Deletion barrier preparation: validate overwritten references.

runtime/vm/snapshot.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/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/exceptions.h"
@@ skipping 807 matching lines @@
   ASSERT(IsObjectStoreClassId(class_id));
   return class_id;
 }
 
 
 RawObject* SnapshotReader::AllocateUninitialized(intptr_t class_id,
                                                  intptr_t size) {
   ASSERT(isolate()->no_gc_scope_depth() != 0);
   ASSERT(Utils::IsAligned(size, kObjectAlignment));
 
+  // Allocate memory where all words look like smis. This is currently
+  // only needed for DEBUG-mode validation in StorePointer/StoreSmi, but will
+  // be essential with the upcoming deletion barrier.
   uword address =
-      old_space()->TryAllocateDataBumpLocked(size, PageSpace::kForceGrowth);
+      old_space()->TryAllocateSmiInitializedLocked(size,
+                                                   PageSpace::kForceGrowth);
   if (address == 0) {
     // Use the preallocated out of memory exception to avoid calling
     // into dart code or allocating any code.
     // We do a longjmp at this point to unwind out of the entire
     // read part and return the error object back.
     const UnhandledException& error = UnhandledException::Handle(
         object_store()->preallocated_unhandled_exception());
     Isolate::Current()->long_jump_base()->Jump(1, error);
   }
-#if defined(DEBUG)
-  // Zap the uninitialized memory area.
-  uword current = address;
-  uword end = address + size;
-  while (current < end) {
-    *reinterpret_cast<intptr_t*>(current) = kZapUninitializedWord;
-    current += kWordSize;
-  }
-#endif  // defined(DBEUG)
-  // Make sure to initialize the last word, as this can be left untouched in
-  // case the object deserialized has an alignment tail.
-  *reinterpret_cast<RawObject**>(address + size - kWordSize) = Object::null();
   VerifiedMemory::Accept(address, size);
 
   RawObject* raw_obj = reinterpret_cast<RawObject*>(address + kHeapObjectTag);
   uword tags = 0;
   ASSERT(class_id != kIllegalCid);
   tags = RawObject::ClassIdTag::update(class_id, tags);
   tags = RawObject::SizeTag::update(size, tags);
   raw_obj->ptr()->tags_ = tags;
   return raw_obj;
 }
@@ skipping 914 matching lines @@
     NoGCScope no_gc;
     WriteObject(obj.raw());
     UnmarkAll();
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart