[serializer] split up src/snapshot/serialize.*

src/snapshot/serializer.cc

+// Copyright 2016 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/serializer.h"
+
+#include "src/macro-assembler.h"
+#include "src/snapshot/natives.h"
+
+namespace v8 {
+namespace internal {
+
+Serializer::Serializer(Isolate* isolate, SnapshotByteSink* sink)
+    : isolate_(isolate),
+      sink_(sink),
+      external_reference_encoder_(isolate),
+      root_index_map_(isolate),
+      recursion_depth_(0),
+      code_address_map_(NULL),
+      large_objects_total_size_(0),
+      seen_large_objects_index_(0) {
+  // The serializer is meant to be used only to generate initial heap images
+  // from a context in which there is only one isolate.
+  for (int i = 0; i < kNumberOfPreallocatedSpaces; i++) {
+    pending_chunk_[i] = 0;
+    max_chunk_size_[i] = static_cast<uint32_t>(
+        MemoryAllocator::PageAreaSize(static_cast<AllocationSpace>(i)));
+  }
+
+#ifdef OBJECT_PRINT
+  if (FLAG_serialization_statistics) {
+    instance_type_count_ = NewArray<int>(kInstanceTypes);
+    instance_type_size_ = NewArray<size_t>(kInstanceTypes);
+    for (int i = 0; i < kInstanceTypes; i++) {
+      instance_type_count_[i] = 0;
+      instance_type_size_[i] = 0;
+    }
+  } else {
+    instance_type_count_ = NULL;
+    instance_type_size_ = NULL;
+  }
+#endif  // OBJECT_PRINT
+}
+
+Serializer::~Serializer() {
+  if (code_address_map_ != NULL) delete code_address_map_;
+#ifdef OBJECT_PRINT
+  if (instance_type_count_ != NULL) {
+    DeleteArray(instance_type_count_);
+    DeleteArray(instance_type_size_);
+  }
+#endif  // OBJECT_PRINT
+}
+
+#ifdef OBJECT_PRINT
+void Serializer::CountInstanceType(Map* map, int size) {
+  int instance_type = map->instance_type();
+  instance_type_count_[instance_type]++;
+  instance_type_size_[instance_type] += size;
+}
+#endif  // OBJECT_PRINT
+
+void Serializer::OutputStatistics(const char* name) {
+  if (!FLAG_serialization_statistics) return;
+  PrintF("%s:\n", name);
+  PrintF("  Spaces (bytes):\n");
+  for (int space = 0; space < kNumberOfSpaces; space++) {
+    PrintF("%16s", AllocationSpaceName(static_cast<AllocationSpace>(space)));
+  }
+  PrintF("\n");
+  for (int space = 0; space < kNumberOfPreallocatedSpaces; space++) {
+    size_t s = pending_chunk_[space];
+    for (uint32_t chunk_size : completed_chunks_[space]) s += chunk_size;
+    PrintF("%16" V8_PTR_PREFIX "d", s);
+  }
+  PrintF("%16d\n", large_objects_total_size_);
+#ifdef OBJECT_PRINT
+  PrintF("  Instance types (count and bytes):\n");
+#define PRINT_INSTANCE_TYPE(Name)                                          \
+  if (instance_type_count_[Name]) {                                        \
+    PrintF("%10d %10" V8_PTR_PREFIX "d  %s\n", instance_type_count_[Name], \
+           instance_type_size_[Name], #Name);                              \
+  }
+  INSTANCE_TYPE_LIST(PRINT_INSTANCE_TYPE)
+#undef PRINT_INSTANCE_TYPE
+  PrintF("\n");
+#endif  // OBJECT_PRINT
+}
+
+void Serializer::SerializeDeferredObjects() {
+  while (deferred_objects_.length() > 0) {
+    HeapObject* obj = deferred_objects_.RemoveLast();
+    ObjectSerializer obj_serializer(this, obj, sink_, kPlain, kStartOfObject);
+    obj_serializer.SerializeDeferred();
+  }
+  sink_->Put(kSynchronize, "Finished with deferred objects");
