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Marking.cpp
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Marking.cpp
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "gc/Marking-inl.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/IntegerRange.h"
#include "mozilla/ReentrancyGuard.h"
#include "mozilla/ScopeExit.h"
#include "mozilla/Unused.h"
#include <algorithm>
#include <type_traits>
#include "jsfriendapi.h"
#include "builtin/ModuleObject.h"
#include "debugger/DebugAPI.h"
#include "gc/GCInternals.h"
#include "gc/Policy.h"
#include "jit/IonCode.h"
#include "js/GCTypeMacros.h" // JS_FOR_EACH_PUBLIC_{,TAGGED_}GC_POINTER_TYPE
#include "js/SliceBudget.h"
#include "util/DiagnosticAssertions.h"
#include "util/Memory.h"
#include "util/Poison.h"
#include "vm/ArgumentsObject.h"
#include "vm/ArrayObject.h"
#include "vm/BigIntType.h"
#include "vm/EnvironmentObject.h"
#include "vm/GeneratorObject.h"
#include "vm/RegExpShared.h"
#include "vm/Scope.h"
#include "vm/Shape.h"
#include "vm/SymbolType.h"
#include "vm/TypedArrayObject.h"
#include "wasm/WasmJS.h"
#include "gc/GC-inl.h"
#include "gc/Nursery-inl.h"
#include "gc/PrivateIterators-inl.h"
#include "gc/WeakMap-inl.h"
#include "gc/Zone-inl.h"
#include "vm/GeckoProfiler-inl.h"
#include "vm/NativeObject-inl.h"
#include "vm/Realm-inl.h"
#include "vm/StringType-inl.h"
using namespace js;
using namespace js::gc;
using JS::MapTypeToTraceKind;
using mozilla::DebugOnly;
using mozilla::IntegerRange;
using mozilla::PodCopy;
// [SMDOC] GC Tracing
//
// Tracing Overview
// ================
//
// Tracing, in this context, refers to an abstract visitation of some or all of
// the GC-controlled heap. The effect of tracing an edge of the graph depends
// on the subclass of the JSTracer on whose behalf we are tracing.
//
// Marking
// -------
//
// The primary JSTracer is the GCMarker. The marking tracer causes the target
// of each traversed edge to be marked black and the target edge's children to
// be marked either gray (in the gc algorithm sense) or immediately black.
//
// Callback
// --------
//
// The secondary JSTracer is the CallbackTracer. This simply invokes a callback
// on each edge in a child.
//
// The following is a rough outline of the general struture of the tracing
// internals.
//
/* clang-format off */
// //
// .---------. .---------. .--------------------------. .----------. //
// |TraceEdge| |TraceRoot| |TraceManuallyBarrieredEdge| ... |TraceRange| ... etc. //
// '---------' '---------' '--------------------------' '----------' //
// \ \ / / //
// \ \ .-----------------. / / //
// o------------->o-|TraceEdgeInternal|-o<----------------------o //
// '-----------------' //
// / \ //
// / \ //
// .---------. .----------. .-----------------. //
// |DoMarking| |DoCallback|-------> |<JSTraceCallback>|-----------> //
// '---------' '----------' '-----------------' //
// | //
// | //
// .-----------. //
// o------------->|traverse(T)| . //
// /_\ '-----------' ' . //
// | . . ' . //
// | . . ' . //
// | . . ' . //
// | .--------------. .--------------. ' . .-----------------------. //
// | |markAndScan(T)| |markAndPush(T)| ' - |markAndTraceChildren(T)| //
// | '--------------' '--------------' '-----------------------' //
// | | \ | //
// | | \ | //
// | .----------------------. .----------------. .------------------. //
// | |eagerlyMarkChildren(T)| |pushMarkStackTop|<===Oo |T::traceChildren()|--> //
// | '----------------------' '----------------' || '------------------' //
// | | || || //
// | | || || //
// | | || || //
// o<-----------------o<========================OO============Oo //
// //
// //
// Legend: //
// ------ Direct calls //
// . . . Static dispatch //
// ====== Dispatch through a manual stack. //
// //
/* clang-format on */
/*** Tracing Invariants *****************************************************/
#if defined(DEBUG)
template <typename T>
static inline bool IsThingPoisoned(T* thing) {
const uint8_t poisonBytes[] = {
JS_FRESH_NURSERY_PATTERN, JS_SWEPT_NURSERY_PATTERN,
JS_ALLOCATED_NURSERY_PATTERN, JS_FRESH_TENURED_PATTERN,
JS_MOVED_TENURED_PATTERN, JS_SWEPT_TENURED_PATTERN,
JS_ALLOCATED_TENURED_PATTERN, JS_FREED_HEAP_PTR_PATTERN,
JS_FREED_CHUNK_PATTERN, JS_FREED_ARENA_PATTERN,
JS_SWEPT_TI_PATTERN, JS_SWEPT_CODE_PATTERN,
JS_RESET_VALUE_PATTERN, JS_POISONED_JSSCRIPT_DATA_PATTERN,
JS_OOB_PARSE_NODE_PATTERN, JS_LIFO_UNDEFINED_PATTERN,
JS_LIFO_UNINITIALIZED_PATTERN,
};
const int numPoisonBytes = sizeof(poisonBytes) / sizeof(poisonBytes[0]);
uint32_t* p =
reinterpret_cast<uint32_t*>(reinterpret_cast<FreeSpan*>(thing) + 1);
// Note: all free patterns are odd to make the common, not-poisoned case a
// single test.
