src/snapshot/serializer-common.h

// 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.

#ifndef V8_SNAPSHOT_SERIALIZER_COMMON_H_
#define V8_SNAPSHOT_SERIALIZER_COMMON_H_

#include "src/address-map.h"
#include "src/base/bits.h"
#include "src/external-reference-table.h"
#include "src/globals.h"
#include "src/snapshot/references.h"
#include "src/v8memory.h"
#include "src/visitors.h"

namespace v8 {
namespace internal {

class CallHandlerInfo;
class Isolate;

class ExternalReferenceEncoder {
 public:
  class Value {
   public:
    explicit Value(uint32_t raw) : value_(raw) {}
    Value() : value_(0) {}
    static uint32_t Encode(uint32_t index, bool is_from_api) {
      return Index::encode(index) | IsFromAPI::encode(is_from_api);
    }

    bool is_from_api() const { return IsFromAPI::decode(value_); }
    uint32_t index() const { return Index::decode(value_); }

   private:
    class Index : public BitField<uint32_t, 0, 31> {};
    class IsFromAPI : public BitField<bool, 31, 1> {};
    uint32_t value_;
  };

  explicit ExternalReferenceEncoder(Isolate* isolate);
  ~ExternalReferenceEncoder();

  Value Encode(Address key);
  Maybe<Value> TryEncode(Address key);

  const char* NameOfAddress(Isolate* isolate, Address address) const;

 private:
  AddressToIndexHashMap* map_;

#ifdef DEBUG
  std::vector<int> count_;
  const intptr_t* api_references_;
#endif  // DEBUG

  DISALLOW_COPY_AND_ASSIGN(ExternalReferenceEncoder);
};

class HotObjectsList {
 public:
  HotObjectsList() : index_(0) {
    for (int i = 0; i < kSize; i++) circular_queue_[i] = nullptr;
  }

  void Add(HeapObject* object) {
    DCHECK(!AllowHeapAllocation::IsAllowed());
    circular_queue_[index_] = object;
    index_ = (index_ + 1) & kSizeMask;
  }

  HeapObject* Get(int index) {
    DCHECK(!AllowHeapAllocation::IsAllowed());
    DCHECK_NOT_NULL(circular_queue_[index]);
    return circular_queue_[index];
  }

  static const int kNotFound = -1;

  int Find(HeapObject* object) {
    DCHECK(!AllowHeapAllocation::IsAllowed());
    for (int i = 0; i < kSize; i++) {
      if (circular_queue_[i] == object) return i;
    }
    return kNotFound;
  }

  static const int kSize = 8;

 private:
  static_assert(base::bits::IsPowerOfTwo(kSize), "kSize must be power of two");
  static const int kSizeMask = kSize - 1;
  HeapObject* circular_queue_[kSize];
  int index_;

  DISALLOW_COPY_AND_ASSIGN(HotObjectsList);
};

// The Serializer/Deserializer class is a common superclass for Serializer and
// Deserializer which is used to store common constants and methods used by
// both.
class SerializerDeserializer : public RootVisitor {
 public:
  static void Iterate(Isolate* isolate, RootVisitor* visitor);

  // No reservation for large object space necessary.
  // We also handle map space differenly.
  STATIC_ASSERT(MAP_SPACE == CODE_SPACE + 1);

  // We do not support young generation large objects.
  STATIC_ASSERT(LAST_SPACE == NEW_LO_SPACE);
  STATIC_ASSERT(LAST_SPACE - 1 == LO_SPACE);
  static const int kNumberOfPreallocatedSpaces = CODE_SPACE + 1;
  static const int kNumberOfSpaces = LO_SPACE + 1;

 protected:
  static bool CanBeDeferred(HeapObject* o);

  void RestoreExternalReferenceRedirectors(
      const std::vector<AccessorInfo*>& accessor_infos);
  void RestoreExternalReferenceRedirectors(
      const std::vector<CallHandlerInfo*>& call_handler_infos);

