author Jon Coppeard <jcoppeard@mozilla.com>
Wed, 06 Mar 2019 16:38:25 +0000
changeset 520784 1b4fd78107e2bcf7fe0f44038176ca745b07cd88
parent 519776 f99b937e9e7ce91e7d648a37251d4af8d1d6da68
child 520786 b8137cbaf9cfa4f4c45cb9bd82584b4375ba2662
permissions -rw-r--r--
Bug 1532376 - Fix places where we don't respect the shouldPretenure flag when creating an object r=jandem This adds an overload of GetInitialHeap that takes an ObjectGroup* instead of a Class* and also takes into account whether the group's shouldPreTenure flag is set. I moved this to JSObject-inl.h too. I removed the heap parameter in a few places, in particular in NewDenseCopyOnWriteArray which required a bunch of changes elsewhere including the JITs. I left the heap parameter intact for environment objects where we may have reason prefer these objects to be allocated in the tenure heap. It's possible we should just remove all these parameters too and make allocation more uniform. Differential Revision: https://phabricator.services.mozilla.com/D22324

/* -*- 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/Allocator.h"
#include "gc/GCTrace.h"
#include "proxy/DeadObjectProxy.h"
#include "vm/Realm.h"

#include "gc/ObjectKind-inl.h"
#include "vm/JSObject-inl.h"
#include "vm/TypeInference-inl.h"

using namespace js;

static gc::AllocKind GetProxyGCObjectKind(const Class* clasp,
                                          const BaseProxyHandler* handler,
                                          const Value& priv) {

  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);

      js::detail::ProxyValueArray::sizeOf(nreserved) % sizeof(Value) == 0,
      "ProxyValueArray must be a multiple of Value");

  uint32_t nslots =
      js::detail::ProxyValueArray::sizeOf(nreserved) / sizeof(Value);
  MOZ_ASSERT(nslots <= NativeObject::MAX_FIXED_SLOTS);

  gc::AllocKind kind = gc::GetGCObjectKind(nslots);
  if (handler->finalizeInBackground(priv)) {
    kind = GetBackgroundAllocKind(kind);

  return kind;

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

  const Class* clasp = options.clasp();

#ifdef DEBUG
                cx->compartment() == proto.toObject()->compartment());
  if (priv.isGCThing()) {

   * Eagerly mark properties unknown for proxies, so we don't try to track
   * their properties and so that we don't need to walk the compartment if
   * their prototype changes later.  But don't do this for DOM proxies,
   * because we want to be able to keep track of them in typesets in useful
   * ways.
  if (proto.isObject() && !options.singleton() && !clasp->isDOMClass()) {
    ObjectGroupRealm& realm = ObjectGroupRealm::getForNewObject(cx);
    RootedObject protoObj(cx, proto.toObject());
    if (!JSObject::setNewGroupUnknown(cx, realm, clasp, protoObj)) {
      return nullptr;

  // Ensure that the wrapper has the same lifetime assumptions as the
  // wrappee. Prefer to allocate in the nursery, when possible.
  NewObjectKind newKind = NurseryAllocatedProxy;
  if (options.singleton()) {
    MOZ_ASSERT(priv.isNull() ||
               (priv.isGCThing() && priv.toGCThing()->isTenured()));
    newKind = SingletonObject;
  } else if ((priv.isGCThing() && priv.toGCThing()->isTenured()) ||
             !handler->canNurseryAllocate()) {
    newKind = TenuredObject;

  gc::AllocKind allocKind = GetProxyGCObjectKind(clasp, handler, priv);

  AutoSetNewObjectMetadata metadata(cx);
  // Note: this will initialize the object's |data| to strange values, but we
  // will immediately overwrite those below.
  ProxyObject* proxy;
                            create(cx, clasp, proto, allocKind, newKind));


  detail::ProxyValueArray* values = detail::GetProxyDataLayout(proxy)->values();

  proxy->data.handler = handler;
  if (IsCrossCompartmentWrapper(proxy)) {
    MOZ_ASSERT(cx->global() == &cx->compartment()->globalForNewCCW());
  } else {

  /* Don't track types of properties of non-DOM and non-singleton proxies. */
  if (newKind != SingletonObject && !clasp->isDOMClass()) {
    MarkObjectGroupUnknownProperties(cx, proxy->group());

  return proxy;

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

void ProxyObject::setCrossCompartmentPrivate(const Value& priv) {

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

inline void ProxyObject::setPrivate(const Value& priv) {
  MOZ_ASSERT_IF(IsMarkedBlack(this) && priv.isGCThing(),
  *slotOfPrivate() = priv;

void ProxyObject::nuke() {
  // Clear the target reference and replaced it with a value that encodes
  // various information about the original target.

  // Update the handler to make this a DeadObjectProxy.

  // 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.

/* static */ JS::Result<ProxyObject*, JS::OOM&> ProxyObject::create(
    JSContext* cx, const Class* clasp, Handle<TaggedProto> proto,
    gc::AllocKind allocKind, NewObjectKind newKind) {

  Realm* realm = cx->realm();
  RootedObjectGroup group(cx);
  RootedShape shape(cx);

  // Try to look up the group and shape in the NewProxyCache.
  if (!realm->newProxyCache.lookup(clasp, proto, group.address(),
                                   shape.address())) {
    group = ObjectGroup::defaultNewGroup(cx, clasp, proto, nullptr);
    if (!group) {
      return cx->alreadyReportedOOM();

    shape = EmptyShape::getInitialShape(cx, clasp, proto, /* nfixed = */ 0);
    if (!shape) {
      return cx->alreadyReportedOOM();

    MOZ_ASSERT(group->realm() == realm);
    realm->newProxyCache.add(group, shape);

  gc::InitialHeap heap = GetInitialHeap(newKind, group);
  debugCheckNewObject(group, shape, allocKind, heap);

  JSObject* obj = js::Allocate<JSObject>(cx, allocKind, /* nDynamicSlots = */ 0,
                                         heap, clasp);
  if (!obj) {
    return cx->alreadyReportedOOM();

  ProxyObject* pobj = static_cast<ProxyObject*>(obj);

  cx->realm()->setObjectPendingMetadata(cx, pobj);


  if (newKind == SingletonObject) {
    Rooted<ProxyObject*> pobjRoot(cx, pobj);
    if (!JSObject::setSingleton(cx, pobjRoot)) {
      return cx->alreadyReportedOOM();
    pobj = pobjRoot;

  return pobj;

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