+}
+
+bool Serializer::ShouldBeSkipped(Object** current) {
+  Object** roots = isolate()->heap()->roots_array_start();
+  return current == &roots[Heap::kStoreBufferTopRootIndex] ||
+         current == &roots[Heap::kStackLimitRootIndex] ||
+         current == &roots[Heap::kRealStackLimitRootIndex];
+}
+
+void Serializer::VisitPointers(Object** start, Object** end) {
+  for (Object** current = start; current < end; current++) {
+    if ((*current)->IsSmi()) {
+      sink_->Put(kOnePointerRawData, "Smi");
+      for (int i = 0; i < kPointerSize; i++) {
+        sink_->Put(reinterpret_cast<byte*>(current)[i], "Byte");
+      }
+    } else {
+      SerializeObject(HeapObject::cast(*current), kPlain, kStartOfObject, 0);
+    }
+  }
+}
+
+void Serializer::EncodeReservations(
+    List<SerializedData::Reservation>* out) const {
+  for (int i = 0; i < kNumberOfPreallocatedSpaces; i++) {
+    for (int j = 0; j < completed_chunks_[i].length(); j++) {
+      out->Add(SerializedData::Reservation(completed_chunks_[i][j]));
+    }
+
+    if (pending_chunk_[i] > 0 || completed_chunks_[i].length() == 0) {
+      out->Add(SerializedData::Reservation(pending_chunk_[i]));
+    }
+    out->last().mark_as_last();
+  }
+
+  out->Add(SerializedData::Reservation(large_objects_total_size_));
+  out->last().mark_as_last();
+}
+
+#ifdef DEBUG
+bool Serializer::BackReferenceIsAlreadyAllocated(BackReference reference) {
+  DCHECK(reference.is_valid());
+  DCHECK(!reference.is_source());
+  DCHECK(!reference.is_global_proxy());
+  AllocationSpace space = reference.space();
+  int chunk_index = reference.chunk_index();
+  if (space == LO_SPACE) {
+    return chunk_index == 0 &&
+           reference.large_object_index() < seen_large_objects_index_;
+  } else if (chunk_index == completed_chunks_[space].length()) {
+    return reference.chunk_offset() < pending_chunk_[space];
+  } else {
+    return chunk_index < completed_chunks_[space].length() &&
+           reference.chunk_offset() < completed_chunks_[space][chunk_index];
+  }
+}
+#endif  // DEBUG
+
+bool Serializer::SerializeKnownObject(HeapObject* obj, HowToCode how_to_code,
+                                      WhereToPoint where_to_point, int skip) {
+  if (how_to_code == kPlain && where_to_point == kStartOfObject) {
+    // Encode a reference to a hot object by its index in the working set.
+    int index = hot_objects_.Find(obj);
+    if (index != HotObjectsList::kNotFound) {
+      DCHECK(index >= 0 && index < kNumberOfHotObjects);
+      if (FLAG_trace_serializer) {
+        PrintF(" Encoding hot object %d:", index);
+        obj->ShortPrint();
+        PrintF("\n");
+      }
+      if (skip != 0) {
+        sink_->Put(kHotObjectWithSkip + index, "HotObjectWithSkip");
+        sink_->PutInt(skip, "HotObjectSkipDistance");
+      } else {
+        sink_->Put(kHotObject + index, "HotObject");
+      }
+      return true;
+    }
+  }
+  BackReference back_reference = back_reference_map_.Lookup(obj);
+  if (back_reference.is_valid()) {
+    // Encode the location of an already deserialized object in order to write
+    // its location into a later object.  We can encode the location as an
+    // offset fromthe start of the deserialized objects or as an offset
+    // backwards from thecurrent allocation pointer.