#define UNUSED_SERIALIZER_BYTE_CODES(V) \
  V(0x18)                               \
  V(0x3d)                               \
  V(0x3e)                               \
  V(0x3f)                               \
  V(0x58)                               \
  V(0x59)                               \
  V(0x5a)                               \
  V(0x5b)                               \
  V(0x5c)                               \
  V(0x5d)                               \
  V(0x5e)                               \
  V(0x5f)                               \
  V(0x67)                               \
  V(0x76)                               \
  V(0x78)                               \
  V(0x79)                               \
  V(0x7a)                               \
  V(0x7b)                               \
  V(0x7c)                               \
  V(0x7d)

  // ---------- byte code range 0x00..0x7f ----------
  // Byte codes in this range represent Where, HowToCode and WhereToPoint.
  // Where the pointed-to object can be found:
  // The static assert below will trigger when the number of preallocated spaces
  // changed. If that happens, update the bytecode ranges in the comments below.
  STATIC_ASSERT(6 == kNumberOfSpaces);
  enum Where {
    // 0x00..0x05  Allocate new object, in specified space.
    kNewObject = 0x00,
    // 0x08..0x0d  Reference to previous object from space.
    kBackref = 0x08,
    // 0x10..0x15  Reference to previous object from space after skip.
    kBackrefWithSkip = 0x10,

    // 0x06        Object in the partial snapshot cache.
    kPartialSnapshotCache = 0x06,
    // 0x07        External reference referenced by id.
    kExternalReference = 0x07,

    // 0x0e        Builtin code referenced by index.
    kBuiltin = 0x0e,
    // 0x16       Root array item.
    kRootArray = 0x16,
    // 0x17        Object provided in the attached list.
    kAttachedReference = 0x17,

    // 0x0f        Misc, see below (incl. 0x2f, 0x4f, 0x6f).
    // 0x18..0x1f  Misc, see below (incl. 0x38..0x3f, 0x58..0x5f, 0x78..0x7f).
  };

  static const int kWhereMask = 0x1f;
  static const int kSpaceMask = 7;
  STATIC_ASSERT(kNumberOfSpaces <= kSpaceMask + 1);

  // How to code the pointer to the object.
  enum HowToCode {
    // Straight pointer.
    kPlain = 0,
    // A pointer inlined in code. What this means depends on the architecture.
    kFromCode = 0x20
  };

  static const int kHowToCodeMask = 0x20;

  // Where to point within the object.
  enum WhereToPoint {
    // Points to start of object
    kStartOfObject = 0,
    // Points to instruction in code object or payload of cell.
    kInnerPointer = 0x40
  };

  static const int kWhereToPointMask = 0x40;

  // ---------- Misc ----------
  // Skip.
  static const int kSkip = 0x0f;
  // Do nothing, used for padding.
  static const int kNop = 0x2f;
  // Move to next reserved chunk.
  static const int kNextChunk = 0x4f;
  // Deferring object content.
  static const int kDeferred = 0x6f;
  // Alignment prefixes 0x19..0x1b
  static const int kAlignmentPrefix = 0x19;
  // A tag emitted at strategic points in the snapshot to delineate sections.
  // If the deserializer does not find these at the expected moments then it
  // is an indication that the snapshot and the VM do not fit together.
  // Examine the build process for architecture, version or configuration
  // mismatches.
  static const int kSynchronize = 0x1c;
  // Repeats of variable length.
  static const int kVariableRepeat = 0x1d;
  // Raw data of variable length.

  // Used for embedder-allocated backing stores for TypedArrays.
  static const int kOffHeapBackingStore = 0x1e;

  // Used for embedder-provided serialization data for embedder fields.
  static const int kEmbedderFieldsData = 0x1f;

  // Used to encode external referenced provided through the API.
  static const int kApiReference = 0x38;

  static const int kVariableRawCode = 0x39;
  static const int kVariableRawData = 0x3a;

  static const int kInternalReference = 0x3b;
  static const int kInternalReferenceEncoded = 0x3c;

  // In-place weak references
  static const int kWeakPrefix = 0x7e;

  // Encodes an off-heap instruction stream target.
  static const int kOffHeapTarget = 0x7f;

