tor-browser

Watchtower.h (7264B)

---

/* -*- 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/. */

#ifndef vm_Watchtower_h
#define vm_Watchtower_h

#include "js/TypeDecls.h"
#include "vm/NativeObject.h"

namespace js {

enum class SetSlotOptimizable { Yes, No, NotYet };

// [SMDOC] Watchtower
//
// Watchtower is a framework to hook into changes to certain objects. This gives
// us the ability to, for instance, invalidate caches or purge Warp code on
// object layout changes.
//
// Watchtower is only used for objects with certain ObjectFlags set on the
// Shape. This minimizes performance overhead for most objects.
//
// We currently use Watchtower for:
//
// - Invalidating the shape teleporting optimization. See the "Shape Teleporting
//   Optimization" SMDOC comment in CacheIR.cpp.
//
// - Invalidating the MegamorphicCache, a property lookup cache for megamorphic
//   property accesses. See the SMDOC comment in vm/Caches.h.
//
// There's also a testing mechanism that lets us write tests for Watchtower
// hooks. See setWatchtowerCallback and addWatchtowerTarget defined in
// TestingFunctions.cpp.
class Watchtower {
 static bool watchPropertyAddSlow(JSContext* cx, Handle<NativeObject*> obj,
                                  HandleId id);
 static bool watchPropertyRemoveSlow(JSContext* cx, Handle<NativeObject*> obj,
                                     HandleId id, PropertyInfo propInfo,
                                     bool* wasTrackedObjectFuseProp);
 static bool watchPropertyFlagsChangeSlow(JSContext* cx,
                                          Handle<NativeObject*> obj,
                                          HandleId id, PropertyInfo propInfo,
                                          PropertyFlags newFlags);
 template <AllowGC allowGC>
 static void watchPropertyValueChangeSlow(
     JSContext* cx,
     typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
     typename MaybeRooted<PropertyKey, allowGC>::HandleType id,
     typename MaybeRooted<Value, allowGC>::HandleType value,
     PropertyInfo propInfo);
 static bool watchFreezeOrSealSlow(JSContext* cx, Handle<NativeObject*> obj,
                                   IntegrityLevel level);
 static bool watchProtoChangeSlow(JSContext* cx, HandleObject obj);
 static bool watchObjectSwapSlow(JSContext* cx, HandleObject a,
                                 HandleObject b);
 static SetSlotOptimizable canOptimizeSetSlotSlow(JSContext* cx,
                                                  NativeObject* obj,
                                                  PropertyInfo prop);

public:
 static bool watchesPropertyAdd(NativeObject* obj) {
   return obj->hasAnyFlag(
       {ObjectFlag::IsUsedAsPrototype, ObjectFlag::UseWatchtowerTestingLog});
 }
 static bool watchesPropertyRemove(NativeObject* obj) {
   return obj->hasAnyFlag(
       {ObjectFlag::IsUsedAsPrototype, ObjectFlag::GenerationCountedGlobal,
        ObjectFlag::UseWatchtowerTestingLog, ObjectFlag::HasRealmFuseProperty,
        ObjectFlag::HasObjectFuse});
 }
 static bool watchesPropertyFlagsChange(NativeObject* obj) {
   return obj->hasAnyFlag({ObjectFlag::IsUsedAsPrototype,
                           ObjectFlag::GenerationCountedGlobal,
                           ObjectFlag::UseWatchtowerTestingLog});
 }
 static bool watchesPropertyValueChange(NativeObject* obj) {
   return obj->hasAnyFlag({ObjectFlag::HasRealmFuseProperty,
                           ObjectFlag::UseWatchtowerTestingLog,
                           ObjectFlag::HasObjectFuse});
 }
 static bool watchesFreezeOrSeal(NativeObject* obj) {
   return obj->hasAnyFlag(
       {ObjectFlag::IsUsedAsPrototype, ObjectFlag::UseWatchtowerTestingLog});
 }
 static bool watchesProtoChange(JSObject* obj) {
   return obj->hasAnyFlag(
       {ObjectFlag::IsUsedAsPrototype, ObjectFlag::UseWatchtowerTestingLog});
 }
 static bool watchesObjectSwap(JSObject* a, JSObject* b) {
   auto watches = [](JSObject* obj) {
     return obj->hasAnyFlag({ObjectFlag::IsUsedAsPrototype,
                             ObjectFlag::UseWatchtowerTestingLog,
                             ObjectFlag::HasObjectFuse});
   };
   return watches(a) || watches(b);
 }
 static SetSlotOptimizable canOptimizeSetSlot(JSContext* cx, NativeObject* obj,
                                              PropertyInfo prop) {
   if (obj->hasAnyFlag({ObjectFlag::HasRealmFuseProperty,
                        ObjectFlag::UseWatchtowerTestingLog})) {
     return SetSlotOptimizable::No;
   }
   if (!obj->hasObjectFuse()) {
     return SetSlotOptimizable::Yes;
   }
   return canOptimizeSetSlotSlow(cx, obj, prop);
 }

 static bool watchPropertyAdd(JSContext* cx, Handle<NativeObject*> obj,
                              HandleId id) {
   if (MOZ_LIKELY(!watchesPropertyAdd(obj))) {
     return true;
   }
   return watchPropertyAddSlow(cx, obj, id);
 }
 static bool watchPropertyRemove(JSContext* cx, Handle<NativeObject*> obj,
                                 HandleId id, PropertyInfo propInfo,
                                 bool* wasTrackedObjectFuseProp) {
   MOZ_ASSERT(!*wasTrackedObjectFuseProp);
   if (MOZ_LIKELY(!watchesPropertyRemove(obj))) {
     return true;
   }
   return watchPropertyRemoveSlow(cx, obj, id, propInfo,
                                  wasTrackedObjectFuseProp);
 }
 static bool watchPropertyFlagsChange(JSContext* cx, Handle<NativeObject*> obj,
                                      HandleId id, PropertyInfo propInfo,
                                      PropertyFlags newFlags) {
   if (MOZ_LIKELY(!watchesPropertyFlagsChange(obj))) {
     return true;
   }
   return watchPropertyFlagsChangeSlow(cx, obj, id, propInfo, newFlags);
 }

 // Note: We can only watch property value changes for regular object slots
 // with an id, not reserved slots.
 template <AllowGC allowGC>
 static void watchPropertyValueChange(
     JSContext* cx,
     typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
     typename MaybeRooted<PropertyKey, allowGC>::HandleType id,
     typename MaybeRooted<Value, allowGC>::HandleType value,
     PropertyInfo propInfo) {
   if (MOZ_LIKELY(!watchesPropertyValueChange(obj))) {
     return;
   }
   watchPropertyValueChangeSlow<allowGC>(cx, obj, id, value, propInfo);
 }
 static bool watchFreezeOrSeal(JSContext* cx, Handle<NativeObject*> obj,
                               IntegrityLevel level) {
   if (MOZ_LIKELY(!watchesFreezeOrSeal(obj))) {
     return true;
   }
   return watchFreezeOrSealSlow(cx, obj, level);
 }
 static bool watchProtoChange(JSContext* cx, HandleObject obj) {
   if (MOZ_LIKELY(!watchesProtoChange(obj))) {
     return true;
   }
   return watchProtoChangeSlow(cx, obj);
 }

 static bool watchObjectSwap(JSContext* cx, HandleObject a, HandleObject b) {
   if (MOZ_LIKELY(!watchesObjectSwap(a, b))) {
     return true;
   }
   return watchObjectSwapSlow(cx, a, b);
 }
};

}  // namespace js

#endif /* vm_Watchtower_h */