Never mark free list elements.

runtime/vm/verifier.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/verifier.h"
 
 #include "platform/assert.h"
 #include "vm/dart.h"
 #include "vm/dart_api_state.h"
 #include "vm/freelist.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
 #include "vm/object_set.h"
 #include "vm/raw_object.h"
 #include "vm/stack_frame.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, verify_on_transition, false, "Verify on dart <==> VM.");
 
 
 void VerifyObjectVisitor::VisitObject(RawObject* raw_obj) {
   if (raw_obj->IsHeapObject()) {
-    switch (mark_expectation_) {
-     case kForbidMarked:
+    uword raw_addr = RawObject::ToAddr(raw_obj);
+    if (raw_obj->IsFreeListElement()) {
       if (raw_obj->IsMarked()) {
-        uword raw_addr = RawObject::ToAddr(raw_obj);
-        FATAL1("Marked object encountered %#" Px "\n", raw_addr);
+        FATAL1("Marked free list element encountered %#" Px "\n", raw_addr);
       }
-      break;
-     case kAllowMarked:
-      break;
-     case kRequireMarked:
-      if (!raw_obj->IsMarked()) {
-        uword raw_addr = RawObject::ToAddr(raw_obj);
-        FATAL1("Unmarked object encountered %#" Px "\n", raw_addr);
+    } else {
+      switch (mark_expectation_) {
+       case kForbidMarked:
+        if (raw_obj->IsMarked()) {
+          FATAL1("Marked object encountered %#" Px "\n", raw_addr);
+        }
+        break;
+       case kAllowMarked:
+        break;
+       case kRequireMarked:
+        if (!raw_obj->IsMarked()) {
+          FATAL1("Unmarked object encountered %#" Px "\n", raw_addr);
+        }
+        break;
       }
-      break;
     }
   }
   allocated_set_->Add(raw_obj);
   raw_obj->Validate(isolate());
 }
 
 
 void VerifyPointersVisitor::VisitPointers(RawObject** first, RawObject** last) {
   for (RawObject** current = first; current <= last; current++) {
     VerifiedMemory::Verify(reinterpret_cast<uword>(current), kWordSize);
@@ skipping 27 matching lines @@
                                false,  // skip prologue weak handles
                                StackFrameIterator::kValidateFrames);
   VerifyWeakPointersVisitor weak_visitor(&visitor);
   // Visit weak handles and prologue weak handles.
   isolate->VisitWeakPersistentHandles(&weak_visitor,
                                       true);  // visit prologue weak handles
   delete allocated_set;
 }
 
 }  // namespace dart