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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 "vm/Watchtower.h"
#include "js/CallAndConstruct.h"
#include "vm/Compartment.h"
#include "vm/JSContext.h"
#include "vm/JSObject.h"
#include "vm/NativeObject.h"
#include "vm/PlainObject.h"
#include "vm/Realm.h"
#include "vm/Compartment-inl.h"
#include "vm/JSObject-inl.h"
#include "vm/NativeObject-inl.h"
#include "vm/Realm-inl.h"
#include "vm/Shape-inl.h"
using namespace js;
static bool AddToWatchtowerLog(JSContext* cx, const char* kind,
HandleObject obj, HandleValue extra) {
// Add an object storing {kind, object, extra} to the log for testing
// purposes.
MOZ_ASSERT(obj->useWatchtowerTestingLog());
RootedString kindString(cx, NewStringCopyZ<CanGC>(cx, kind));
if (!kindString) {
return false;
}
Rooted<PlainObject*> logObj(cx, NewPlainObjectWithProto(cx, nullptr));
if (!logObj) {
return false;
}
if (!JS_DefineProperty(cx, logObj, "kind", kindString, JSPROP_ENUMERATE)) {
return false;
}
if (!JS_DefineProperty(cx, logObj, "object", obj, JSPROP_ENUMERATE)) {
return false;
}
if (!JS_DefineProperty(cx, logObj, "extra", extra, JSPROP_ENUMERATE)) {
return false;
}
if (!cx->runtime()->watchtowerTestingLog->append(logObj)) {
ReportOutOfMemory(cx);
return false;
}
return true;
}
static bool ReshapeForShadowedProp(JSContext* cx, Handle<NativeObject*> obj,
HandleId id) {
// |obj| has been used as the prototype of another object. Check if we're
// shadowing a property on its proto chain. In this case we need to reshape
// that object for shape teleporting to work correctly.
//
// See also the 'Shape Teleporting Optimization' comment in jit/CacheIR.cpp.
MOZ_ASSERT(obj->isUsedAsPrototype());
// Lookups on integer ids cannot be cached through prototypes.
if (id.isInt()) {
return true;
}
RootedObject proto(cx, obj->staticPrototype());
while (proto) {
// Lookups will not be cached through non-native protos.
if (!proto->is<NativeObject>()) {
break;
}
if (proto->as<NativeObject>().contains(cx, id)) {
return JSObject::setInvalidatedTeleporting(cx, proto);
}
proto = proto->staticPrototype();
}
return true;
}
static void InvalidateMegamorphicCache(JSContext* cx,
Handle<NativeObject*> obj) {
// The megamorphic cache only checks the receiver object's shape. We need to
// invalidate the cache when a prototype object changes its set of properties,
// to account for cached properties that are deleted, turned into an accessor
// property, or shadowed by another object on the proto chain.
MOZ_ASSERT(obj->isUsedAsPrototype());
cx->caches().megamorphicCache.bumpGeneration();
cx->caches().megamorphicSetPropCache->bumpGeneration();
}
void MaybePopReturnFuses(JSContext* cx, Handle<NativeObject*> nobj) {
JSObject* objectProto = &cx->global()->getObjectPrototype();
if (nobj == objectProto) {
nobj->realm()->realmFuses.objectPrototypeHasNoReturnProperty.popFuse(
cx, nobj->realm()->realmFuses);
return;
}
JSObject* iteratorProto = cx->global()->maybeGetIteratorPrototype();
if (nobj == iteratorProto) {
nobj->realm()->realmFuses.iteratorPrototypeHasNoReturnProperty.popFuse(
cx, nobj->realm()->realmFuses);
return;
}
JSObject* arrayIterProto = cx->global()->maybeGetArrayIteratorPrototype();
if (nobj == arrayIterProto) {
cx->realm()->realmFuses.arrayIteratorPrototypeHasNoReturnProperty.popFuse(
cx, nobj->realm()->realmFuses);
return;
}
}
// static
bool Watchtower::watchPropertyAddSlow(JSContext* cx, Handle<NativeObject*> obj,
HandleId id) {
MOZ_ASSERT(watchesPropertyAdd(obj));
if (obj->isUsedAsPrototype()) {
if (!ReshapeForShadowedProp(cx, obj, id)) {
return false;
}
if (!id.isInt()) {
InvalidateMegamorphicCache(cx, obj);
}
if (id == NameToId(cx->names().return_)) {
MaybePopReturnFuses(cx, obj);
}
}
if (MOZ_UNLIKELY(obj->useWatchtowerTestingLog())) {
RootedValue val(cx, IdToValue(id));
if (!AddToWatchtowerLog(cx, "add-prop", obj, val)) {
return false;
}
}
return true;
}
static bool ReshapeForProtoMutation(JSContext* cx, HandleObject obj) {
// To avoid the JIT guarding on each prototype in the proto chain to detect
// prototype mutation, we can instead reshape the rest of the proto chain such
// that a guard on any of them is sufficient. To avoid excessive reshaping and
// invalidation, we apply heuristics to decide when to apply this and when
// to require a guard.