if ((*p & 1) == 0) {
return false;
}
for (int i = 0; i < numPoisonBytes; ++i) {
const uint8_t pb = poisonBytes[i];
const uint32_t pw = pb | (pb << 8) | (pb << 16) | (pb << 24);
if (*p == pw) {
return true;
}
}
return false;
}
bool js::IsTracerKind(JSTracer* trc, JS::CallbackTracer::TracerKind kind) {
return trc->isCallbackTracer() &&
trc->asCallbackTracer()->getTracerKind() == kind;
}
#endif
bool ThingIsPermanentAtomOrWellKnownSymbol(JSString* str) {
return str->isPermanentAtom();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(JSLinearString* str) {
return str->isPermanentAtom();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(JSAtom* atom) {
return atom->isPermanent();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(PropertyName* name) {
return name->isPermanent();
}
bool ThingIsPermanentAtomOrWellKnownSymbol(JS::Symbol* sym) {
return sym->isWellKnownSymbol();
}
template <typename T>
static inline bool IsOwnedByOtherRuntime(JSRuntime* rt, T thing) {
bool other = thing->runtimeFromAnyThread() != rt;
MOZ_ASSERT_IF(other, ThingIsPermanentAtomOrWellKnownSymbol(thing) ||
thing->zoneFromAnyThread()->isSelfHostingZone());
return other;
}
template <typename T>
void js::CheckTracedThing(JSTracer* trc, T* thing) {
#ifdef DEBUG
MOZ_ASSERT(trc);
MOZ_ASSERT(thing);
if (!trc->checkEdges()) {
return;
}
if (IsForwarded(thing)) {
MOZ_ASSERT(IsTracerKind(trc, JS::CallbackTracer::TracerKind::Moving) ||
trc->isTenuringTracer());
thing = Forwarded(thing);
}
/* This function uses data that's not available in the nursery. */
if (IsInsideNursery(thing)) {
return;
}
/*
* Permanent atoms and things in the self-hosting zone are not associated
* with this runtime, but will be ignored during marking.
*/
if (IsOwnedByOtherRuntime(trc->runtime(), thing)) {
return;
}
Zone* zone = thing->zoneFromAnyThread();
JSRuntime* rt = trc->runtime();
MOZ_ASSERT(zone->runtimeFromAnyThread() == rt);
bool isGcMarkingTracer = trc->isMarkingTracer();
bool isUnmarkGrayTracer =
IsTracerKind(trc, JS::CallbackTracer::TracerKind::UnmarkGray);
bool isClearEdgesTracer =
IsTracerKind(trc, JS::CallbackTracer::TracerKind::ClearEdges);
if (TlsContext.get()->isMainThreadContext()) {
// If we're on the main thread we must have access to the runtime and zone.
MOZ_ASSERT(CurrentThreadCanAccessRuntime(rt));
MOZ_ASSERT(CurrentThreadCanAccessZone(zone));
} else {
MOZ_ASSERT(
isGcMarkingTracer || isUnmarkGrayTracer || isClearEdgesTracer ||
IsTracerKind(trc, JS::CallbackTracer::TracerKind::Moving) ||
IsTracerKind(trc, JS::CallbackTracer::TracerKind::GrayBuffering) ||
IsTracerKind(trc, JS::CallbackTracer::TracerKind::Sweeping));
MOZ_ASSERT_IF(!isClearEdgesTracer, CurrentThreadIsPerformingGC());
}
// It shouldn't be possible to trace into zones used by helper threads, except
// for use of ClearEdgesTracer by GCManagedDeletePolicy on a helper thread.