+    if (back_reference.is_source()) {
+      FlushSkip(skip);
+      if (FLAG_trace_serializer) PrintF(" Encoding source object\n");
+      DCHECK(how_to_code == kPlain && where_to_point == kStartOfObject);
+      sink_->Put(kAttachedReference + kPlain + kStartOfObject, "Source");
+      sink_->PutInt(kSourceObjectReference, "kSourceObjectReference");
+    } else if (back_reference.is_global_proxy()) {
+      FlushSkip(skip);
+      if (FLAG_trace_serializer) PrintF(" Encoding global proxy\n");
+      DCHECK(how_to_code == kPlain && where_to_point == kStartOfObject);
+      sink_->Put(kAttachedReference + kPlain + kStartOfObject, "Global Proxy");
+      sink_->PutInt(kGlobalProxyReference, "kGlobalProxyReference");
+    } else {
+      if (FLAG_trace_serializer) {
+        PrintF(" Encoding back reference to: ");
+        obj->ShortPrint();
+        PrintF("\n");
+      }
+
+      PutAlignmentPrefix(obj);
+      AllocationSpace space = back_reference.space();
+      if (skip == 0) {
+        sink_->Put(kBackref + how_to_code + where_to_point + space, "BackRef");
+      } else {
+        sink_->Put(kBackrefWithSkip + how_to_code + where_to_point + space,
+                   "BackRefWithSkip");
+        sink_->PutInt(skip, "BackRefSkipDistance");
+      }
+      PutBackReference(obj, back_reference);
+    }
+    return true;
+  }
+  return false;
+}
+
+void Serializer::PutRoot(int root_index, HeapObject* object,
+                         SerializerDeserializer::HowToCode how_to_code,
+                         SerializerDeserializer::WhereToPoint where_to_point,
+                         int skip) {
+  if (FLAG_trace_serializer) {
+    PrintF(" Encoding root %d:", root_index);
+    object->ShortPrint();
+    PrintF("\n");
+  }
+
+  if (how_to_code == kPlain && where_to_point == kStartOfObject &&
+      root_index < kNumberOfRootArrayConstants &&
+      !isolate()->heap()->InNewSpace(object)) {
+    if (skip == 0) {
+      sink_->Put(kRootArrayConstants + root_index, "RootConstant");
+    } else {
+      sink_->Put(kRootArrayConstantsWithSkip + root_index, "RootConstant");
+      sink_->PutInt(skip, "SkipInPutRoot");
+    }
+  } else {
+    FlushSkip(skip);
+    sink_->Put(kRootArray + how_to_code + where_to_point, "RootSerialization");
+    sink_->PutInt(root_index, "root_index");
+  }
+}
+
+void Serializer::PutBackReference(HeapObject* object, BackReference reference) {
+  DCHECK(BackReferenceIsAlreadyAllocated(reference));
+  sink_->PutInt(reference.reference(), "BackRefValue");
+  hot_objects_.Add(object);
+}
+
+int Serializer::PutAlignmentPrefix(HeapObject* object) {
+  AllocationAlignment alignment = object->RequiredAlignment();
+  if (alignment != kWordAligned) {
+    DCHECK(1 <= alignment && alignment <= 3);
+    byte prefix = (kAlignmentPrefix - 1) + alignment;
+    sink_->Put(prefix, "Alignment");
+    return Heap::GetMaximumFillToAlign(alignment);
+  }
+  return 0;
+}
+
+BackReference Serializer::AllocateLargeObject(int size) {
+  // Large objects are allocated one-by-one when deserializing. We do not
+  // have to keep track of multiple chunks.
+  large_objects_total_size_ += size;
+  return BackReference::LargeObjectReference(seen_large_objects_index_++);
+}
+
+BackReference Serializer::Allocate(AllocationSpace space, int size) {
+  DCHECK(space >= 0 && space < kNumberOfPreallocatedSpaces);
+  DCHECK(size > 0 && size <= static_cast<int>(max_chunk_size(space)));
+  uint32_t new_chunk_size = pending_chunk_[space] + size;
+  if (new_chunk_size > max_chunk_size(space)) {
+    // The new chunk size would not fit onto a single page. Complete the
+    // current chunk and start a new one.
+    sink_->Put(kNextChunk, "NextChunk");
+    sink_->Put(space, "NextChunkSpace");
+    completed_chunks_[space].Add(pending_chunk_[space]);
+    DCHECK_LE(completed_chunks_[space].length(), BackReference::kMaxChunkIndex);
+    pending_chunk_[space] = 0;
+    new_chunk_size = size;
+  }
+  uint32_t offset = pending_chunk_[space];
+  pending_chunk_[space] = new_chunk_size;
+  return BackReference::Reference(space, completed_chunks_[space].length(),
+                                  offset);
+}
+
+void Serializer::Pad() {
+  // The non-branching GetInt will read up to 3 bytes too far, so we need
+  // to pad the snapshot to make sure we don't read over the end.
+  for (unsigned i = 0; i < sizeof(int32_t) - 1; i++) {
+    sink_->Put(kNop, "Padding");
+  }
+  // Pad up to pointer size for checksum.
