SSL Watchtower.h

/* 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 SetSlotOptimizable canOptimizeSetSlotSlow(JSContext* cx,
                                                   NativeObject* obj,
                                                   PropertyKey key,
                                                   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 SetSlotOptimizable canOptimizeSetSlot(JSContext* cx, NativeObject* obj,
                                               PropertyKey key,
                                               PropertyInfo prop) {
    if (obj->hasAnyFlag({ObjectFlag::HasRealmFuseProperty,
                         ObjectFlag::UseWatchtowerTestingLog})) {
      return SetSlotOptimizable::No;
    }
    if (!obj->hasObjectFuse()) {
      return SetSlotOptimizable::Yes;
    }
    return canOptimizeSetSlotSlow(cx, obj, key, 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);
  }
};

}  // namespace js

#endif /* vm_Watchtower_h */