src/snapshot/snapshot-data.cc

// Copyright 2020 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/snapshot-data.h"

#include "src/common/assert-scope.h"
#include "src/snapshot/serializer.h"

#ifdef V8_SNAPSHOT_COMPRESSION
#include "src/snapshot/snapshot-compression.h"
#endif

namespace v8 {
namespace internal {

void SerializedData::AllocateData(uint32_t size) {
  DCHECK(!owns_data_);
  data_ = NewArray<byte>(size);
  size_ = size;
  owns_data_ = true;
}

// static
constexpr uint32_t SerializedData::kMagicNumber;

SnapshotData::SnapshotData(const Serializer* serializer) {
  DisallowHeapAllocation no_gc;
  std::vector<Reservation> reservations = serializer->EncodeReservations();
  const std::vector<byte>* payload = serializer->Payload();

  // Calculate sizes.
  uint32_t reservation_size =
      static_cast<uint32_t>(reservations.size()) * kUInt32Size;
  uint32_t payload_offset = kHeaderSize + reservation_size;
  uint32_t padded_payload_offset = POINTER_SIZE_ALIGN(payload_offset);
  uint32_t size =
      padded_payload_offset + static_cast<uint32_t>(payload->size());

  // Allocate backing store and create result data.
  AllocateData(size);

  // Zero out pre-payload data. Part of that is only used for padding.
  memset(data_, 0, padded_payload_offset);

  // Set header values.
  SetMagicNumber();
  SetHeaderValue(kNumReservationsOffset, static_cast<int>(reservations.size()));
  SetHeaderValue(kPayloadLengthOffset, static_cast<int>(payload->size()));

  // Copy reservation chunk sizes.
  CopyBytes(data_ + kHeaderSize, reinterpret_cast<byte*>(reservations.data()),
            reservation_size);

  // Copy serialized data.
  CopyBytes(data_ + padded_payload_offset, payload->data(),
            static_cast<size_t>(payload->size()));
}

std::vector<SerializedData::Reservation> SnapshotData::Reservations() const {
  uint32_t size = GetHeaderValue(kNumReservationsOffset);
  std::vector<SerializedData::Reservation> reservations(size);
  memcpy(reservations.data(), data_ + kHeaderSize,
         size * sizeof(SerializedData::Reservation));
  return reservations;
}

Vector<const byte> SnapshotData::Payload() const {
  uint32_t reservations_size =
      GetHeaderValue(kNumReservationsOffset) * kUInt32Size;
  uint32_t padded_payload_offset =
      POINTER_SIZE_ALIGN(kHeaderSize + reservations_size);
  const byte* payload = data_ + padded_payload_offset;
  uint32_t length = GetHeaderValue(kPayloadLengthOffset);
  DCHECK_EQ(data_ + size_, payload + length);
  return Vector<const byte>(payload, length);
}

}  // namespace internal
}  // namespace v8