+  while (!IsAligned(sink_->Position(), kPointerAlignment)) {
+    sink_->Put(kNop, "Padding");
+  }
+}
+
+void Serializer::InitializeCodeAddressMap() {
+  isolate_->InitializeLoggingAndCounters();
+  code_address_map_ = new CodeAddressMap(isolate_);
+}
+
+Code* Serializer::CopyCode(Code* code) {
+  code_buffer_.Rewind(0);  // Clear buffer without deleting backing store.
+  int size = code->CodeSize();
+  code_buffer_.AddAll(Vector<byte>(code->address(), size));
+  return Code::cast(HeapObject::FromAddress(&code_buffer_.first()));
+}
+
+void Serializer::ObjectSerializer::SerializePrologue(AllocationSpace space,
+                                                     int size, Map* map) {
+  if (serializer_->code_address_map_) {
+    const char* code_name =
+        serializer_->code_address_map_->Lookup(object_->address());
+    LOG(serializer_->isolate_,
+        CodeNameEvent(object_->address(), sink_->Position(), code_name));
+    LOG(serializer_->isolate_,
+        SnapshotPositionEvent(object_->address(), sink_->Position()));
+  }
+
+  BackReference back_reference;
+  if (space == LO_SPACE) {
+    sink_->Put(kNewObject + reference_representation_ + space,
+               "NewLargeObject");
+    sink_->PutInt(size >> kObjectAlignmentBits, "ObjectSizeInWords");
+    if (object_->IsCode()) {
+      sink_->Put(EXECUTABLE, "executable large object");
+    } else {
+      sink_->Put(NOT_EXECUTABLE, "not executable large object");
+    }
+    back_reference = serializer_->AllocateLargeObject(size);
+  } else {
+    int fill = serializer_->PutAlignmentPrefix(object_);
+    back_reference = serializer_->Allocate(space, size + fill);
+    sink_->Put(kNewObject + reference_representation_ + space, "NewObject");
+    sink_->PutInt(size >> kObjectAlignmentBits, "ObjectSizeInWords");
+  }
+
+#ifdef OBJECT_PRINT
+  if (FLAG_serialization_statistics) {
+    serializer_->CountInstanceType(map, size);
+  }
+#endif  // OBJECT_PRINT
+
+  // Mark this object as already serialized.
+  serializer_->back_reference_map()->Add(object_, back_reference);
+
+  // Serialize the map (first word of the object).
+  serializer_->SerializeObject(map, kPlain, kStartOfObject, 0);
+}
+
+void Serializer::ObjectSerializer::SerializeExternalString() {
+  // Instead of serializing this as an external string, we serialize
+  // an imaginary sequential string with the same content.
+  Isolate* isolate = serializer_->isolate();
+  DCHECK(object_->IsExternalString());
+  DCHECK(object_->map() != isolate->heap()->native_source_string_map());
+  ExternalString* string = ExternalString::cast(object_);
+  int length = string->length();
+  Map* map;
+  int content_size;
+  int allocation_size;
+  const byte* resource;
+  // Find the map and size for the imaginary sequential string.
+  bool internalized = object_->IsInternalizedString();
+  if (object_->IsExternalOneByteString()) {
+    map = internalized ? isolate->heap()->one_byte_internalized_string_map()
+                       : isolate->heap()->one_byte_string_map();
+    allocation_size = SeqOneByteString::SizeFor(length);
+    content_size = length * kCharSize;
+    resource = reinterpret_cast<const byte*>(
+        ExternalOneByteString::cast(string)->resource()->data());
+  } else {
+    map = internalized ? isolate->heap()->internalized_string_map()
+                       : isolate->heap()->string_map();
+    allocation_size = SeqTwoByteString::SizeFor(length);
+    content_size = length * kShortSize;
+    resource = reinterpret_cast<const byte*>(
+        ExternalTwoByteString::cast(string)->resource()->data());
+  }
+
+  AllocationSpace space = (allocation_size > Page::kMaxRegularHeapObjectSize)
+                              ? LO_SPACE
+                              : OLD_SPACE;
+  SerializePrologue(space, allocation_size, map);
+
+  // Output the rest of the imaginary string.
+  int bytes_to_output = allocation_size - HeapObject::kHeaderSize;
+
+  // Output raw data header. Do not bother with common raw length cases here.
+  sink_->Put(kVariableRawData, "RawDataForString");
+  sink_->PutInt(bytes_to_output, "length");
+
+  // Serialize string header (except for map).
