Source/JavaScriptCore/heap/VerifierSlotVisitor.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2021 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  * THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "config.h"
 #include "VerifierSlotVisitor.h"

 #include "BlockDirectoryInlines.h"
 #include "ConservativeRoots.h"
 #include "GCSegmentedArrayInlines.h"
 #include "HeapCell.h"
 #include "JSCInlines.h"
 #include "VM.h"
 #include "VerifierSlotVisitorInlines.h"
 #include <wtf/StackTrace.h>

 namespace JSC {

 using MarkerData = VerifierSlotVisitor::MarkerData;

 constexpr int maxMarkingStackFramesToCapture = 100;

 MarkerData::MarkerData(ReferrerToken referrer, std::unique_ptr<StackTrace>&& stack)
     : m_referrer(referrer)
     , m_stack(WTFMove(stack))
 {
 }

 VerifierSlotVisitor::MarkedBlockData::MarkedBlockData(MarkedBlock* block)
     : m_block(block)
 {
 }

 void VerifierSlotVisitor::MarkedBlockData::addMarkerData(unsigned atomNumber, MarkerData&& marker)
 {
     if (m_markers.isEmpty())
         m_markers.grow(MarkedBlock::atomsPerBlock);
     m_markers[atomNumber] = WTFMove(marker);
 }

 const MarkerData* VerifierSlotVisitor::MarkedBlockData::markerData(unsigned atomNumber) const
 {
     auto& marker = m_markers[atomNumber];
     if (marker.stack())
         return &marker;
     return nullptr;
 }

 VerifierSlotVisitor::PreciseAllocationData::PreciseAllocationData(PreciseAllocation* allocation)
     : m_allocation(allocation)
 {
 }

 const MarkerData* VerifierSlotVisitor::PreciseAllocationData::markerData() const
 {
     if (m_marker.stack())
         return &m_marker;
     return nullptr;
 }

 void VerifierSlotVisitor::PreciseAllocationData::addMarkerData(MarkerData&& marker)
 {
     m_marker = WTFMove(marker);
 }

 const MarkerData* VerifierSlotVisitor::OpaqueRootData::markerData() const
 {
     if (m_marker.stack())
         return &m_marker;
     return nullptr;
 }

 void VerifierSlotVisitor::OpaqueRootData::addMarkerData(MarkerData&& marker)
 {
     m_marker = WTFMove(marker);
 }

 VerifierSlotVisitor::VerifierSlotVisitor(Heap& heap)
     : Base(heap, "Verifier", m_opaqueRootStorage)
 {
     m_needsExtraOpaqueRootHandling = true;
 }

 VerifierSlotVisitor::~VerifierSlotVisitor()
 {
     heap()->objectSpace().forEachBlock(
         [&] (MarkedBlock::Handle* handle) {
             handle->block().setVerifierMemo(nullptr);
         });
 }

 void VerifierSlotVisitor::addParallelConstraintTask(RefPtr<SharedTask<void(AbstractSlotVisitor&)>> task)
 {
     m_constraintTasks.append(WTFMove(task));
 }

 NO_RETURN_DUE_TO_CRASH void VerifierSlotVisitor::addParallelConstraintTask(RefPtr<SharedTask<void(SlotVisitor&)>>)
 {
     RELEASE_ASSERT_NOT_REACHED();
 }

 void VerifierSlotVisitor::executeConstraintTasks()
 {
     while (!m_constraintTasks.isEmpty())
         m_constraintTasks.takeFirst()->run(*this);
 }

 void VerifierSlotVisitor::append(const ConservativeRoots& conservativeRoots)
 {
     auto appendJSCellOrAuxiliary = [&] (HeapCell* heapCell) {
         if (!heapCell)
             return;

         if (testAndSetMarked(heapCell))
             return;

         switch (heapCell->cellKind()) {
         case HeapCell::JSCell:
         case HeapCell::JSCellWithIndexingHeader: {
             JSCell* jsCell = static_cast<JSCell*>(heapCell);
             appendToMarkStack(jsCell);
             return;
         }

         case HeapCell::Auxiliary:
             return;
         }
     };

