Deletion barrier preparation: validate overwritten references.

runtime/vm/raw_object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/raw_object.h"
 
 #include "vm/class_table.h"
 #include "vm/dart.h"
 #include "vm/freelist.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
 #include "vm/visitor.h"
 
 
 namespace dart {
 
+#if defined(DEBUG)
+DEFINE_FLAG(bool, validate_overwrite, true, "Verify overwritten fields.");
+#endif  // DEBUG
 
 const intptr_t RawPcDescriptors::kFullRecSize =
     sizeof(RawPcDescriptors::PcDescriptorRec);
 const intptr_t RawPcDescriptors::kCompressedRecSize =
     sizeof(RawPcDescriptors::CompressedPcDescriptorRec);
 
 bool RawObject::IsVMHeapObject() const {
   return Dart::vm_isolate()->heap()->Contains(ToAddr(this));
 }
 
 
 void RawObject::Validate(Isolate* isolate) const {
   if (Object::void_class_ == reinterpret_cast<RawClass*>(kHeapObjectTag)) {
     // Validation relies on properly initialized class classes. Skip if the
     // VM is still being initialized.
     return;
   }
   // All Smi values are valid.
   if (!IsHeapObject()) {
     return;
   }
+  // Slightly more readable than a segfault.
+  if (this == reinterpret_cast<RawObject*>(kHeapObjectTag)) {
+    FATAL("RAW_NULL encountered");
+  }
   // Validate that the tags_ field is sensible.
   uword tags = ptr()->tags_;
   intptr_t reserved = ReservedBits::decode(tags);
   if (reserved != 0) {
     FATAL1("Invalid tags field encountered %#" Px "\n", tags);
   }
   intptr_t class_id = ClassIdTag::decode(tags);
   if (!isolate->class_table()->IsValidIndex(class_id)) {
     FATAL1("Invalid class id encountered %" Pd "\n", class_id);
   }
+  if ((class_id == kNullCid) &&
+      (isolate->class_table()->At(class_id) == NULL)) {
+    // Null class not yet initialized; skip.
+    return;
+  }
   intptr_t size = SizeTag::decode(tags);
   if (size != 0 && size != SizeFromClass()) {
     FATAL1("Inconsistent class size encountered %" Pd "\n", size);
   }
 }
 
 
 intptr_t RawObject::SizeFromClass() const {
   Isolate* isolate = Isolate::Current();
   NoHandleScope no_handles(isolate);
@@ skipping 135 matching lines @@
     }
   }
   ASSERT(instance_size != 0);
   uword tags = ptr()->tags_;
   ASSERT((instance_size == SizeTag::decode(tags)) ||
          (SizeTag::decode(tags) == 0));
   return instance_size;
 }
 
 
+#if defined(DEBUG)
+void RawObject::ValidateOverwrittenPointer(RawObject* raw) {
+  if (FLAG_validate_overwrite) {
+    raw->Validate(Isolate::Current());
+  }
+}
+
+
+void RawObject::ValidateOverwrittenSmi(RawSmi* raw) {
+  if (FLAG_validate_overwrite && raw->IsHeapObject() && raw != Object::null()) {
+    FATAL1("Expected smi/null, found: %" Px "\n", reinterpret_cast<uword>(raw));
+  }
+}
+#endif  // DEBUG
+
+
 intptr_t RawObject::VisitPointers(ObjectPointerVisitor* visitor) {
   intptr_t size = 0;
   NoHandleScope no_handles(visitor->isolate());
 
   // Only reasonable to be called on heap objects.
   ASSERT(IsHeapObject());
 
   // Read the necessary data out of the class before visting the class itself.
   intptr_t class_id = GetClassId();
 
@@ skipping 670 matching lines @@
 intptr_t RawUserTag::VisitUserTagPointers(
     RawUserTag* raw_obj, ObjectPointerVisitor* visitor) {
   // Make sure that we got here with the tagged pointer as this.
   ASSERT(raw_obj->IsHeapObject());
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());
   return UserTag::InstanceSize();
 }
 
 
 }  // namespace dart