  // ---------- byte code range 0x80..0xff ----------
  // First 32 root array items.
  static const int kNumberOfRootArrayConstants = 0x20;
  // 0x80..0x9f
  static const int kRootArrayConstants = 0x80;
  // 0xa0..0xbf
  static const int kRootArrayConstantsWithSkip = 0xa0;
  static const int kRootArrayConstantsMask = 0x1f;

  // 32 common raw data lengths.
  static const int kNumberOfFixedRawData = 0x20;
  // 0xc0..0xdf
  static const int kFixedRawData = 0xc0;
  static const int kOnePointerRawData = kFixedRawData;
  static const int kFixedRawDataStart = kFixedRawData - 1;

  // 16 repeats lengths.
  static const int kNumberOfFixedRepeat = 0x10;
  // 0xe0..0xef
  static const int kFixedRepeat = 0xe0;
  static const int kFixedRepeatStart = kFixedRepeat - 1;

  // 8 hot (recently seen or back-referenced) objects with optional skip.
  static const int kNumberOfHotObjects = 8;
  STATIC_ASSERT(kNumberOfHotObjects == HotObjectsList::kSize);
  // 0xf0..0xf7
  static const int kHotObject = 0xf0;
  // 0xf8..0xff
  static const int kHotObjectWithSkip = 0xf8;
  static const int kHotObjectMask = 0x07;

  // ---------- special values ----------
  static const int kAnyOldSpace = -1;

  // Sentinel after a new object to indicate that double alignment is needed.
  static const int kDoubleAlignmentSentinel = 0;

  // ---------- member variable ----------
  HotObjectsList hot_objects_;
};

class SerializedData {
 public:
  class Reservation {
   public:
    Reservation() : reservation_(0) {}
    explicit Reservation(uint32_t size)
        : reservation_(ChunkSizeBits::encode(size)) {}

    uint32_t chunk_size() const { return ChunkSizeBits::decode(reservation_); }
    bool is_last() const { return IsLastChunkBits::decode(reservation_); }

    void mark_as_last() { reservation_ |= IsLastChunkBits::encode(true); }

   private:
    uint32_t reservation_;
  };

  SerializedData(byte* data, int size)
      : data_(data), size_(size), owns_data_(false) {}
  SerializedData() : data_(nullptr), size_(0), owns_data_(false) {}
  SerializedData(SerializedData&& other) V8_NOEXCEPT
      : data_(other.data_),
        size_(other.size_),
        owns_data_(other.owns_data_) {
    // Ensure |other| will not attempt to destroy our data in destructor.
    other.owns_data_ = false;
  }

  virtual ~SerializedData() {
    if (owns_data_) DeleteArray<byte>(data_);
  }

  uint32_t GetMagicNumber() const { return GetHeaderValue(kMagicNumberOffset); }

  class ChunkSizeBits : public BitField<uint32_t, 0, 31> {};
  class IsLastChunkBits : public BitField<bool, 31, 1> {};

  static uint32_t ComputeMagicNumber(ExternalReferenceTable* table) {
    uint32_t external_refs = table->size();
    return 0xC0DE0000 ^ external_refs;
  }

  static const uint32_t kMagicNumberOffset = 0;

 protected:
  void SetHeaderValue(uint32_t offset, uint32_t value) {
    WriteLittleEndianValue(reinterpret_cast<Address>(data_) + offset, value);
  }

  uint32_t GetHeaderValue(uint32_t offset) const {
    return ReadLittleEndianValue<uint32_t>(reinterpret_cast<Address>(data_) +
                                           offset);
  }

  void AllocateData(uint32_t size);

  static uint32_t ComputeMagicNumber(Isolate* isolate);

  void SetMagicNumber(Isolate* isolate) {
    SetHeaderValue(kMagicNumberOffset, ComputeMagicNumber(isolate));
  }

  byte* data_;
  uint32_t size_;
  bool owns_data_;

 private:
  DISALLOW_COPY_AND_ASSIGN(SerializedData);
};

}  // namespace internal
}  // namespace v8

#endif  // V8_SNAPSHOT_SERIALIZER_COMMON_H_