MOZ_ASSERT_IF(!isClearEdgesTracer, !zone->usedByHelperThread());
MOZ_ASSERT(thing->isAligned());
MOZ_ASSERT(MapTypeToTraceKind<std::remove_pointer_t<T>>::kind ==
thing->getTraceKind());
if (isGcMarkingTracer) {
GCMarker* gcMarker = GCMarker::fromTracer(trc);
MOZ_ASSERT(zone->shouldMarkInZone());
MOZ_ASSERT_IF(gcMarker->shouldCheckCompartments(),
zone->isCollectingFromAnyThread() || zone->isAtomsZone());
MOZ_ASSERT_IF(gcMarker->markColor() == MarkColor::Gray,
!zone->isGCMarkingBlackOnly() || zone->isAtomsZone());
MOZ_ASSERT(!(zone->isGCSweeping() || zone->isGCFinished() ||
zone->isGCCompacting()));
// Check that we don't stray from the current compartment and zone without
// using TraceCrossCompartmentEdge.
Compartment* comp = thing->maybeCompartment();
MOZ_ASSERT_IF(gcMarker->tracingCompartment && comp,
gcMarker->tracingCompartment == comp);
MOZ_ASSERT_IF(gcMarker->tracingZone,
gcMarker->tracingZone == zone || zone->isAtomsZone());
}
/*
* Try to assert that the thing is allocated.
*
* We would like to assert that the thing is not in the free list, but this
* check is very slow. Instead we check whether the thing has been poisoned:
* if it has not then we assume it is allocated, but if it has then it is
* either free or uninitialized in which case we check the free list.
*
* Further complications are that background sweeping may be running and
* concurrently modifiying the free list and that tracing is done off
* thread during compacting GC and reading the contents of the thing by
* IsThingPoisoned would be racy in this case.
*/
MOZ_ASSERT_IF(JS::RuntimeHeapIsBusy() && !zone->isGCSweeping() &&
!zone->isGCFinished() && !zone->isGCCompacting(),
!IsThingPoisoned(thing) ||
!InFreeList(thing->asTenured().arena(), thing));
#endif
}
template <typename T>
void js::CheckTracedThing(JSTracer* trc, T thing) {
ApplyGCThingTyped(thing, [](auto t) { CheckTracedThing(t); });
}
namespace js {
#define IMPL_CHECK_TRACED_THING(_, type, _1, _2) \
template void CheckTracedThing<type>(JSTracer*, type*);
JS_FOR_EACH_TRACEKIND(IMPL_CHECK_TRACED_THING);
#undef IMPL_CHECK_TRACED_THING
} // namespace js
static inline bool ShouldMarkCrossCompartment(GCMarker* marker, JSObject* src,
Cell* dstCell) {
MarkColor color = marker->markColor();
if (!dstCell->isTenured()) {
MOZ_ASSERT(color == MarkColor::Black);
return false;
}
TenuredCell& dst = dstCell->asTenured();
JS::Zone* dstZone = dst.zone();
if (!src->zone()->isGCMarking() && !dstZone->isGCMarking()) {
return false;
}
if (color == MarkColor::Black) {
// Check our sweep groups are correct: we should never have to
// mark something in a zone that we have started sweeping.
MOZ_ASSERT_IF(!dst.isMarkedBlack(), !dstZone->isGCSweeping());
/*
* Having black->gray edges violates our promise to the cycle collector so
* we ensure that gray things we encounter when marking black end up getting
* marked black.
*
* This can happen for two reasons:
*
* 1) If we're collecting a compartment and it has an edge to an uncollected
* compartment it's possible that the source and destination of the
* cross-compartment edge should be gray, but the source was marked black by
* the write barrier.
*
* 2) If we yield during gray marking and the write barrier marks a gray
* thing black.
*
* We handle the first case before returning whereas the second case happens
* as part of normal marking.
*/
if (dst.isMarkedGray() && !dstZone->isGCMarking()) {
UnmarkGrayGCThingUnchecked(marker->runtime(),
JS::GCCellPtr(&dst, dst.getTraceKind()));
return false;
}
return dstZone->isGCMarking();
} else {
// Check our sweep groups are correct as above.
MOZ_ASSERT_IF(!dst.isMarkedAny(), !dstZone->isGCSweeping());
if (dstZone->isGCMarkingBlackOnly()) {
/*
* The destination compartment is being not being marked gray now,
* but it will be later, so record the cell so it can be marked gray
* at the appropriate time.