+  Address string_start = string->address();
+  for (int i = HeapObject::kHeaderSize; i < SeqString::kHeaderSize; i++) {
+    sink_->PutSection(string_start[i], "StringHeader");
+  }
+
+  // Serialize string content.
+  sink_->PutRaw(resource, content_size, "StringContent");
+
+  // Since the allocation size is rounded up to object alignment, there
+  // maybe left-over bytes that need to be padded.
+  int padding_size = allocation_size - SeqString::kHeaderSize - content_size;
+  DCHECK(0 <= padding_size && padding_size < kObjectAlignment);
+  for (int i = 0; i < padding_size; i++) sink_->PutSection(0, "StringPadding");
+
+  sink_->Put(kSkip, "SkipAfterString");
+  sink_->PutInt(bytes_to_output, "SkipDistance");
+}
+
+// Clear and later restore the next link in the weak cell or allocation site.
+// TODO(all): replace this with proper iteration of weak slots in serializer.
+class UnlinkWeakNextScope {
+ public:
+  explicit UnlinkWeakNextScope(HeapObject* object) : object_(nullptr) {
+    if (object->IsWeakCell()) {
+      object_ = object;
+      next_ = WeakCell::cast(object)->next();
+      WeakCell::cast(object)->clear_next(object->GetHeap()->the_hole_value());
+    } else if (object->IsAllocationSite()) {
+      object_ = object;
+      next_ = AllocationSite::cast(object)->weak_next();
+      AllocationSite::cast(object)->set_weak_next(
+          object->GetHeap()->undefined_value());
+    }
+  }
+
+  ~UnlinkWeakNextScope() {
+    if (object_ != nullptr) {
+      if (object_->IsWeakCell()) {
+        WeakCell::cast(object_)->set_next(next_, UPDATE_WEAK_WRITE_BARRIER);
+      } else {
+        AllocationSite::cast(object_)->set_weak_next(next_,
+                                                     UPDATE_WEAK_WRITE_BARRIER);
+      }
+    }
+  }
+
+ private:
+  HeapObject* object_;
+  Object* next_;
+  DisallowHeapAllocation no_gc_;
+};
+
+void Serializer::ObjectSerializer::Serialize() {
+  if (FLAG_trace_serializer) {
+    PrintF(" Encoding heap object: ");
+    object_->ShortPrint();
+    PrintF("\n");
+  }
+
+  // We cannot serialize typed array objects correctly.
+  DCHECK(!object_->IsJSTypedArray());
+
+  // We don't expect fillers.
+  DCHECK(!object_->IsFiller());
+
+  if (object_->IsScript()) {
+    // Clear cached line ends.
+    Object* undefined = serializer_->isolate()->heap()->undefined_value();
+    Script::cast(object_)->set_line_ends(undefined);
+  }
+
+  if (object_->IsExternalString()) {
+    Heap* heap = serializer_->isolate()->heap();
+    if (object_->map() != heap->native_source_string_map()) {
+      // Usually we cannot recreate resources for external strings. To work
+      // around this, external strings are serialized to look like ordinary
+      // sequential strings.
+      // The exception are native source code strings, since we can recreate
+      // their resources. In that case we fall through and leave it to
+      // VisitExternalOneByteString further down.
+      SerializeExternalString();
+      return;
+    }
+  }
+
+  int size = object_->Size();
+  Map* map = object_->map();
+  AllocationSpace space =
+      MemoryChunk::FromAddress(object_->address())->owner()->identity();
+  SerializePrologue(space, size, map);
+
+  // Serialize the rest of the object.
+  CHECK_EQ(0, bytes_processed_so_far_);
+  bytes_processed_so_far_ = kPointerSize;
+
+  RecursionScope recursion(serializer_);
+  // Objects that are immediately post processed during deserialization
+  // cannot be deferred, since post processing requires the object content.
+  if (recursion.ExceedsMaximum() && CanBeDeferred(object_)) {
+    serializer_->QueueDeferredObject(object_);
+    sink_->Put(kDeferred, "Deferring object content");
+    return;
+  }
+
+  UnlinkWeakNextScope unlink_weak_next(object_);
+
+  object_->IterateBody(map->instance_type(), size, this);
+  OutputRawData(object_->address() + size);
+}
+
+void Serializer::ObjectSerializer::SerializeDeferred() {
+  if (FLAG_trace_serializer) {
+    PrintF(" Encoding deferred heap object: ");
+    object_->ShortPrint();
+    PrintF("\n");
+  }
+
+  int size = object_->Size();
+  Map* map = object_->map();
+  BackReference reference = serializer_->back_reference_map()->Lookup(object_);
+
+  // Serialize the rest of the object.