     HeapCell** roots = conservativeRoots.roots();
     size_t size = conservativeRoots.size();
     for (size_t i = 0; i < size; ++i)
         appendJSCellOrAuxiliary(roots[i]);
 }

 void VerifierSlotVisitor::appendToMarkStack(JSCell* cell)
 {
     ASSERT(!cell->isZapped());
     m_collectorStack.append(cell);
 }

 void VerifierSlotVisitor::appendUnbarriered(JSCell* cell)
 {
     if (!cell)
         return;

     if (UNLIKELY(cell->isPreciseAllocation())) {
         if (LIKELY(isMarked(cell->preciseAllocation(), cell)))
             return;
     } else {
         MarkedBlock& block = cell->markedBlock();
         if (LIKELY(isMarked(block, cell)))
             return;
     }

     appendSlow(cell);
 }

 void VerifierSlotVisitor::appendHiddenUnbarriered(JSCell* cell)
 {
     appendUnbarriered(cell);
 }

 void VerifierSlotVisitor::didAddOpaqueRoot(void* opaqueRoot)
 {
     if (!Options::verboseVerifyGC())
         return;

     std::unique_ptr<OpaqueRootData>& data = m_opaqueRootMap.add(opaqueRoot, nullptr).iterator->value;
     if (!data)
         data = makeUnique<OpaqueRootData>();
     data->addMarkerData({ referrer(), StackTrace::captureStackTrace(maxMarkingStackFramesToCapture, 1) });
 }

 void VerifierSlotVisitor::didFindOpaqueRoot(void* opaqueRoot)
 {
     RELEASE_ASSERT(m_context && m_context->isOpaqueRootContext());
     RELEASE_ASSERT(!m_context->referrer());
     m_context->setReferrer(ReferrerToken(OpaqueRoot, opaqueRoot));
 }

 void VerifierSlotVisitor::drain()
 {
     RELEASE_ASSERT(m_mutatorStack.isEmpty());

     MarkStackArray& stack = m_collectorStack;
     if (stack.isEmpty())
         return;

     stack.refill();
     while (stack.canRemoveLast())
         visitChildren(stack.removeLast());
 }

 void VerifierSlotVisitor::dump(PrintStream& out) const
 {
     RELEASE_ASSERT(m_mutatorStack.isEmpty());
     out.print("Verifier collector stack: ", m_collectorStack.size());
 }

 void VerifierSlotVisitor::dumpMarkerData(HeapCell* cell)
 {
     auto markerDataForPreciseAllocation = [&] (PreciseAllocation& allocation) -> const MarkerData* {
         auto iterator = m_preciseAllocationMap.find(&allocation);
         if (iterator == m_preciseAllocationMap.end())
             return nullptr;
         return iterator->value->markerData();
     };

     auto markerDataForMarkedBlockCell = [&] (MarkedBlock& block, HeapCell* cell) -> const MarkerData* {
         auto iterator = m_markedBlockMap.find(&block);
         if (iterator == m_markedBlockMap.end())
             return nullptr;
         unsigned atomNumber = block.atomNumber(cell);
         return iterator->value->markerData(atomNumber);
     };

     auto markerDataForOpaqueRoot = [&] (void* opaqueRoot) -> const MarkerData* {
         auto iterator = m_opaqueRootMap.find(opaqueRoot);
         if (iterator == m_opaqueRootMap.end())
             return nullptr;
         return iterator->value->markerData();
     };

     WTF::dataFile().flush();

     void* opaqueRoot = nullptr;
     do {
         const MarkerData* markerData = nullptr;

         if (cell) {
             if (isJSCellKind(cell->cellKind()))
                 dataLogLn(JSValue(static_cast<JSCell*>(cell)));

             bool isMarked = heap()->isMarked(cell);
             const char* wasOrWasNot = isMarked ? "was" : "was NOT";
             dataLogLn("In the real GC, cell ", RawPointer(cell), " ", wasOrWasNot, " marked.");

             if (cell->isPreciseAllocation())
                 markerData = markerDataForPreciseAllocation(cell->preciseAllocation());
             else
                 markerData = markerDataForMarkedBlockCell(cell->markedBlock(), cell);
             if (!markerData) {
                 dataLogLn("Marker data is not available for cell ", RawPointer(cell));
                 break;
             }
             dataLog("In the verifier GC, cell ", RawPointer(cell), " was visited");