*/
if (!dst.isMarkedAny()) {
DelayCrossCompartmentGrayMarking(src);
}
return false;
}
return dstZone->isGCMarkingBlackAndGray();
}
}
static bool ShouldTraceCrossCompartment(JSTracer* trc, JSObject* src,
Cell* dstCell) {
if (!trc->isMarkingTracer()) {
return true;
}
return ShouldMarkCrossCompartment(GCMarker::fromTracer(trc), src, dstCell);
}
static bool ShouldTraceCrossCompartment(JSTracer* trc, JSObject* src,
const Value& val) {
return val.isGCThing() &&
ShouldTraceCrossCompartment(trc, src, val.toGCThing());
}
static void AssertShouldMarkInZone(Cell* thing) {
MOZ_ASSERT(thing->asTenured().zone()->shouldMarkInZone());
}
static void AssertShouldMarkInZone(JSString* str) {
#ifdef DEBUG
Zone* zone = str->zone();
MOZ_ASSERT(zone->shouldMarkInZone() || zone->isAtomsZone());
#endif
}
static void AssertShouldMarkInZone(JS::Symbol* sym) {
#ifdef DEBUG
Zone* zone = sym->asTenured().zone();
MOZ_ASSERT(zone->shouldMarkInZone() || zone->isAtomsZone());
#endif
}
#ifdef DEBUG
void js::gc::AssertRootMarkingPhase(JSTracer* trc) {
MOZ_ASSERT_IF(trc->isMarkingTracer(),
trc->runtime()->gc.state() == State::NotActive ||
trc->runtime()->gc.state() == State::MarkRoots);
}
#endif
/*** Tracing Interface ******************************************************/
template <typename T>
bool DoCallback(JS::CallbackTracer* trc, T** thingp, const char* name);
template <typename T>
bool DoCallback(JS::CallbackTracer* trc, T* thingp, const char* name);
template <typename T>
void DoMarking(GCMarker* gcmarker, T* thing);
template <typename T>
void DoMarking(GCMarker* gcmarker, const T& thing);
template <typename T>
static void TraceExternalEdgeHelper(JSTracer* trc, T* thingp,
const char* name) {
MOZ_ASSERT(InternalBarrierMethods<T>::isMarkable(*thingp));
TraceEdgeInternal(trc, ConvertToBase(thingp), name);
}
JS_PUBLIC_API void js::UnsafeTraceManuallyBarrieredEdge(JSTracer* trc,
JSObject** thingp,
const char* name) {
TraceEdgeInternal(trc, ConvertToBase(thingp), name);
}
template <typename T>
static void UnsafeTraceRootHelper(JSTracer* trc, T* thingp, const char* name) {
MOZ_ASSERT(thingp);
js::TraceNullableRoot(trc, thingp, name);
}
namespace js {
class AbstractGeneratorObject;
class SavedFrame;
} // namespace js
#define DEFINE_TRACE_EXTERNAL_EDGE_FUNCTION(type) \
JS_PUBLIC_API void js::gc::TraceExternalEdge(JSTracer* trc, type* thingp, \
const char* name) { \
TraceExternalEdgeHelper(trc, thingp, name); \
}
// Define TraceExternalEdge for each public GC pointer type.
JS_FOR_EACH_PUBLIC_GC_POINTER_TYPE(DEFINE_TRACE_EXTERNAL_EDGE_FUNCTION)
JS_FOR_EACH_PUBLIC_TAGGED_GC_POINTER_TYPE(DEFINE_TRACE_EXTERNAL_EDGE_FUNCTION)
// Also, for the moment, define TraceExternalEdge for internal GC pointer types.
DEFINE_TRACE_EXTERNAL_EDGE_FUNCTION(AbstractGeneratorObject*)
DEFINE_TRACE_EXTERNAL_EDGE_FUNCTION(SavedFrame*)
#undef DEFINE_TRACE_EXTERNAL_EDGE_FUNCTION
#define DEFINE_UNSAFE_TRACE_ROOT_FUNCTION(type) \
JS_PUBLIC_API void JS::UnsafeTraceRoot(JSTracer* trc, type* thingp, \
const char* name) { \
UnsafeTraceRootHelper(trc, thingp, name); \
}
// Define UnsafeTraceRoot for each public GC pointer type.
JS_FOR_EACH_PUBLIC_GC_POINTER_TYPE(DEFINE_UNSAFE_TRACE_ROOT_FUNCTION)
JS_FOR_EACH_PUBLIC_TAGGED_GC_POINTER_TYPE(DEFINE_UNSAFE_TRACE_ROOT_FUNCTION)
// Also, for the moment, define UnsafeTraceRoot for internal GC pointer types.
