179405 2017-11-07 18:00:20 -0800 Avoid using reinterpret_cast in WeakPtr downcasting 2017-11-07 18:00:56 -0800 1 1 1 Unclassified WebKit Web Template Framework WebKit Nightly Build Unspecified Unspecified NEW P2 Normal --- 1 jiewen_tan webkit-unassigned cdumez ggaren jiewen_tan koivisto rniwa oldest_to_newest 1369294 0 jiewen_tan 2017-11-07 18:00:20 -0800 We should probably avoid using reinterpret_cast in WeakPtr downcasting as it might point to a wrong pointer if multiple inheritance is involved. Examples: class Base { public: virtual ~Base() { } int foo() { return 0; } auto& weakPtrFactory() { return m_weakPtrFactory; } private: WeakPtrFactory<Base> m_weakPtrFactory; }; class ExtraBase { public: virtual ~ExtraBase() { } int someExtraData { 1 }; }; class Multi : public ExtraBase, public Base { public: int foo() { return 1; } }; TEST(WTF_WeakPtr, MultiInheritance) { Multi object; Multi* multiPtr = &object; Base* basePtr = static_cast<Base*>(&object); EXPECT_NE((void*)basePtr, (void*)multiPtr); WeakPtr<Base> baseWeakPtr = object.weakPtrFactory().createWeakPtr(object); WeakPtr<Multi> multiWeakPtr = makeWeakPtr(object); EXPECT_NE((void*)baseWeakPtr.get(), (void*)multiWeakPtr.get()); } One can copy and paste the above example into API test of WeakPtr and run the test. The result is: jwtan$ run-api-tests WTF_WeakPtr.MultiInheritance Running build-api-tests FAIL WTF_WeakPtr.MultiInheritance /Users/jwtan/Documents/Source/OpenSource/Tools/TestWebKitAPI/Tests/WTF/WeakPtr.cpp:280 Expected: ((void*)baseWeakPtr.get()) != ((void*)multiWeakPtr.get()), actual: 0x7ffee36e7218 vs 0x7ffee36e7218 Tests that failed: WTF_WeakPtr.MultiInheritance