[serializer] Ensure immortal immovable roots are deserialized correctly.

src/snapshot/serialize.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/snapshot/serialize.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/platform/platform.h"
 #include "src/bootstrapper.h"
@@ skipping 1697 matching lines @@
     // serializing the canonical interpreter-entry-trampoline builtin.
     if (code->kind() == Code::FUNCTION ||
         (!serializing_builtins_ && code->is_interpreter_entry_trampoline())) {
       obj = isolate()->builtins()->builtin(Builtins::kCompileLazy);
     }
   } else if (obj->IsBytecodeArray()) {
     obj = isolate()->heap()->undefined_value();
   }
 
   int root_index = root_index_map_.Lookup(obj);
+  bool is_immortal_immovable_root = false;
   // We can only encode roots as such if it has already been serialized.
   // That applies to root indices below the wave front.
-  if (root_index != RootIndexMap::kInvalidRootIndex &&
-      root_index < root_index_wave_front_) {
-    PutRoot(root_index, obj, how_to_code, where_to_point, skip);
-    return;
+  if (root_index != RootIndexMap::kInvalidRootIndex) {
+    if (root_index < root_index_wave_front_) {
+      PutRoot(root_index, obj, how_to_code, where_to_point, skip);
+      return;
+    } else {
+      is_immortal_immovable_root = Heap::RootIsImmortalImmovable(root_index);
+    }
   }
 
   if (SerializeKnownObject(obj, how_to_code, where_to_point, skip)) return;
 
   FlushSkip(skip);
 
   // Object has not yet been serialized.  Serialize it here.
   ObjectSerializer object_serializer(this, obj, sink_, how_to_code,
                                      where_to_point);
   object_serializer.Serialize();
+
+  if (is_immortal_immovable_root) {
+    // Make sure that the immortal immovable root has been included in the first
+    // chunk of its reserved space , so that it is deserialized onto the first

[Michael Starzinger, 2016/02/05 14:47:59]

nit: Spurious white-space before comma.

+    // page of its space and stays immortal immovable.
+    BackReference ref = back_reference_map_.Lookup(obj);
+    CHECK(ref.is_valid() && ref.chunk_index() == 0);
+  }
 }
 
 
 void StartupSerializer::SerializeWeakReferencesAndDeferred() {
   // This phase comes right after the serialization (of the snapshot).
   // After we have done the partial serialization the partial snapshot cache
   // will contain some references needed to decode the partial snapshot.  We
   // add one entry with 'undefined' which is the sentinel that the deserializer
   // uses to know it is done deserializing the array.
   Object* undefined = isolate()->heap()->undefined_value();
@@ skipping 1103 matching lines @@
   SerializedCodeData* scd = new SerializedCodeData(cached_data);
   SanityCheckResult r = scd->SanityCheck(isolate, source);
   if (r == CHECK_SUCCESS) return scd;
   cached_data->Reject();
   source->GetIsolate()->counters()->code_cache_reject_reason()->AddSample(r);
   delete scd;
   return NULL;
 }
 }  // namespace internal
 }  // namespace v8