DEFINE_UNSAFE_TRACE_ROOT_FUNCTION(AbstractGeneratorObject*)
DEFINE_UNSAFE_TRACE_ROOT_FUNCTION(SavedFrame*)
#undef DEFINE_UNSAFE_TRACE_ROOT_FUNCTION
namespace js {
namespace gc {
#define INSTANTIATE_INTERNAL_TRACE_FUNCTIONS(type) \
template bool TraceEdgeInternal<type>(JSTracer*, type*, const char*); \
template void TraceRangeInternal<type>(JSTracer*, size_t len, type*, \
const char*);
#define INSTANTIATE_INTERNAL_TRACE_FUNCTIONS_FROM_TRACEKIND(_1, type, _2, _3) \
INSTANTIATE_INTERNAL_TRACE_FUNCTIONS(type*)
JS_FOR_EACH_TRACEKIND(INSTANTIATE_INTERNAL_TRACE_FUNCTIONS_FROM_TRACEKIND)
JS_FOR_EACH_PUBLIC_TAGGED_GC_POINTER_TYPE(INSTANTIATE_INTERNAL_TRACE_FUNCTIONS)
#undef INSTANTIATE_INTERNAL_TRACE_FUNCTIONS_FROM_TRACEKIND
#undef INSTANTIATE_INTERNAL_TRACE_FUNCTIONS
} // namespace gc
} // namespace js
// In debug builds, makes a note of the current compartment before calling a
// trace hook or traceChildren() method on a GC thing.
class MOZ_RAII AutoSetTracingSource {
#ifdef DEBUG
GCMarker* marker = nullptr;
#endif
public:
template <typename T>
AutoSetTracingSource(JSTracer* trc, T* thing) {
#ifdef DEBUG
if (trc->isMarkingTracer() && thing) {
marker = GCMarker::fromTracer(trc);
MOZ_ASSERT(!marker->tracingZone);
marker->tracingZone = thing->asTenured().zone();
MOZ_ASSERT(!marker->tracingCompartment);
marker->tracingCompartment = thing->maybeCompartment();
}
#endif
}
~AutoSetTracingSource() {
#ifdef DEBUG
if (marker) {
marker->tracingZone = nullptr;
marker->tracingCompartment = nullptr;
}
#endif
}
};
// In debug builds, clear the trace hook compartment. This happens
// after the trace hook has called back into one of our trace APIs and we've
// checked the traced thing.
class MOZ_RAII AutoClearTracingSource {
#ifdef DEBUG
GCMarker* marker = nullptr;
JS::Zone* prevZone = nullptr;
Compartment* prevCompartment = nullptr;
#endif
public:
explicit AutoClearTracingSource(JSTracer* trc) {
#ifdef DEBUG
if (trc->isMarkingTracer()) {
marker = GCMarker::fromTracer(trc);
prevZone = marker->tracingZone;
marker->tracingZone = nullptr;
prevCompartment = marker->tracingCompartment;
marker->tracingCompartment = nullptr;
}
#endif
}
~AutoClearTracingSource() {
#ifdef DEBUG
if (marker) {
marker->tracingZone = prevZone;
marker->tracingCompartment = prevCompartment;
}
#endif
}
};
template <typename T>
void js::TraceManuallyBarrieredCrossCompartmentEdge(JSTracer* trc,
JSObject* src, T* dst,
const char* name) {
// Clear expected compartment for cross-compartment edge.
AutoClearTracingSource acts(trc);
if (ShouldTraceCrossCompartment(trc, src, *dst)) {
TraceEdgeInternal(trc, dst, name);
}
}
template void js::TraceManuallyBarrieredCrossCompartmentEdge<Value>(
JSTracer*, JSObject*, Value*, const char*);
template void js::TraceManuallyBarrieredCrossCompartmentEdge<JSObject*>(
JSTracer*, JSObject*, JSObject**, const char*);
template void js::TraceManuallyBarrieredCrossCompartmentEdge<BaseScript*>(
JSTracer*, JSObject*, BaseScript**, const char*);
template <typename T>
void js::TraceWeakMapKeyEdgeInternal(JSTracer* trc, Zone* weakMapZone,
T** thingp, const char* name) {
// We can't use ShouldTraceCrossCompartment here because that assumes the
// source of the edge is a CCW object which could be used to delay gray
// marking. Instead, assert that the weak map zone is in the same marking
// state as the target thing's zone and therefore we can go ahead and mark it.