+  CHECK_EQ(0, bytes_processed_so_far_);
+  bytes_processed_so_far_ = kPointerSize;
+
+  serializer_->PutAlignmentPrefix(object_);
+  sink_->Put(kNewObject + reference.space(), "deferred object");
+  serializer_->PutBackReference(object_, reference);
+  sink_->PutInt(size >> kPointerSizeLog2, "deferred object size");
+
+  UnlinkWeakNextScope unlink_weak_next(object_);
+
+  object_->IterateBody(map->instance_type(), size, this);
+  OutputRawData(object_->address() + size);
+}
+
+void Serializer::ObjectSerializer::VisitPointers(Object** start, Object** end) {
+  Object** current = start;
+  while (current < end) {
+    while (current < end && (*current)->IsSmi()) current++;
+    if (current < end) OutputRawData(reinterpret_cast<Address>(current));
+
+    while (current < end && !(*current)->IsSmi()) {
+      HeapObject* current_contents = HeapObject::cast(*current);
+      int root_index = serializer_->root_index_map()->Lookup(current_contents);
+      // Repeats are not subject to the write barrier so we can only use
+      // immortal immovable root members. They are never in new space.
+      if (current != start && root_index != RootIndexMap::kInvalidRootIndex &&
+          Heap::RootIsImmortalImmovable(root_index) &&
+          current_contents == current[-1]) {
+        DCHECK(!serializer_->isolate()->heap()->InNewSpace(current_contents));
+        int repeat_count = 1;
+        while (&current[repeat_count] < end - 1 &&
+               current[repeat_count] == current_contents) {
+          repeat_count++;
+        }
+        current += repeat_count;
+        bytes_processed_so_far_ += repeat_count * kPointerSize;
+        if (repeat_count > kNumberOfFixedRepeat) {
+          sink_->Put(kVariableRepeat, "VariableRepeat");
+          sink_->PutInt(repeat_count, "repeat count");
+        } else {
+          sink_->Put(kFixedRepeatStart + repeat_count, "FixedRepeat");
+        }
+      } else {
+        serializer_->SerializeObject(current_contents, kPlain, kStartOfObject,
+                                     0);
+        bytes_processed_so_far_ += kPointerSize;
+        current++;
+      }
+    }
+  }
+}
+
+void Serializer::ObjectSerializer::VisitEmbeddedPointer(RelocInfo* rinfo) {
+  int skip = OutputRawData(rinfo->target_address_address(),
+                           kCanReturnSkipInsteadOfSkipping);
+  HowToCode how_to_code = rinfo->IsCodedSpecially() ? kFromCode : kPlain;
+  Object* object = rinfo->target_object();
+  serializer_->SerializeObject(HeapObject::cast(object), how_to_code,
+                               kStartOfObject, skip);
+  bytes_processed_so_far_ += rinfo->target_address_size();
+}
+
+void Serializer::ObjectSerializer::VisitExternalReference(Address* p) {
+  int skip = OutputRawData(reinterpret_cast<Address>(p),
+                           kCanReturnSkipInsteadOfSkipping);
+  sink_->Put(kExternalReference + kPlain + kStartOfObject, "ExternalRef");
+  sink_->PutInt(skip, "SkipB4ExternalRef");
+  Address target = *p;
+  sink_->PutInt(serializer_->EncodeExternalReference(target), "reference id");
+  bytes_processed_so_far_ += kPointerSize;
+}
+
+void Serializer::ObjectSerializer::VisitExternalReference(RelocInfo* rinfo) {
+  int skip = OutputRawData(rinfo->target_address_address(),
+                           kCanReturnSkipInsteadOfSkipping);
+  HowToCode how_to_code = rinfo->IsCodedSpecially() ? kFromCode : kPlain;
+  sink_->Put(kExternalReference + how_to_code + kStartOfObject, "ExternalRef");
+  sink_->PutInt(skip, "SkipB4ExternalRef");
+  Address target = rinfo->target_external_reference();
+  sink_->PutInt(serializer_->EncodeExternalReference(target), "reference id");
+  bytes_processed_so_far_ += rinfo->target_address_size();
+}
+
+void Serializer::ObjectSerializer::VisitInternalReference(RelocInfo* rinfo) {
+  // We can only reference to internal references of code that has been output.