         } else {
             RELEASE_ASSERT(opaqueRoot);

             bool containsOpaqueRoot = heap()->m_opaqueRoots.contains(opaqueRoot);
             const char* wasOrWasNot = containsOpaqueRoot ? "was" : "was NOT";
             dataLogLn("In the real GC, opaque root ", RawPointer(opaqueRoot), " ", wasOrWasNot, " added to the heap's opaque roots.");

             markerData = markerDataForOpaqueRoot(opaqueRoot);
             if (!markerData) {
                 dataLogLn("Marker data is not available for opaque root ", RawPointer(opaqueRoot));
                 break;
             }
             dataLog("In the verifier GC, opaque root ", RawPointer(opaqueRoot), " was added");
         }

         ReferrerToken referrer = markerData->referrer();
         if (auto* referrerCell = referrer.asCell()) {
             dataLogLn(" via cell ", RawPointer(referrerCell), " at:");
             cell = referrerCell;
             opaqueRoot = nullptr;
         } else if (auto* referrerOpaqueRoot = referrer.asOpaqueRoot()) {
             dataLogLn(" via opaque root ", RawPointer(referrerOpaqueRoot), " at:");
             cell = nullptr;
             opaqueRoot = referrerOpaqueRoot;
         } else {
             auto reason = referrer.asRootMarkReason();
             if (reason != RootMarkReason::None)
                 dataLogLn(" from scan of ", reason, " roots at:");
             else
                 dataLogLn(" at:");
             cell = nullptr;
             opaqueRoot = nullptr;
         }

         markerData->stack()->dump(WTF::dataFile(), "    ");
         dataLogLn();

     } while (cell || opaqueRoot);
 }

 bool VerifierSlotVisitor::isFirstVisit() const
 {
     // In the regular GC, this return value is only used to control whether
     // UnlinkedCodeBlocks will be aged (see UnlinkedCodeBlock::visitChildrenImpl()).
     // For the verifier GC pass, we should always return false because we don't
     // want to do the aging action again.
     return false;
 }

 bool VerifierSlotVisitor::isMarked(const void* rawCell) const
 {
     HeapCell* cell = bitwise_cast<HeapCell*>(rawCell);
     if (cell->isPreciseAllocation())
         return isMarked(cell->preciseAllocation(), cell);
     return isMarked(cell->markedBlock(), cell);
 }

 bool VerifierSlotVisitor::isMarked(PreciseAllocation& allocation, HeapCell*) const
 {
     return m_preciseAllocationMap.contains(&allocation);
 }

 bool VerifierSlotVisitor::isMarked(MarkedBlock& block, HeapCell* cell) const
 {
     auto entry = m_markedBlockMap.find(&block);
     if (entry == m_markedBlockMap.end())
         return false;

     auto& data = entry->value;
     unsigned atomNumber = block.atomNumber(cell);
     return data->isMarked(atomNumber);
 }

 void VerifierSlotVisitor::markAuxiliary(const void* base)
 {
     HeapCell* cell = bitwise_cast<HeapCell*>(base);

     ASSERT(cell->heap() == heap());
     testAndSetMarked(cell);
 }

 bool VerifierSlotVisitor::mutatorIsStopped() const
 {
     return true;
 }

 bool VerifierSlotVisitor::testAndSetMarked(const void* rawCell)
 {
     HeapCell* cell = bitwise_cast<HeapCell*>(rawCell);
     if (cell->isPreciseAllocation())
         return testAndSetMarked(cell->preciseAllocation());
     return testAndSetMarked(cell->markedBlock(), cell);
 }