#ifdef DEBUG
auto thing = *thingp;
if (trc->isMarkingTracer()) {
MOZ_ASSERT(weakMapZone->isGCMarking());
MOZ_ASSERT(weakMapZone->gcState() == thing->zone()->gcState());
}
#endif
// Clear expected compartment for cross-compartment edge.
AutoClearTracingSource acts(trc);
TraceEdgeInternal(trc, thingp, name);
}
template void js::TraceWeakMapKeyEdgeInternal<JSObject>(JSTracer*, Zone*,
JSObject**,
const char*);
template void js::TraceWeakMapKeyEdgeInternal<BaseScript>(JSTracer*, Zone*,
BaseScript**,
const char*);
template <typename T>
void js::TraceProcessGlobalRoot(JSTracer* trc, T* thing, const char* name) {
AssertRootMarkingPhase(trc);
MOZ_ASSERT(ThingIsPermanentAtomOrWellKnownSymbol(thing));
// We have to mark permanent atoms and well-known symbols through a special
// method because the default DoMarking implementation automatically skips
// them. Fortunately, atoms (permanent and non) cannot refer to other GC
// things so they do not need to go through the mark stack and may simply
// be marked directly. Moreover, well-known symbols can refer only to
// permanent atoms, so likewise require no subsquent marking.
CheckTracedThing(trc, *ConvertToBase(&thing));
AutoClearTracingSource acts(trc);
if (trc->isMarkingTracer()) {
thing->asTenured().markIfUnmarked(gc::MarkColor::Black);
} else {
DoCallback(trc->asCallbackTracer(), ConvertToBase(&thing), name);
}
}
template void js::TraceProcessGlobalRoot<JSAtom>(JSTracer*, JSAtom*,
const char*);
template void js::TraceProcessGlobalRoot<JS::Symbol>(JSTracer*, JS::Symbol*,
const char*);
static Cell* TraceGenericPointerRootAndType(JSTracer* trc, Cell* thing,
JS::TraceKind kind,
const char* name) {
return MapGCThingTyped(thing, kind, [trc, name](auto t) -> Cell* {
TraceRoot(trc, &t, name);
return t;
});
}
void js::TraceGenericPointerRoot(JSTracer* trc, Cell** thingp,
const char* name) {
MOZ_ASSERT(thingp);
Cell* thing = *thingp;
if (!thing) {
return;
}
Cell* traced =
TraceGenericPointerRootAndType(trc, thing, thing->getTraceKind(), name);
if (traced != thing) {
*thingp = traced;
}
}
void js::TraceManuallyBarrieredGenericPointerEdge(JSTracer* trc, Cell** thingp,
const char* name) {
MOZ_ASSERT(thingp);
Cell* thing = *thingp;
if (!*thingp) {
return;
}
auto traced = MapGCThingTyped(thing, thing->getTraceKind(),
[trc, name](auto t) -> Cell* {
TraceManuallyBarrieredEdge(trc, &t, name);
return t;
});
if (traced != thing) {
*thingp = traced;
}
}
void js::TraceGCCellPtrRoot(JSTracer* trc, JS::GCCellPtr* thingp,
const char* name) {
Cell* thing = thingp->asCell();
if (!thing) {
return;
}
Cell* traced =
TraceGenericPointerRootAndType(trc, thing, thingp->kind(), name);
if (!traced) {
*thingp = JS::GCCellPtr();
} else if (traced != thingp->asCell()) {
*thingp = JS::GCCellPtr(traced, thingp->kind());
}
}
// This method is responsible for dynamic dispatch to the real tracer
// implementation. Consider replacing this choke point with virtual dispatch:
// a sufficiently smart C++ compiler may be able to devirtualize some paths.