//
// There are two cases:
//
// (1) The object is not marked IsUsedAsPrototype. This is the common case.
// Because shape implies proto, we rely on the caller changing the
// object's shape. The JIT guards on this object's shape or prototype so
// there's nothing we have to do here for objects on the proto chain.
//
// (2) The object is marked IsUsedAsPrototype. This implies the object may be
// participating in shape teleporting. To invalidate JIT ICs depending on
// the proto chain being unchanged, set the InvalidatedTeleporting shape
// flag for this object and objects on its proto chain.
//
// This flag disables future shape teleporting attempts, so next time this
// happens the loop below will be a no-op.
//
// NOTE: We only handle NativeObjects and don't propagate reshapes through
// any non-native objects on the chain.
//
// See Also:
// - GeneratePrototypeGuards
// - GeneratePrototypeHoleGuards
MOZ_ASSERT(obj->isUsedAsPrototype());
RootedObject pobj(cx, obj);
while (pobj && pobj->is<NativeObject>()) {
if (!pobj->hasInvalidatedTeleporting()) {
if (!JSObject::setInvalidatedTeleporting(cx, pobj)) {
return false;
}
}
pobj = pobj->staticPrototype();
}
return true;
}
static bool WatchProtoChangeImpl(JSContext* cx, HandleObject obj) {
if (!obj->isUsedAsPrototype()) {
return true;
}
if (!ReshapeForProtoMutation(cx, obj)) {
return false;
}
if (obj->is<NativeObject>()) {
InvalidateMegamorphicCache(cx, obj.as<NativeObject>());
NativeObject* nobj = &obj->as<NativeObject>();
if (nobj == cx->global()->maybeGetArrayIteratorPrototype()) {
nobj->realm()->realmFuses.arrayIteratorPrototypeHasIteratorProto.popFuse(
cx, nobj->realm()->realmFuses);
}
if (nobj == cx->global()->maybeGetIteratorPrototype()) {
nobj->realm()->realmFuses.iteratorPrototypeHasObjectProto.popFuse(
cx, nobj->realm()->realmFuses);
}
}
return true;
}
// static
bool Watchtower::watchProtoChangeSlow(JSContext* cx, HandleObject obj) {
MOZ_ASSERT(watchesProtoChange(obj));
if (!WatchProtoChangeImpl(cx, obj)) {
return false;
}
if (MOZ_UNLIKELY(obj->useWatchtowerTestingLog())) {
if (!AddToWatchtowerLog(cx, "proto-change", obj,
JS::UndefinedHandleValue)) {
return false;
}
}
return true;
}
static void MaybePopArrayIteratorFuse(JSContext* cx, NativeObject* obj,
jsid id) {
if (!id.isWellKnownSymbol(JS::SymbolCode::iterator)) {
return;
}
JSObject* originalArrayPrototype = obj->global().maybeGetArrayPrototype();
if (!originalArrayPrototype) {
return;
}
if (obj != originalArrayPrototype) {
return;
}
obj->realm()->realmFuses.arrayPrototypeIteratorFuse.popFuse(
cx, obj->realm()->realmFuses);
}
static void MaybePopArrayIteratorPrototypeNextFuse(JSContext* cx,
NativeObject* obj, jsid id) {
JSObject* originalArrayIteratorPrototoype =
obj->global().maybeGetArrayIteratorPrototype();
if (!originalArrayIteratorPrototoype) {
return;
}
if (obj != originalArrayIteratorPrototoype) {
return;
}
PropertyKey nextId = NameToId(cx->names().next);
if (id != nextId) {
return;
}
obj->realm()->realmFuses.arrayPrototypeIteratorNextFuse.popFuse(
cx, obj->realm()->realmFuses);
}
static void MaybePopFuses(JSContext* cx, NativeObject* obj, jsid id) {
// Handle a write to Array.prototype[@@iterator]
MaybePopArrayIteratorFuse(cx, obj, id);
// Handle a write to Array.prototype[@@iterator].next
MaybePopArrayIteratorPrototypeNextFuse(cx, obj, id);
}
// static
bool Watchtower::watchPropertyRemoveSlow(JSContext* cx,
Handle<NativeObject*> obj,
HandleId id) {
MOZ_ASSERT(watchesPropertyRemove(obj));
if (obj->isUsedAsPrototype() && !id.isInt()) {
InvalidateMegamorphicCache(cx, obj);
}
if (obj->isGenerationCountedGlobal()) {
obj->as<GlobalObject>().bumpGenerationCount();
}
if (MOZ_UNLIKELY(obj->hasFuseProperty())) {
MaybePopFuses(cx, obj, id);
}
if (MOZ_UNLIKELY(obj->useWatchtowerTestingLog())) {
RootedValue val(cx, IdToValue(id));
if (!AddToWatchtowerLog(cx, "remove-prop", obj, val)) {
return false;
}
}
return true;
}
// static
bool Watchtower::watchPropertyChangeSlow(JSContext* cx,
Handle<NativeObject*> obj, HandleId id,
PropertyFlags flags) {
MOZ_ASSERT(watchesPropertyChange(obj));
if (obj->isUsedAsPrototype() && !id.isInt()) {
InvalidateMegamorphicCache(cx, obj);
}
if (obj->isGenerationCountedGlobal()) {
// The global generation counter only cares whether a property
// changes from data property to accessor or vice-versa. Changing
// the flags on a property doesn't matter.