 bool VerifierSlotVisitor::testAndSetMarked(PreciseAllocation& allocation)
 {
     std::unique_ptr<PreciseAllocationData>& data = m_preciseAllocationMap.add(&allocation, nullptr).iterator->value;
     if (!data) {
         data = makeUnique<PreciseAllocationData>(&allocation);
         if (UNLIKELY(Options::verboseVerifyGC()))
             data->addMarkerData({ referrer(), StackTrace::captureStackTrace(maxMarkingStackFramesToCapture, 2) });
         return false;
     }
     return true;
 }

 bool VerifierSlotVisitor::testAndSetMarked(MarkedBlock& block, HeapCell* cell)
 {
     MarkedBlockData* data = block.verifierMemo<MarkedBlockData*>();
     if (UNLIKELY(!data)) {
         std::unique_ptr<MarkedBlockData>& entryData = m_markedBlockMap.add(&block, nullptr).iterator->value;
         RELEASE_ASSERT(!entryData);
         entryData = makeUnique<MarkedBlockData>(&block);
         data = entryData.get();
         block.setVerifierMemo(data);
     }

     unsigned atomNumber = block.atomNumber(cell);
     bool alreadySet = data->testAndSetMarked(atomNumber);
     if (!alreadySet && UNLIKELY(Options::verboseVerifyGC()))
         data->addMarkerData(atomNumber, { referrer(), StackTrace::captureStackTrace(maxMarkingStackFramesToCapture, 2) });
     return alreadySet;
 }

 void VerifierSlotVisitor::setMarkedAndAppendToMarkStack(JSCell* cell)
 {
     if (m_suppressVerifier)
         return;
     if (testAndSetMarked(cell))
         return;
     appendToMarkStack(cell);
 }

 void VerifierSlotVisitor::visitAsConstraint(const JSCell* cell)
 {
     visitChildren(cell);
 }

 void VerifierSlotVisitor::visitChildren(const JSCell* cell)
 {
     RELEASE_ASSERT(isMarked(cell));
     cell->methodTable(vm())->visitChildren(const_cast<JSCell*>(cell), *this);
 }

 } // namespace JSC
	/*
	* Copyright (C) 2021 Apple Inc. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
	* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
	* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
	* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
	* THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "config.h"
	#include "VerifierSlotVisitor.h"

	#include "BlockDirectoryInlines.h"
	#include "ConservativeRoots.h"
	#include "GCSegmentedArrayInlines.h"
	#include "HeapCell.h"
	#include "JSCInlines.h"
	#include "VM.h"
	#include "VerifierSlotVisitorInlines.h"
	#include <wtf/StackTrace.h>

	namespace JSC {

	using MarkerData = VerifierSlotVisitor::MarkerData;

	constexpr int maxMarkingStackFramesToCapture = 100;

	MarkerData::MarkerData(ReferrerToken referrer, std::unique_ptr<StackTrace>&& stack)
	: m_referrer(referrer)
	, m_stack(WTFMove(stack))
	{
	}

	VerifierSlotVisitor::MarkedBlockData::MarkedBlockData(MarkedBlock* block)
	: m_block(block)
	{
	}

	void VerifierSlotVisitor::MarkedBlockData::addMarkerData(unsigned atomNumber, MarkerData&& marker)
	{
	if (m_markers.isEmpty())
	m_markers.grow(MarkedBlock::atomsPerBlock);
	m_markers[atomNumber] = WTFMove(marker);
	}

	const MarkerData* VerifierSlotVisitor::MarkedBlockData::markerData(unsigned atomNumber) const
	{
	auto& marker = m_markers[atomNumber];
	if (marker.stack())
	return &marker;
	return nullptr;
	}

	VerifierSlotVisitor::PreciseAllocationData::PreciseAllocationData(PreciseAllocation* allocation)
	: m_allocation(allocation)
	{
	}

	const MarkerData* VerifierSlotVisitor::PreciseAllocationData::markerData() const
	{
	if (m_marker.stack())
	return &m_marker;
	return nullptr;
	}

	void VerifierSlotVisitor::PreciseAllocationData::addMarkerData(MarkerData&& marker)
	{
	m_marker = WTFMove(marker);
	}

	const MarkerData* VerifierSlotVisitor::OpaqueRootData::markerData() const
	{
	if (m_marker.stack())
	return &m_marker;
	return nullptr;
	}

	void VerifierSlotVisitor::OpaqueRootData::addMarkerData(MarkerData&& marker)
	{
	m_marker = WTFMove(marker);
	}

	VerifierSlotVisitor::VerifierSlotVisitor(Heap& heap)
	: Base(heap, "Verifier", m_opaqueRootStorage)
	{
	m_needsExtraOpaqueRootHandling = true;
	}

	VerifierSlotVisitor::~VerifierSlotVisitor()
	{
	heap()->objectSpace().forEachBlock(
	[&] (MarkedBlock::Handle* handle) {
	handle->block().setVerifierMemo(nullptr);
	});
	}

	void VerifierSlotVisitor::addParallelConstraintTask(RefPtr<SharedTask<void(AbstractSlotVisitor&)>> task)
	{
	m_constraintTasks.append(WTFMove(task));
	}

	NO_RETURN_DUE_TO_CRASH void VerifierSlotVisitor::addParallelConstraintTask(RefPtr<SharedTask<void(SlotVisitor&)>>)
	{
	RELEASE_ASSERT_NOT_REACHED();
	}

	void VerifierSlotVisitor::executeConstraintTasks()
	{
	while (!m_constraintTasks.isEmpty())
	m_constraintTasks.takeFirst()->run(*this);
	}

	void VerifierSlotVisitor::append(const ConservativeRoots& conservativeRoots)
	{
	auto appendJSCellOrAuxiliary = [&] (HeapCell* heapCell) {
	if (!heapCell)
	return;

	if (testAndSetMarked(heapCell))
	return;

	switch (heapCell->cellKind()) {
	case HeapCell::JSCell:
	case HeapCell::JSCellWithIndexingHeader: {
	JSCell* jsCell = static_cast<JSCell*>(heapCell);
	appendToMarkStack(jsCell);
	return;
	}

	case HeapCell::Auxiliary:
	return;
	}
	};

	HeapCell** roots = conservativeRoots.roots();
	size_t size = conservativeRoots.size();
	for (size_t i = 0; i < size; ++i)
	appendJSCellOrAuxiliary(roots[i]);
	}

	void VerifierSlotVisitor::appendToMarkStack(JSCell* cell)
	{
	ASSERT(!cell->isZapped());
	m_collectorStack.append(cell);
	}

	void VerifierSlotVisitor::appendUnbarriered(JSCell* cell)
	{
	if (!cell)
	return;

	if (UNLIKELY(cell->isPreciseAllocation())) {
	if (LIKELY(isMarked(cell->preciseAllocation(), cell)))
	return;
	} else {
	MarkedBlock& block = cell->markedBlock();
	if (LIKELY(isMarked(block, cell)))
	return;
	}

	appendSlow(cell);
	}

	void VerifierSlotVisitor::appendHiddenUnbarriered(JSCell* cell)
	{
	appendUnbarriered(cell);
	}

	void VerifierSlotVisitor::didAddOpaqueRoot(void* opaqueRoot)
	{
	if (!Options::verboseVerifyGC())
	return;

	std::unique_ptr<OpaqueRootData>& data = m_opaqueRootMap.add(opaqueRoot, nullptr).iterator->value;
	if (!data)
	data = makeUnique<OpaqueRootData>();
	data->addMarkerData({ referrer(), StackTrace::captureStackTrace(maxMarkingStackFramesToCapture, 1) });
	}

	void VerifierSlotVisitor::didFindOpaqueRoot(void* opaqueRoot)
	{
	RELEASE_ASSERT(m_context && m_context->isOpaqueRootContext());
	RELEASE_ASSERT(!m_context->referrer());
	m_context->setReferrer(ReferrerToken(OpaqueRoot, opaqueRoot));
	}

	void VerifierSlotVisitor::drain()
	{
	RELEASE_ASSERT(m_mutatorStack.isEmpty());