template <typename T>
bool js::gc::TraceEdgeInternal(JSTracer* trc, T* thingp, const char* name) {
#define IS_SAME_TYPE_OR(name, type, _, _1) std::is_same_v<type*, T> ||
static_assert(JS_FOR_EACH_TRACEKIND(IS_SAME_TYPE_OR)
std::is_same_v<T, JS::Value> ||
std::is_same_v<T, jsid> || std::is_same_v<T, TaggedProto>,
"Only the base cell layout types are allowed into "
"marking/tracing internals");
#undef IS_SAME_TYPE_OR
if (trc->isMarkingTracer()) {
DoMarking(GCMarker::fromTracer(trc), *thingp);
return true;
}
if (trc->isTenuringTracer()) {
static_cast<TenuringTracer*>(trc)->traverse(thingp);
return true;
}
MOZ_ASSERT(trc->isCallbackTracer());
return DoCallback(trc->asCallbackTracer(), thingp, name);
}
template <typename T>
void js::gc::TraceRangeInternal(JSTracer* trc, size_t len, T* vec,
const char* name) {
JS::AutoTracingIndex index(trc);
for (auto i : IntegerRange(len)) {
if (InternalBarrierMethods<T>::isMarkable(vec[i])) {
TraceEdgeInternal(trc, &vec[i], name);
}
++index;
}
}
/*** GC Marking Interface ***************************************************/
namespace js {
using HasNoImplicitEdgesType = bool;
template <typename T>
struct ImplicitEdgeHolderType {
using Type = HasNoImplicitEdgesType;
};
// For now, we only handle JSObject* and BaseScript* keys, but the linear time
// algorithm can be easily extended by adding in more types here, then making
// GCMarker::traverse<T> call markImplicitEdges.
template <>
struct ImplicitEdgeHolderType<JSObject*> {
using Type = JSObject*;
};
template <>
struct ImplicitEdgeHolderType<BaseScript*> {
using Type = BaseScript*;
};
void GCMarker::markEphemeronValues(gc::Cell* markedCell,
WeakEntryVector& values) {
DebugOnly<size_t> initialLen = values.length();
for (const auto& markable : values) {
markable.weakmap->markKey(this, markedCell, markable.key);
}
// The vector should not be appended to during iteration because the key is
// already marked, and even in cases where we have a multipart key, we
// should only be inserting entries for the unmarked portions.
MOZ_ASSERT(values.length() == initialLen);
}
template <typename T>
void GCMarker::markImplicitEdgesHelper(T markedThing) {
if (!isWeakMarking()) {
return;
}
Zone* zone = markedThing->asTenured().zone();
MOZ_ASSERT(zone->isGCMarking());
MOZ_ASSERT(!zone->isGCSweeping());
auto p = zone->gcWeakKeys().get(markedThing);
if (!p) {
return;
}
WeakEntryVector& markables = p->value;
// markedThing might be a key in a debugger weakmap, which can end up marking
// values that are in a different compartment.
AutoClearTracingSource acts(this);
markEphemeronValues(markedThing, markables);
markables.clear(); // If key address is reused, it should do nothing
}
template <>
void GCMarker::markImplicitEdgesHelper(HasNoImplicitEdgesType) {}
template <typename T>
void GCMarker::markImplicitEdges(T* thing) {
markImplicitEdgesHelper<typename ImplicitEdgeHolderType<T*>::Type>(thing);
}
template void GCMarker::markImplicitEdges(JSObject*);
template void GCMarker::markImplicitEdges(BaseScript*);
} // namespace js
template <typename T>
static inline bool ShouldMark(GCMarker* gcmarker, T thing) {
// Don't trace things that are owned by another runtime.
if (IsOwnedByOtherRuntime(gcmarker->runtime(), thing)) {
return false;
}
// Don't mark things outside a zone if we are in a per-zone GC.
return thing->zone()->shouldMarkInZone();
}
template <>
bool ShouldMark<JSObject*>(GCMarker* gcmarker, JSObject* obj) {
// Don't trace things that are owned by another runtime.
if (IsOwnedByOtherRuntime(gcmarker->runtime(), obj)) {
return false;
}
// We may mark a Nursery thing outside the context of the
// MinorCollectionTracer because of a pre-barrier. The pre-barrier is not
// needed in this case because we perform a minor collection before each
// incremental slice.
if (IsInsideNursery(obj)) {
return false;
}
// Don't mark things outside a zone if we are in a per-zone GC. It is
// faster to check our own arena, which we can do since we know that
// the object is tenured.
return obj->asTenured().zone()->shouldMarkInZone();
}
// JSStrings can also be in the nursery. See ShouldMark<JSObject*> for comments.
template <>
bool ShouldMark<JSString*>(GCMarker* gcmarker, JSString* str) {
if (IsOwnedByOtherRuntime(gcmarker->runtime(), str)) {
return false;
}
if (IsInsideNursery(str)) {
return false;
}
return str->asTenured().zone()->shouldMarkInZone();
}
// BigInts can also be in the nursery. See ShouldMark<JSObject*> for comments.
template <>
bool ShouldMark<JS::BigInt*>(GCMarker* gcmarker, JS::BigInt* bi) {
if (IsOwnedByOtherRuntime(gcmarker->runtime(), bi)) {
return false;
}
if (IsInsideNursery(bi)) {
return false;
}
return bi->asTenured().zone()->shouldMarkInZone();
}
template <typename T>
void DoMarking(GCMarker* gcmarker, T* thing) {
// Do per-type marking precondition checks.
if (!ShouldMark(gcmarker, thing)) {
return;
}
CheckTracedThing(gcmarker, thing);
AutoClearTracingSource acts(gcmarker);
gcmarker->traverse(thing);
// Mark the compartment as live.