+  DCHECK(object_->IsCode() && code_has_been_output_);
+  // We do not use skip from last patched pc to find the pc to patch, since
+  // target_address_address may not return addresses in ascending order when
+  // used for internal references. External references may be stored at the
+  // end of the code in the constant pool, whereas internal references are
+  // inline. That would cause the skip to be negative. Instead, we store the
+  // offset from code entry.
+  Address entry = Code::cast(object_)->entry();
+  intptr_t pc_offset = rinfo->target_internal_reference_address() - entry;
+  intptr_t target_offset = rinfo->target_internal_reference() - entry;
+  DCHECK(0 <= pc_offset &&
+         pc_offset <= Code::cast(object_)->instruction_size());
+  DCHECK(0 <= target_offset &&
+         target_offset <= Code::cast(object_)->instruction_size());
+  sink_->Put(rinfo->rmode() == RelocInfo::INTERNAL_REFERENCE
+                 ? kInternalReference
+                 : kInternalReferenceEncoded,
+             "InternalRef");
+  sink_->PutInt(static_cast<uintptr_t>(pc_offset), "internal ref address");
+  sink_->PutInt(static_cast<uintptr_t>(target_offset), "internal ref value");
+}
+
+void Serializer::ObjectSerializer::VisitRuntimeEntry(RelocInfo* rinfo) {
+  int skip = OutputRawData(rinfo->target_address_address(),
+                           kCanReturnSkipInsteadOfSkipping);
+  HowToCode how_to_code = rinfo->IsCodedSpecially() ? kFromCode : kPlain;
+  sink_->Put(kExternalReference + how_to_code + kStartOfObject, "ExternalRef");
+  sink_->PutInt(skip, "SkipB4ExternalRef");
+  Address target = rinfo->target_address();
+  sink_->PutInt(serializer_->EncodeExternalReference(target), "reference id");
+  bytes_processed_so_far_ += rinfo->target_address_size();
+}
+
+void Serializer::ObjectSerializer::VisitCodeTarget(RelocInfo* rinfo) {
+  int skip = OutputRawData(rinfo->target_address_address(),
+                           kCanReturnSkipInsteadOfSkipping);
+  Code* object = Code::GetCodeFromTargetAddress(rinfo->target_address());
+  serializer_->SerializeObject(object, kFromCode, kInnerPointer, skip);
+  bytes_processed_so_far_ += rinfo->target_address_size();
+}
+
+void Serializer::ObjectSerializer::VisitCodeEntry(Address entry_address) {
+  int skip = OutputRawData(entry_address, kCanReturnSkipInsteadOfSkipping);
+  Code* object = Code::cast(Code::GetObjectFromEntryAddress(entry_address));
+  serializer_->SerializeObject(object, kPlain, kInnerPointer, skip);
+  bytes_processed_so_far_ += kPointerSize;
+}
+
+void Serializer::ObjectSerializer::VisitCell(RelocInfo* rinfo) {
+  int skip = OutputRawData(rinfo->pc(), kCanReturnSkipInsteadOfSkipping);
+  Cell* object = Cell::cast(rinfo->target_cell());
+  serializer_->SerializeObject(object, kPlain, kInnerPointer, skip);
+  bytes_processed_so_far_ += kPointerSize;
+}
+
+bool Serializer::ObjectSerializer::SerializeExternalNativeSourceString(
+    int builtin_count,
+    v8::String::ExternalOneByteStringResource** resource_pointer,
+    FixedArray* source_cache, int resource_index) {
+  for (int i = 0; i < builtin_count; i++) {
+    Object* source = source_cache->get(i);
+    if (!source->IsUndefined()) {
+      ExternalOneByteString* string = ExternalOneByteString::cast(source);
+      typedef v8::String::ExternalOneByteStringResource Resource;
+      const Resource* resource = string->resource();
+      if (resource == *resource_pointer) {
+        sink_->Put(resource_index, "NativesStringResource");
+        sink_->PutSection(i, "NativesStringResourceEnd");
+        bytes_processed_so_far_ += sizeof(resource);
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+void Serializer::ObjectSerializer::VisitExternalOneByteString(
+    v8::String::ExternalOneByteStringResource** resource_pointer) {
+  Address references_start = reinterpret_cast<Address>(resource_pointer);
+  OutputRawData(references_start);
+  if (SerializeExternalNativeSourceString(
+          Natives::GetBuiltinsCount(), resource_pointer,
+          Natives::GetSourceCache(serializer_->isolate()->heap()),
+          kNativesStringResource)) {
+    return;
+  }
+  if (SerializeExternalNativeSourceString(
+          ExtraNatives::GetBuiltinsCount(), resource_pointer,
+          ExtraNatives::GetSourceCache(serializer_->isolate()->heap()),
+          kExtraNativesStringResource)) {
+    return;
+  }
+  // One of the strings in the natives cache should match the resource.  We
+  // don't expect any other kinds of external strings here.