uint32_t propIndex;
Rooted<PropMap*> map(cx, obj->shape()->lookup(cx, id, &propIndex));
MOZ_ASSERT(map);
PropertyInfo prop = map->getPropertyInfo(propIndex);
bool wasAccessor = prop.isAccessorProperty();
bool isAccessor = flags.isAccessorProperty();
if (wasAccessor != isAccessor) {
obj->as<GlobalObject>().bumpGenerationCount();
}
}
// Property fuses should also be popped on property changes, as value can
// change via this path.
if (MOZ_UNLIKELY(obj->hasFuseProperty())) {
MaybePopFuses(cx, obj, id);
}
if (MOZ_UNLIKELY(obj->useWatchtowerTestingLog())) {
RootedValue val(cx, IdToValue(id));
if (!AddToWatchtowerLog(cx, "change-prop", obj, val)) {
return false;
}
}
return true;
}
// static
template <AllowGC allowGC>
bool Watchtower::watchPropertyModificationSlow(
JSContext* cx, typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
typename MaybeRooted<PropertyKey, allowGC>::HandleType id) {
MOZ_ASSERT(watchesPropertyModification(obj));
if (MOZ_UNLIKELY(obj->hasFuseProperty())) {
MaybePopFuses(cx, obj, id);
}
// If we cannot GC, we can't manipulate the log, but we need to be able to
// call this in places we cannot GC.
if constexpr (allowGC == AllowGC::CanGC) {
if (MOZ_UNLIKELY(obj->useWatchtowerTestingLog())) {
RootedValue val(cx, IdToValue(id));
if (!AddToWatchtowerLog(cx, "modify-prop", obj, val)) {
return false;
}
}
}
return true;
}
template bool Watchtower::watchPropertyModificationSlow<AllowGC::CanGC>(
JSContext* cx,
typename MaybeRooted<NativeObject*, AllowGC::CanGC>::HandleType obj,
typename MaybeRooted<PropertyKey, AllowGC::CanGC>::HandleType id);
template bool Watchtower::watchPropertyModificationSlow<AllowGC::NoGC>(
JSContext* cx,
typename MaybeRooted<NativeObject*, AllowGC::NoGC>::HandleType obj,
typename MaybeRooted<PropertyKey, AllowGC::NoGC>::HandleType id);
// static
bool Watchtower::watchFreezeOrSealSlow(JSContext* cx,
Handle<NativeObject*> obj) {
MOZ_ASSERT(watchesFreezeOrSeal(obj));
if (MOZ_UNLIKELY(obj->useWatchtowerTestingLog())) {
if (!AddToWatchtowerLog(cx, "freeze-or-seal", obj,
JS::UndefinedHandleValue)) {
return false;
}
}
return true;
}
// static
bool Watchtower::watchObjectSwapSlow(JSContext* cx, HandleObject a,
HandleObject b) {
MOZ_ASSERT(watchesObjectSwap(a, b));
// If we're swapping an object that's used as prototype, we're mutating the
// proto chains of other objects. Treat this as a proto change to ensure we
// invalidate shape teleporting and megamorphic caches.
if (!WatchProtoChangeImpl(cx, a)) {
return false;
}
if (!WatchProtoChangeImpl(cx, b)) {
return false;
}
// Note: we don't invoke the testing callback for swap because the objects may
// not be safe to expose to JS at this point. See bug 1754699.
return true;
}