tor-browser

ProxyObject.cpp (6908B)

---

/* -*- 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 "vm/ProxyObject.h"

#include "gc/GCProbes.h"
#include "gc/Marking.h"
#include "gc/Zone.h"
#include "proxy/DeadObjectProxy.h"
#include "vm/Compartment.h"
#include "vm/Realm.h"

#include "gc/ObjectKind-inl.h"
#include "vm/JSContext-inl.h"

using namespace js;

static gc::AllocKind GetProxyGCObjectKind(const JSClass* clasp,
                                         const BaseProxyHandler* handler,
                                         const Value& priv,
                                         bool withInlineValues) {
 MOZ_ASSERT(clasp->isProxyObject());

 uint32_t nreserved = JSCLASS_RESERVED_SLOTS(clasp);

 // For now assert each Proxy Class has at least 1 reserved slot. This is
 // not a hard requirement, but helps catch Classes that need an explicit
 // JSCLASS_HAS_RESERVED_SLOTS since bug 1360523.
 MOZ_ASSERT(nreserved > 0);

 uint32_t nslots = 0;
 if (withInlineValues) {
   nslots = detail::ProxyValueArray::allocCount(nreserved);
 }

 MOZ_ASSERT(nslots <= NativeObject::MAX_FIXED_SLOTS);
 gc::AllocKind kind = gc::GetGCObjectKind(nslots);
 gc::FinalizeKind finalizeKind;

 // Bug 1957589: Support non-finalized proxies as well.
 if (handler->finalizeInBackground(priv)) {
   finalizeKind = gc::FinalizeKind::Background;
 } else {
   finalizeKind = gc::FinalizeKind::Foreground;
 }

 return gc::GetFinalizedAllocKind(kind, finalizeKind);
}

void ProxyObject::init(const BaseProxyHandler* handler, HandleValue priv,
                      JSContext* cx) {
 setInlineValueArray();

 detail::ProxyValueArray* values = detail::GetProxyDataLayout(this)->values();
 values->init(numReservedSlots());

 data.handler = handler;

 if (IsCrossCompartmentWrapper(this)) {
   MOZ_ASSERT(cx->global() == &cx->compartment()->globalForNewCCW());
   setCrossCompartmentPrivate(priv);
 } else {
   setSameCompartmentPrivate(priv);
 }

 // The expando slot is nullptr until required by the installation of
 // a private field.
 setExpando(nullptr);
}

/* static */
ProxyObject* ProxyObject::New(JSContext* cx, const BaseProxyHandler* handler,
                             HandleValue priv, TaggedProto proto_,
                             const JSClass* clasp) {
 Rooted<TaggedProto> proto(cx, proto_);

 MOZ_ASSERT(!clasp->isNativeObject());
 MOZ_ASSERT(clasp->isProxyObject());
 MOZ_ASSERT(isValidProxyClass(clasp));
 MOZ_ASSERT(clasp->shouldDelayMetadataBuilder());
 MOZ_ASSERT_IF(proto.isObject(),
               cx->compartment() == proto.toObject()->compartment());
 MOZ_ASSERT(clasp->hasFinalize());

#ifdef DEBUG
 if (priv.isGCThing()) {
   JS::AssertCellIsNotGray(priv.toGCThing());
 }
#endif

 gc::AllocKind allocKind = GetProxyGCObjectKind(clasp, handler, priv,
                                                /* withInlineValues = */ true);

 Realm* realm = cx->realm();

 AutoSetNewObjectMetadata metadata(cx);
 // Try to look up the shape in the NewProxyCache.
 Rooted<Shape*> shape(cx);
 if (!realm->newProxyCache.lookup(clasp, proto, shape.address())) {
   shape = ProxyShape::getShape(cx, clasp, realm, proto, ObjectFlags());
   if (!shape) {
     return nullptr;
   }

   realm->newProxyCache.add(shape);
 }

 MOZ_ASSERT(shape->realm() == realm);
 MOZ_ASSERT(!IsAboutToBeFinalizedUnbarriered(shape.get()));

 // Ensure that the wrapper has the same lifetime assumptions as the
 // wrappee. Prefer to allocate in the nursery, when possible.
 gc::Heap heap;
 if ((priv.isGCThing() && priv.toGCThing()->isTenured()) ||
     !handler->canNurseryAllocate()) {
   heap = gc::Heap::Tenured;
 } else {
   heap = gc::Heap::Default;
 }

 debugCheckNewObject(shape, allocKind, heap);

 ProxyObject* proxy = cx->newCell<ProxyObject>(allocKind, heap, clasp);
 if (!proxy) {
   return nullptr;
 }

 proxy->initShape(shape);

 MOZ_ASSERT(clasp->shouldDelayMetadataBuilder());
 realm->setObjectPendingMetadata(proxy);

 gc::gcprobes::CreateObject(proxy);

 proxy->init(handler, priv, cx);

 return proxy;
}

gc::AllocKind ProxyObject::allocKindForTenure() const {
 Value priv = private_();
 return GetProxyGCObjectKind(getClass(), data.handler, priv,
                             usingInlineValueArray());
}

void ProxyObject::setCrossCompartmentPrivate(const Value& priv) {
 setPrivate(priv);
}

void ProxyObject::setSameCompartmentPrivate(const Value& priv) {
 MOZ_ASSERT(IsObjectValueInCompartment(priv, compartment()));
 setPrivate(priv);
}

inline void ProxyObject::setPrivate(const Value& priv) {
#ifdef DEBUG
 JS::AssertValueIsNotGray(priv);
#endif
 *slotOfPrivate() = priv;
}

void ProxyObject::setExpando(JSObject* expando) {
 // Ensure we're in the same compartment as the proxy object: Don't want the
 // expando to end up as a CCW.
 MOZ_ASSERT_IF(expando, expando->compartment() == compartment());

 // Ensure that we don't accidentally end up pointing to a
 // grey object, which would violate GC invariants.
 MOZ_ASSERT_IF(!zone()->isGCPreparing() && isMarkedBlack() && expando,
               !JS::GCThingIsMarkedGray(JS::GCCellPtr(expando)));

 *slotOfExpando() = ObjectOrNullValue(expando);
}

void ProxyObject::nuke() {
 // Notify the zone that a delegate is no longer a delegate. Be careful not to
 // expose this pointer, because it has already been removed from the wrapper
 // map yet we have assertions during tracing that will verify that it is
 // still present.
 JSObject* delegate = UncheckedUnwrapWithoutExpose(this);
 if (delegate != this) {
   delegate->zone()->beforeClearDelegate(this, delegate);
 }

 // Clear the target reference and replaced it with a value that encodes
 // various information about the original target.
 setSameCompartmentPrivate(DeadProxyTargetValue(this));

 // Clear out the expando
 setExpando(nullptr);

 // Update the handler to make this a DeadObjectProxy.
 setHandler(&DeadObjectProxy::singleton);

 // The proxy's reserved slots are not cleared and will continue to be
 // traced. This avoids the possibility of triggering write barriers while
 // nuking proxies in dead compartments which could otherwise cause those
 // compartments to be kept alive. Note that these are slots cannot hold
 // cross compartment pointers, so this cannot cause the target compartment
 // to leak.
}

JS_PUBLIC_API void js::detail::SetValueInProxy(Value* slot,
                                              const Value& value) {
 // Slots in proxies are not GCPtr<Value>s, so do a cast whenever assigning
 // values to them which might trigger a barrier.
 *reinterpret_cast<GCPtr<Value>*>(slot) = value;
}