU_32_BITS)
	if (!register_state.callee_saved)
	register_state.callee_saved = std::make_unique<v8::CalleeSavedRegisters>();
	#endif
	CopyCalleeSavedRegisterFromRegisterContext(*thread_context,
	register_state.callee_saved.get());

	if (!v8::Unwinder::TryUnwindV8Frames(
	js_entry_stubs_, code_ranges_.size(), code_ranges_.buffer(),
	&register_state, reinterpret_cast<const void*>(stack_top))) {
	return base::UnwindResult::kAborted;
	}

	const uintptr_t prev_stack_pointer =
	base::RegisterContextStackPointer(thread_context);
	DCHECK_GT(reinterpret_cast<uintptr_t>(register_state.sp), prev_stack_pointer);
	DCHECK_LT(reinterpret_cast<uintptr_t>(register_state.sp), stack_top);

	base::RegisterContextInstructionPointer(thread_context) =
	reinterpret_cast<uintptr_t>(register_state.pc);
	base::RegisterContextStackPointer(thread_context) =
	reinterpret_cast<uintptr_t>(register_state.sp);
	base::RegisterContextFramePointer(thread_context) =
	reinterpret_cast<uintptr_t>(register_state.fp);

	CopyCalleeSavedRegisterToRegisterContext(register_state.callee_saved.get(),
	*thread_context);

	stack->emplace_back(
	base::RegisterContextInstructionPointer(thread_context),
	module_cache()->GetModuleForAddress(
	base::RegisterContextInstructionPointer(thread_context)));

	return base::UnwindResult::kUnrecognizedFrame;
	}

	size_t V8Unwinder::CopyCodePages(size_t capacity, v8::MemoryRange* code_pages) {
	return isolate_->CopyCodePages(capacity, code_pages);
	}

	// Synthetic build ids to use for V8 modules. The difference is in the digit
	// after the leading 5's.
	const char V8Unwinder::kV8EmbeddedCodeRangeBuildId[] =
	"5555555507284E1E874EFA4EB754964B999";
	const char V8Unwinder::kV8CodeRangeBuildId[] =
	"5555555517284E1E874EFA4EB754964B999";

	V8Unwinder::MemoryRanges::MemoryRanges()
	: capacity_(v8::Isolate::kMinCodePagesBufferSize),
	size_(0),
	ranges_(std::make_unique<v8::MemoryRange[]>(capacity_)) {}

	V8Unwinder::MemoryRanges::MemoryRanges::~MemoryRanges() = default;

	void V8Unwinder::MemoryRanges::SetSize(size_t size) {
	// DCHECKing size_ <= capacity_ is deferred to size() because the DCHECK may
	// heap allocate.
	size_ = size;
	}

	void V8Unwinder::MemoryRanges::ExpandCapacityIfNecessary(
	size_t required_capacity) {
	if (required_capacity > capacity_) {
	while (required_capacity > capacity_)
	capacity_ *= 2;
	auto new_ranges = std::make_unique<v8::MemoryRange[]>(capacity_);
	std::copy(buffer(), buffer() + size_, new_ranges.get());
	ranges_ = std::move(new_ranges);
	}
	}

	bool V8Unwinder::ModuleCompare::operator()(
	const base::ModuleCache::Module* a,
	const base::ModuleCache::Module* b) const {
	return std::make_pair(a->GetBaseAddress(), a->GetSize()) <
	std::make_pair(b->GetBaseAddress(), b->GetSize());
	}