Store embed-script flag as metadata into snapshot blob.

src/snapshot-common.cc

 // Copyright 2006-2008 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.
 
 // The common functionality when building with or without snapshots.
 
 #include "src/v8.h"
 
 #include "src/api.h"
 #include "src/base/platform/platform.h"
 #include "src/serialize.h"
 #include "src/snapshot.h"
 
 namespace v8 {
 namespace internal {
 
 bool Snapshot::HaveASnapshotToStartFrom() {
   return SnapshotBlob().data != NULL;
 }
 
 
+#ifdef DEBUG
+bool Snapshot::SnapshotIsValid(v8::StartupData* snapshot_blob) {
+  return !Snapshot::ExtractStartupData(snapshot_blob).is_empty() &&
+         !Snapshot::ExtractContextData(snapshot_blob).is_empty();
+}
+#endif  // DEBUG
+
+
+bool Snapshot::EmbedsScript() {
+  if (!HaveASnapshotToStartFrom()) return false;
+  const v8::StartupData blob = SnapshotBlob();
+  return ExtractMetadata(&blob).embeds_script();
+}
+
+
 bool Snapshot::Initialize(Isolate* isolate) {
   if (!HaveASnapshotToStartFrom()) return false;
   base::ElapsedTimer timer;
   if (FLAG_profile_deserialization) timer.Start();
 
   const v8::StartupData blob = SnapshotBlob();
   Vector<const byte> startup_data = ExtractStartupData(&blob);
   SnapshotData snapshot_data(startup_data);
   Deserializer deserializer(&snapshot_data);
   bool success = isolate->Init(&deserializer);
@@ skipping 15 matching lines @@
   const v8::StartupData blob = SnapshotBlob();
   Vector<const byte> context_data = ExtractContextData(&blob);
   SnapshotData snapshot_data(context_data);
   Deserializer deserializer(&snapshot_data);
 
   MaybeHandle<Object> maybe_context =
       deserializer.DeserializePartial(isolate, outdated_contexts_out);
   Handle<Object> result;
   if (!maybe_context.ToHandle(&result)) return MaybeHandle<Context>();
   CHECK(result->IsContext());
+  // If the snapshot does not contain a custom script, we need to update
+  // the global object for exactly one context.
+  CHECK(EmbedsScript() || (*outdated_contexts_out)->length() == 1);
   if (FLAG_profile_deserialization) {
     double ms = timer.Elapsed().InMillisecondsF();
     int bytes = context_data.length();
     PrintF("[Deserializing context (%d bytes) took %0.3f ms]\n", bytes, ms);
   }
   return Handle<Context>::cast(result);
 }
 
 
 v8::StartupData Snapshot::CreateSnapshotBlob(
     const Vector<const byte> startup_data,
-    const Vector<const byte> context_data) {
+    const Vector<const byte> context_data, Snapshot::Metadata metadata) {
   int startup_length = startup_data.length();
   int context_length = context_data.length();
-  int context_offset = kIntSize + startup_length;
+  int context_offset = ContextOffset(startup_length);
+
   int length = context_offset + context_length;
   char* data = new char[length];
 
-  memcpy(data, &startup_length, kIntSize);
-  memcpy(data + kIntSize, startup_data.begin(), startup_length);
+  memcpy(data + kMetadataOffset, &metadata.RawValue(), kInt32Size);
+  memcpy(data + kStartupLengthOffset, &startup_length, kInt32Size);
+  memcpy(data + kStartupDataOffset, startup_data.begin(), startup_length);
   memcpy(data + context_offset, context_data.begin(), context_length);
   v8::StartupData result = {data, length};
   return result;
 }
 
 
+Snapshot::Metadata Snapshot::ExtractMetadata(const v8::StartupData* data) {
+  uint32_t raw;
+  memcpy(&raw, data->data + kMetadataOffset, kInt32Size);
+  return Metadata(raw);
+}
+
+
 Vector<const byte> Snapshot::ExtractStartupData(const v8::StartupData* data) {
   DCHECK_LT(kIntSize, data->raw_size);
   int startup_length;
-  memcpy(&startup_length, data->data, kIntSize);
+  memcpy(&startup_length, data->data + kStartupLengthOffset, kInt32Size);
   DCHECK_LT(startup_length, data->raw_size);
   const byte* startup_data =
-      reinterpret_cast<const byte*>(data->data + kIntSize);
+      reinterpret_cast<const byte*>(data->data + kStartupDataOffset);
   return Vector<const byte>(startup_data, startup_length);
 }
 
 
 Vector<const byte> Snapshot::ExtractContextData(const v8::StartupData* data) {
   DCHECK_LT(kIntSize, data->raw_size);
   int startup_length;
-  memcpy(&startup_length, data->data, kIntSize);
-  int context_offset = kIntSize + startup_length;
+  memcpy(&startup_length, data->data + kStartupLengthOffset, kIntSize);
+  int context_offset = ContextOffset(startup_length);
   const byte* context_data =
       reinterpret_cast<const byte*>(data->data + context_offset);
   DCHECK_LT(context_offset, data->raw_size);
   int context_length = data->raw_size - context_offset;
   return Vector<const byte>(context_data, context_length);
 }
 } }  // namespace v8::internal