SetMaybeAliveFlag(thing);
}
template <typename T>
void DoMarking(GCMarker* gcmarker, const T& thing) {
ApplyGCThingTyped(thing, [gcmarker](auto t) { DoMarking(gcmarker, t); });
}
JS_PUBLIC_API void js::gc::PerformIncrementalReadBarrier(JS::GCCellPtr thing) {
// Optimized marking for read barriers. This is called from
// ExposeGCThingToActiveJS which has already checked the prerequisites for
// performing a read barrier. This means we can skip a bunch of checks and
// call info the tracer directly.
MOZ_ASSERT(thing);
MOZ_ASSERT(!JS::RuntimeHeapIsMajorCollecting());
TenuredCell* cell = &thing.asCell()->asTenured();
Zone* zone = cell->zone();
MOZ_ASSERT(zone->needsIncrementalBarrier());
// Skip disptaching on known tracer type.
GCMarker* gcmarker = GCMarker::fromTracer(zone->barrierTracer());
// Mark the argument, as DoMarking above.
ApplyGCThingTyped(thing, [gcmarker](auto thing) {
MOZ_ASSERT(ShouldMark(gcmarker, thing));
CheckTracedThing(gcmarker, thing);
AutoClearTracingSource acts(gcmarker);
gcmarker->traverse(thing);
});
}
// The simplest traversal calls out to the fully generic traceChildren function
// to visit the child edges. In the absence of other traversal mechanisms, this
// function will rapidly grow the stack past its bounds and crash the process.
// Thus, this generic tracing should only be used in cases where subsequent
// tracing will not recurse.
template <typename T>
void js::GCMarker::markAndTraceChildren(T* thing) {
if (ThingIsPermanentAtomOrWellKnownSymbol(thing)) {
return;
}
if (mark(thing)) {
AutoSetTracingSource asts(this, thing);
thing->traceChildren(this);
}
}
namespace js {
template <>
void GCMarker::traverse(BaseShape* thing) {
markAndTraceChildren(thing);
}
template <>
void GCMarker::traverse(JS::Symbol* thing) {
markAndTraceChildren(thing);
}
template <>
void GCMarker::traverse(JS::BigInt* thing) {
markAndTraceChildren(thing);
}
template <>
void GCMarker::traverse(RegExpShared* thing) {
markAndTraceChildren(thing);
}
} // namespace js
// Strings, Shapes, and Scopes are extremely common, but have simple patterns of
// recursion. We traverse trees of these edges immediately, with aggressive,
// manual inlining, implemented by eagerlyTraceChildren.
template <typename T>
void js::GCMarker::markAndScan(T* thing) {
if (ThingIsPermanentAtomOrWellKnownSymbol(thing)) {
return;
}
if (mark(thing)) {
eagerlyMarkChildren(thing);
}
}
namespace js {
template <>
void GCMarker::traverse(JSString* thing) {
markAndScan(thing);
}
template <>
void GCMarker::traverse(Shape* thing) {
markAndScan(thing);
}
template <>
void GCMarker::traverse(js::Scope* thing) {
markAndScan(thing);
}
} // namespace js
// Object and ObjectGroup are extremely common and can contain arbitrarily
// nested graphs, so are not trivially inlined. In this case we use a mark
// stack to control recursion. JitCode shares none of these properties, but is
// included for historical reasons. JSScript normally cannot recurse, but may
// be used as a weakmap key and thereby recurse into weakmapped values.
template <typename T>
void js::GCMarker::markAndPush(T* thing) {
if (!mark(thing)) {
return;
}
pushTaggedPtr(thing);
}
namespace js {
template <>
void GCMarker::traverse(JSObject* thing) {
markAndPush(thing);
}
template <>
void GCMarker::traverse(ObjectGroup* thing) {
markAndPush(thing);
}
template <>
void GCMarker::traverse(jit::JitCode* thing) {
markAndPush(thing);
}
template <>
void GCMarker::traverse(BaseScript* thing) {
markAndPush(thing);
}
} // namespace js
namespace js {
template <>
void GCMarker::traverse(AccessorShape* thing) {