	MarkStackArray& stack = m_collectorStack;
	if (stack.isEmpty())
	return;

	stack.refill();
	while (stack.canRemoveLast())
	visitChildren(stack.removeLast());
	}

	void VerifierSlotVisitor::dump(PrintStream& out) const
	{
	RELEASE_ASSERT(m_mutatorStack.isEmpty());
	out.print("Verifier collector stack: ", m_collectorStack.size());
	}

	void VerifierSlotVisitor::dumpMarkerData(HeapCell* cell)
	{
	auto markerDataForPreciseAllocation = [&] (PreciseAllocation& allocation) -> const MarkerData* {
	auto iterator = m_preciseAllocationMap.find(&allocation);
	if (iterator == m_preciseAllocationMap.end())
	return nullptr;
	return iterator->value->markerData();
	};

	auto markerDataForMarkedBlockCell = [&] (MarkedBlock& block, HeapCell* cell) -> const MarkerData* {
	auto iterator = m_markedBlockMap.find(&block);
	if (iterator == m_markedBlockMap.end())
	return nullptr;
	unsigned atomNumber = block.atomNumber(cell);
	return iterator->value->markerData(atomNumber);
	};

	auto markerDataForOpaqueRoot = [&] (void* opaqueRoot) -> const MarkerData* {
	auto iterator = m_opaqueRootMap.find(opaqueRoot);
	if (iterator == m_opaqueRootMap.end())
	return nullptr;
	return iterator->value->markerData();
	};

	WTF::dataFile().flush();

	void* opaqueRoot = nullptr;
	do {
	const MarkerData* markerData = nullptr;

	if (cell) {
	if (isJSCellKind(cell->cellKind()))
	dataLogLn(JSValue(static_cast<JSCell*>(cell)));

	bool isMarked = heap()->isMarked(cell);
	const char* wasOrWasNot = isMarked ? "was" : "was NOT";
	dataLogLn("In the real GC, cell ", RawPointer(cell), " ", wasOrWasNot, " marked.");

	if (cell->isPreciseAllocation())
	markerData = markerDataForPreciseAllocation(cell->preciseAllocation());
	else
	markerData = markerDataForMarkedBlockCell(cell->markedBlock(), cell);
	if (!markerData) {
	dataLogLn("Marker data is not available for cell ", RawPointer(cell));
	break;
	}
	dataLog("In the verifier GC, cell ", RawPointer(cell), " was visited");

	} else {
	RELEASE_ASSERT(opaqueRoot);

	bool containsOpaqueRoot = heap()->m_opaqueRoots.contains(opaqueRoot);
	const char* wasOrWasNot = containsOpaqueRoot ? "was" : "was NOT";
	dataLogLn("In the real GC, opaque root ", RawPointer(opaqueRoot), " ", wasOrWasNot, " added to the heap's opaque roots.");

	markerData = markerDataForOpaqueRoot(opaqueRoot);
	if (!markerData) {
	dataLogLn("Marker data is not available for opaque root ", RawPointer(opaqueRoot));
	break;
	}
	dataLog("In the verifier GC, opaque root ", RawPointer(opaqueRoot), " was added");
	}

	ReferrerToken referrer = markerData->referrer();
	if (auto* referrerCell = referrer.asCell()) {
	dataLogLn(" via cell ", RawPointer(referrerCell), " at:");
	cell = referrerCell;
	opaqueRoot = nullptr;
	} else if (auto* referrerOpaqueRoot = referrer.asOpaqueRoot()) {
	dataLogLn(" via opaque root ", RawPointer(referrerOpaqueRoot), " at:");
	cell = nullptr;
	opaqueRoot = referrerOpaqueRoot;
	} else {
	auto reason = referrer.asRootMarkReason();
	if (reason != RootMarkReason::None)
	dataLogLn(" from scan of ", reason, " roots at:");
	else
	dataLogLn(" at:");
	cell = nullptr;
	opaqueRoot = nullptr;
	}

	markerData->stack()->dump(WTF::dataFile(), " ");
	dataLogLn();

