Changeset 154366 in webkit for trunk/Source/JavaScriptCore/runtime/JSObject.cpp

Timestamp:

Aug 20, 2013, 3:17:29 PM (12 years ago)

Author:

[email protected]

Message:

<​https://webkit.org/b/120079> Flattening a dictionary can cause CopiedSpace corruption

Reviewed by Oliver Hunt.

When we flatten an object in dictionary mode, we compact its properties. If the object
had out-of-line storage in the form of a Butterfly prior to this compaction, and after
compaction its properties fit inline, the object's Structure "forgets" that the object
has a non-zero Butterfly pointer. During GC, we check the Butterfly and reportLiveBytes
with bytes = 0, which causes all sorts of badness in CopiedSpace.

Instead, after we flatten a dictionary, if properties fit inline we should clear the
Butterfly pointer so that the GC doesn't get confused later.

This patch does this clearing, and it also adds JSObject::checkStructure, which overrides
JSCell::checkStructure to add an ASSERT that makes sure that the Structure being assigned
agrees with the whether or not the object has a Butterfly. Also added an ASSERT to check
that the number of bytes reported to SlotVisitor::copyLater is non-zero.

• heap/SlotVisitorInlines.h:

(JSC::SlotVisitor::copyLater):

• runtime/JSObject.cpp:

(JSC::JSObject::notifyPresenceOfIndexedAccessors):
(JSC::JSObject::convertUndecidedToInt32):
(JSC::JSObject::convertUndecidedToDouble):
(JSC::JSObject::convertUndecidedToContiguous):
(JSC::JSObject::convertInt32ToDouble):
(JSC::JSObject::convertInt32ToContiguous):
(JSC::JSObject::genericConvertDoubleToContiguous):
(JSC::JSObject::switchToSlowPutArrayStorage):
(JSC::JSObject::setPrototype):
(JSC::JSObject::putDirectAccessor):
(JSC::JSObject::seal):
(JSC::JSObject::freeze):
(JSC::JSObject::preventExtensions):
(JSC::JSObject::reifyStaticFunctionsForDelete):
(JSC::JSObject::removeDirect):

• runtime/JSObject.h:

(JSC::JSObject::setButterfly):
(JSC::JSObject::putDirectInternal):
(JSC::JSObject::setStructure):
(JSC::JSObject::setStructureAndReallocateStorageIfNecessary):

• runtime/Structure.cpp:

(JSC::Structure::flattenDictionaryStructure):

File:

• trunk/Source/JavaScriptCore/runtime/JSObject.cpp (modified) (15 diffs)

trunk/Source/JavaScriptCore/runtime/JSObject.cpp

@@ -584 +584 @@
         return;
     
-    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AddIndexedAccessors));
+    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AddIndexedAccessors), m_butterfly);
     
     if (!vm.prototypeMap.isPrototype(this))
@@ -670 +670 @@
 {
     ASSERT(hasUndecided(structure()->indexingType()));
-    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateInt32));
+    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateInt32), m_butterfly);
     return m_butterfly->contiguousInt32();
 }
@@ -681 +681 @@
         m_butterfly->contiguousDouble()[i] = QNaN;
     
-    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateDouble));
+    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateDouble), m_butterfly);
     return m_butterfly->contiguousDouble();
 }
@@ -688 +688 @@
 {
     ASSERT(hasUndecided(structure()->indexingType()));
-    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateContiguous));
+    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateContiguous), m_butterfly);
     return m_butterfly->contiguous();
 }
@@ -754 +754 @@
     }
     
-    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateDouble));
+    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateDouble), m_butterfly);
     return m_butterfly->contiguousDouble();
 }
@@ -762 +762 @@
     ASSERT(hasInt32(structure()->indexingType()));
     
-    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateContiguous));
+    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateContiguous), m_butterfly);
     return m_butterfly->contiguous();
 }
@@ -820 +820 @@
     }
     
-    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateContiguous));
+    setStructure(vm, Structure::nonPropertyTransition(vm, structure(), AllocateContiguous), m_butterfly);
     return m_butterfly->contiguous();
 }
@@ -1118 +1118 @@
     case ArrayWithArrayStorage: {
         Structure* newStructure = Structure::nonPropertyTransition(vm, structure(), SwitchToSlowPutArrayStorage);
-        setStructure(vm, newStructure);
+        setStructure(vm, newStructure, m_butterfly);
         break;
     }
@@ -1142 +1142 @@
     
     Structure* newStructure = Structure::changePrototypeTransition(vm, structure(), prototype);
-    setStructure(vm, newStructure);
+    setStructure(vm, newStructure, m_butterfly);
     
     if (!newStructure->anyObjectInChainMayInterceptIndexedAccesses())
@@ -1199 +1199 @@
     // if we override an existing non-getter or non-setter.
     if (slot.type() != PutPropertySlot::NewProperty)
-        setStructure(vm, Structure::attributeChangeTransition(vm, structure(), propertyName, attributes));
+        setStructure(vm, Structure::attributeChangeTransition(vm, structure(), propertyName, attributes), m_butterfly);
 
     if (attributes & ReadOnly)
@@ -1556 +1556 @@
         return;
     preventExtensions(vm);
-    setStructure(vm, Structure::sealTransition(vm, structure()));
+    setStructure(vm, Structure::sealTransition(vm, structure()), m_butterfly);
 }
 
@@ -1564 +1564 @@
         return;
     preventExtensions(vm);
-    setStructure(vm, Structure::freezeTransition(vm, structure()));
+    setStructure(vm, Structure::freezeTransition(vm, structure()), m_butterfly);
 }
 
@@ -1571 +1571 @@
     enterDictionaryIndexingMode(vm);
     if (isExtensible())
-        setStructure(vm, Structure::preventExtensionsTransition(vm, structure()));
+        setStructure(vm, Structure::preventExtensionsTransition(vm, structure()), m_butterfly);
 }
 
@@ -1589 +1589 @@
 
     if (!structure()->isUncacheableDictionary())
-        setStructure(vm, Structure::toUncacheableDictionaryTransition(vm, structure()));
+        setStructure(vm, Structure::toUncacheableDictionaryTransition(vm, structure()), m_butterfly);
 
     for (const ClassInfo* info = classInfo(); info; info = info->parentClass) {
@@ -1619 +1619 @@
     }
 
-    setStructure(vm, Structure::removePropertyTransition(vm, structure(), propertyName, offset));
+    setStructure(vm, Structure::removePropertyTransition(vm, structure(), propertyName, offset), m_butterfly);
     if (offset == invalidOffset)
         return false;