[Oilpan] Add use-after-free detector in Member<>

third_party/WebKit/Source/platform/heap/Heap.h

Index: third_party/WebKit/Source/platform/heap/Heap.h
diff --git a/third_party/WebKit/Source/platform/heap/Heap.h b/third_party/WebKit/Source/platform/heap/Heap.h
index 67a8bc873ef643166d19459cecc0c07fab89dab3..73a9105140699ecef8df2c624d1e3b37bac6a0e7 100644
--- a/third_party/WebKit/Source/platform/heap/Heap.h
+++ b/third_party/WebKit/Source/platform/heap/Heap.h
@@ -47,6 +47,8 @@ template<typename T> class Member;
 template<typename T> class WeakMember;
 template<typename T> class UntracedMember;
 
+// TODO(peria): Refactor following two sets of template.
+
 template<typename T, bool = NeedsAdjustAndMark<T>::value> class ObjectAliveTrait;
 
 template<typename T>
@@ -69,6 +71,38 @@ public:
     }
 };
 
+template<typename T, bool = IsGarbageCollectedMixin<T>::value> class GarbageCollectedMixinTrait;
+
+template<typename T>
+class GarbageCollectedMixinTrait<T, true> {

[haraken, 2015/11/11 10:03:16]

I'd rename this to HeapObjectHeaderTrait since this is a Trait for getting a
HeapObjectHeader, regardless of whether T is GarbageCollected or
GarbageCollectedMixin.

[peria, 2015/11/12 14:38:41]

Done.

+public:
+    static HeapObjectHeader* heapObjectHeader(T* obj)
+    {

[haraken, 2015/11/11 10:03:16]

Add ASSERT(!ThreadState::current()->isConstructingGCMixin()).

[peria, 2015/11/12 14:38:42]

This method may be called in Member<>::get(), and
it can happen in a constructor of another GCMixin class.

[haraken, 2015/11/16 06:20:30]

Isn't it unsafe? If obj->heapObjectHeader() is called while constructing a mixin
class, the behavior would be undefined.

My point is that HeapObjectHeader::heapObjectHeader() should not be called when
ThreadState::current()->isConstructingGCMixin() is true.

[peria, 2015/11/16 07:04:42]

If an object which is being constructed is an argument of this call,
it is unsafe and must be avoided.
But it doesn't mean to prevent to call this method while
ThreadState::current()->isConstructingGCMixin() is true.
In following code, we should be able to call
HeapObjectHeaderTrait<X>::heapObjectHeader(x) in the constructor of A.


struct X : public GarbageCollectedMixin { ... };
struct Y : public GarbageCollected<Y>, public X { ... };
struct A : public GarbageCollectedMixin {
  A() : x(new Y) {
    ASSERT(HeapObjectHeadertrait<X>::heapObjectHeader(x));
  }
  Member x;
};
struct B : public GarbageCollected<B>, public A { ... };

+        return obj->heapObjectHeader();
+    }
+    static uint32_t gcGeneration(T* obj)
+    {
+        // While constructing GarbageCollectedMixin classes, we skip looking
+        // for gcGeneration, because the object may not be fully allocated.
+        if (ThreadState::current()->isConstructingGCMixin())
+            return 0;
+        return heapObjectHeader(obj)->gcGeneration();
+    }
+};
+
+template<typename T>
+class GarbageCollectedMixinTrait<T, false> {
+public:
+    static HeapObjectHeader* heapObjectHeader(T* obj)
+    {

[haraken, 2015/11/11 10:03:16]

Add ASSERT(!ThreadState::current()->isConstructingGCMixin()).

[peria, 2015/11/12 14:38:42]

ditto.

+        return HeapObjectHeader::fromPayload(obj);
+    }
+    static uint32_t gcGeneration(T* obj)
+    {
+        return heapObjectHeader(obj)->gcGeneration();
+    }
+};
+
 class PLATFORM_EXPORT Heap {
 public:
     static void init();
@@ -96,17 +130,17 @@ public:
     template<typename T>
     static inline bool isHeapObjectAlive(const Member<T>& member)
     {
-        return isHeapObjectAlive(member.get());
+        return isHeapObjectAlive(member.unsafeGet());
     }
     template<typename T>
     static inline bool isHeapObjectAlive(const WeakMember<T>& member)
     {
-        return isHeapObjectAlive(member.get());
+        return isHeapObjectAlive(member.unsafeGet());
     }
     template<typename T>
     static inline bool isHeapObjectAlive(const UntracedMember<T>& member)
     {
-        return isHeapObjectAlive(member.get());
+        return isHeapObjectAlive(member.unsafeGet());
     }
     template<typename T>
     static inline bool isHeapObjectAlive(const RawPtr<T>& ptr)
@@ -260,7 +294,7 @@ public:
     static void reportMemoryUsageForTracing();
 
 #if ENABLE(ASSERT)
-    static uint16_t gcGeneration() { return s_gcGeneration; }
+    static uint32_t gcGeneration() { return s_gcGeneration; }
 #endif
 
 private:
@@ -309,7 +343,7 @@ private:
     static size_t s_partitionAllocSizeAtLastGC;
     static double s_estimatedMarkingTimePerByte;
 #if ENABLE(ASSERT)
-    static uint16_t s_gcGeneration;
+    static uint32_t s_gcGeneration;
 #endif
 
     friend class ThreadState;