	} while (cell \|\| opaqueRoot);
	}

	bool VerifierSlotVisitor::isFirstVisit() const
	{
	// In the regular GC, this return value is only used to control whether
	// UnlinkedCodeBlocks will be aged (see UnlinkedCodeBlock::visitChildrenImpl()).
	// For the verifier GC pass, we should always return false because we don't
	// want to do the aging action again.
	return false;
	}

	bool VerifierSlotVisitor::isMarked(const void* rawCell) const
	{
	HeapCell* cell = bitwise_cast<HeapCell*>(rawCell);
	if (cell->isPreciseAllocation())
	return isMarked(cell->preciseAllocation(), cell);
	return isMarked(cell->markedBlock(), cell);
	}

	bool VerifierSlotVisitor::isMarked(PreciseAllocation& allocation, HeapCell*) const
	{
	return m_preciseAllocationMap.contains(&allocation);
	}

	bool VerifierSlotVisitor::isMarked(MarkedBlock& block, HeapCell* cell) const
	{
	auto entry = m_markedBlockMap.find(&block);
	if (entry == m_markedBlockMap.end())
	return false;

	auto& data = entry->value;
	unsigned atomNumber = block.atomNumber(cell);
	return data->isMarked(atomNumber);
	}

	void VerifierSlotVisitor::markAuxiliary(const void* base)
	{
	HeapCell* cell = bitwise_cast<HeapCell*>(base);

	ASSERT(cell->heap() == heap());
	testAndSetMarked(cell);
	}

	bool VerifierSlotVisitor::mutatorIsStopped() const
	{
	return true;
	}

	bool VerifierSlotVisitor::testAndSetMarked(const void* rawCell)
	{
	HeapCell* cell = bitwise_cast<HeapCell*>(rawCell);
	if (cell->isPreciseAllocation())
	return testAndSetMarked(cell->preciseAllocation());
	return testAndSetMarked(cell->markedBlock(), cell);
	}

	bool VerifierSlotVisitor::testAndSetMarked(PreciseAllocation& allocation)
	{
	std::unique_ptr<PreciseAllocationData>& data = m_preciseAllocationMap.add(&allocation, nullptr).iterator->value;
	if (!data) {
	data = makeUnique<PreciseAllocationData>(&allocation);
	if (UNLIKELY(Options::verboseVerifyGC()))
	data->addMarkerData({ referrer(), StackTrace::captureStackTrace(maxMarkingStackFramesToCapture, 2) });
	return false;
	}
	return true;
	}

	bool VerifierSlotVisitor::testAndSetMarked(MarkedBlock& block, HeapCell* cell)
	{
	MarkedBlockData* data = block.verifierMemo<MarkedBlockData*>();
	if (UNLIKELY(!data)) {
	std::unique_ptr<MarkedBlockData>& entryData = m_markedBlockMap.add(&block, nullptr).iterator->value;
	RELEASE_ASSERT(!entryData);
	entryData = makeUnique<MarkedBlockData>(&block);
	data = entryData.get();
	block.setVerifierMemo(data);
	}

	unsigned atomNumber = block.atomNumber(cell);
	bool alreadySet = data->testAndSetMarked(atomNumber);
	if (!alreadySet && UNLIKELY(Options::verboseVerifyGC()))
	data->addMarkerData(atomNumber, { referrer(), StackTrace::captureStackTrace(maxMarkingStackFramesToCapture, 2) });
	return alreadySet;
	}

	void VerifierSlotVisitor::setMarkedAndAppendToMarkStack(JSCell* cell)
	{
	if (m_suppressVerifier)
	return;
	if (testAndSetMarked(cell))
	return;
	appendToMarkStack(cell);
	}

	void VerifierSlotVisitor::visitAsConstraint(const JSCell* cell)
	{
	visitChildren(cell);
	}

	void VerifierSlotVisitor::visitChildren(const JSCell* cell)
	{
	RELEASE_ASSERT(isMarked(cell));
	cell->methodTable(vm())->visitChildren(const_cast<JSCell>(cell), this);
	}

	} // namespace JSC