+  UNREACHABLE();
+}
+
+Address Serializer::ObjectSerializer::PrepareCode() {
+  // To make snapshots reproducible, we make a copy of the code object
+  // and wipe all pointers in the copy, which we then serialize.
+  Code* original = Code::cast(object_);
+  Code* code = serializer_->CopyCode(original);
+  // Code age headers are not serializable.
+  code->MakeYoung(serializer_->isolate());
+  int mode_mask = RelocInfo::kCodeTargetMask |
+                  RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT) |
+                  RelocInfo::ModeMask(RelocInfo::EXTERNAL_REFERENCE) |
+                  RelocInfo::ModeMask(RelocInfo::RUNTIME_ENTRY) |
+                  RelocInfo::ModeMask(RelocInfo::INTERNAL_REFERENCE) |
+                  RelocInfo::ModeMask(RelocInfo::INTERNAL_REFERENCE_ENCODED);
+  for (RelocIterator it(code, mode_mask); !it.done(); it.next()) {
+    RelocInfo* rinfo = it.rinfo();
+    rinfo->WipeOut();
+  }
+  // We need to wipe out the header fields *after* wiping out the
+  // relocations, because some of these fields are needed for the latter.
+  code->WipeOutHeader();
+  return code->address();
+}
+
+int Serializer::ObjectSerializer::OutputRawData(
+    Address up_to, Serializer::ObjectSerializer::ReturnSkip return_skip) {
+  Address object_start = object_->address();
+  int base = bytes_processed_so_far_;
+  int up_to_offset = static_cast<int>(up_to - object_start);
+  int to_skip = up_to_offset - bytes_processed_so_far_;
+  int bytes_to_output = to_skip;
+  bytes_processed_so_far_ += to_skip;
+  // This assert will fail if the reloc info gives us the target_address_address
+  // locations in a non-ascending order.  Luckily that doesn't happen.
+  DCHECK(to_skip >= 0);
+  bool outputting_code = false;
+  bool is_code_object = object_->IsCode();
+  if (to_skip != 0 && is_code_object && !code_has_been_output_) {
+    // Output the code all at once and fix later.
+    bytes_to_output = object_->Size() + to_skip - bytes_processed_so_far_;
+    outputting_code = true;
+    code_has_been_output_ = true;
+  }
+  if (bytes_to_output != 0 && (!is_code_object || outputting_code)) {
+    if (!outputting_code && bytes_to_output == to_skip &&
+        IsAligned(bytes_to_output, kPointerAlignment) &&
+        bytes_to_output <= kNumberOfFixedRawData * kPointerSize) {
+      int size_in_words = bytes_to_output >> kPointerSizeLog2;
+      sink_->PutSection(kFixedRawDataStart + size_in_words, "FixedRawData");
+      to_skip = 0;  // This instruction includes skip.
+    } else {
+      // We always end up here if we are outputting the code of a code object.
+      sink_->Put(kVariableRawData, "VariableRawData");
+      sink_->PutInt(bytes_to_output, "length");
+    }
+
+    if (is_code_object) object_start = PrepareCode();
+
+    const char* description = is_code_object ? "Code" : "Byte";
+    sink_->PutRaw(object_start + base, bytes_to_output, description);
+  }
+  if (to_skip != 0 && return_skip == kIgnoringReturn) {
+    sink_->Put(kSkip, "Skip");
+    sink_->PutInt(to_skip, "SkipDistance");
+    to_skip = 0;
+  }
+  return to_skip;
+}
+
+}  // namespace internal
+}  // namespace v8