snapshot.h

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// 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.
 
#ifndef V8_SNAPSHOT_SNAPSHOT_H_
#define V8_SNAPSHOT_SNAPSHOT_H_
 
#include <vector>
 
#include "include/v8-array-buffer.h"  // For ArrayBuffer::Allocator.
#include "include/v8-snapshot.h"  // For StartupData.
#include "src/common/assert-scope.h"
#include "src/common/globals.h"
#include "src/snapshot/serializer-deserializer.h"
 
namespace v8 {
namespace internal {
 
class Context;
class Isolate;
class JSGlobalProxy;
class SafepointScope;
class SnapshotData;
 
class Snapshot : public AllStatic {
 public:
  // ---------------- Serialization -------------------------------------------
 
  enum SerializerFlag {
    // If set, serializes unknown external references as verbatim data. This
    // usually leads to invalid state if the snapshot is deserialized in a
    // different isolate or a different process.
    // If unset, all external references must be known to the encoder.
    kAllowUnknownExternalReferencesForTesting = 1 << 0,
    // If set, the serializer enters a more permissive mode which allows
    // serialization of a currently active, running isolate. This has multiple
    // effects; for example, open handles are allowed, microtasks may exist,
    // etc. Note that in this mode, the serializer is allowed to skip
    // visitation of certain problematic areas even if they are non-empty. The
    // resulting snapshot is not guaranteed to result in a runnable context
    // after deserialization.
    // If unset, we assert that these previously mentioned areas are empty.
    kAllowActiveIsolateForTesting = 1 << 1,
    // If set, the ReadOnlySerializer and the SharedHeapSerializer reconstructs
    // their respective object caches from the existing ReadOnlyHeap's read-only
    // object cache or the existing shared heap's object cache so the same
    // mapping is used.  This mode is used for testing deserialization of a
    // snapshot from a live isolate that's using a shared ReadOnlyHeap or is
    // attached to a shared isolate. Otherwise during deserialization the
    // indices will mismatch, causing deserialization crashes when e.g. types
    // mismatch.  If unset, the read-only object cache is populated as read-only
    // objects are serialized, and the shared heap object cache is populated as
    // shared heap objects are serialized.
    kReconstructReadOnlyAndSharedObjectCachesForTesting = 1 << 2,
  };
  using SerializerFlags = base::Flags<SerializerFlag>;
  V8_EXPORT_PRIVATE static constexpr SerializerFlags kDefaultSerializerFlags =
      {};
 
  // In preparation for serialization, clear data from the given isolate's heap
  // that 1. can be reconstructed and 2. is not suitable for serialization. The
  // `clear_recompilable_data` flag controls whether compiled objects are
  // cleared from shared function infos and regexp objects.
  V8_EXPORT_PRIVATE static void ClearReconstructableDataForSerialization(
      Isolate* isolate, bool clear_recompilable_data);
 
  // Serializes the given isolate and contexts. Each context may have an
  // associated callback to serialize internal fields. The default context must
  // be passed at index 0.
  static v8::StartupData Create(
      Isolate* isolate, std::vector<Tagged<Context>>* contexts,
      const std::vector<SerializeEmbedderFieldsCallback>&
          embedder_fields_serializers,
      const SafepointScope& safepoint_scope,
      const DisallowGarbageCollection& no_gc,
      SerializerFlags flags = kDefaultSerializerFlags);
 
  // ---------------- Deserialization -----------------------------------------
 
  // Initialize the Isolate from the internal snapshot. Returns false if no
  // snapshot could be found.
  static bool Initialize(Isolate* isolate);
 
  // Create a new context using the internal context snapshot.
  static MaybeDirectHandle<Context> NewContextFromSnapshot(
      Isolate* isolate, DirectHandle<JSGlobalProxy> global_proxy,
      size_t context_index,
      DeserializeEmbedderFieldsCallback embedder_fields_deserializer);
 
  // ---------------- Testing -------------------------------------------------
 
  // This function is used to stress the snapshot component. It serializes the
  // current isolate and context into a snapshot, deserializes the snapshot into
  // a new isolate and context, and finally runs VerifyHeap on the fresh
  // isolate.
  V8_EXPORT_PRIVATE static void SerializeDeserializeAndVerifyForTesting(
      Isolate* isolate, DirectHandle<Context> default_context);
 
  // ---------------- Helper methods ------------------------------------------
 
  static bool HasContextSnapshot(Isolate* isolate, size_t index);
  static bool EmbedsScript(Isolate* isolate);
  V8_EXPORT_PRIVATE static uint32_t GetExpectedChecksum(
      const v8::StartupData* data);
  V8_EXPORT_PRIVATE static uint32_t CalculateChecksum(
      const v8::StartupData* data);
  V8_EXPORT_PRIVATE static bool VerifyChecksum(const v8::StartupData* data);
  static bool ExtractRehashability(const v8::StartupData* data);
  V8_EXPORT_PRIVATE static uint32_t ExtractReadOnlySnapshotChecksum(
      const v8::StartupData* data);
  static bool VersionIsValid(const v8::StartupData* data);
 
  // To be implemented by the snapshot source.
  static const v8::StartupData* DefaultSnapshotBlob();
  static bool ShouldVerifyChecksum(const v8::StartupData* data);
 
#ifdef DEBUG
  static bool SnapshotIsValid(const v8::StartupData* snapshot_blob);
#endif  // DEBUG
};
 
// Convenience wrapper around snapshot data blob creation used e.g. by tests.
V8_EXPORT_PRIVATE v8::StartupData CreateSnapshotDataBlobInternal(
    v8::SnapshotCreator::FunctionCodeHandling function_code_handling,
    const char* embedded_source = nullptr,
    Snapshot::SerializerFlags serializer_flags =
        Snapshot::kDefaultSerializerFlags);
// Convenience wrapper around snapshot data blob creation used e.g. by
// mksnapshot.
V8_EXPORT_PRIVATE v8::StartupData CreateSnapshotDataBlobInternal(
    v8::SnapshotCreator::FunctionCodeHandling function_code_handling,
    const char* embedded_source, v8::SnapshotCreator& snapshot_creator,
    Snapshot::SerializerFlags serializer_flags =
        Snapshot::kDefaultSerializerFlags);
// .. and for inspector-test.cc which needs an extern declaration due to
// restrictive include rules:
V8_EXPORT_PRIVATE v8::StartupData
CreateSnapshotDataBlobInternalForInspectorTest(
    v8::SnapshotCreator::FunctionCodeHandling function_code_handling,
    const char* embedded_source);
 
// Convenience wrapper around snapshot data blob warmup used e.g. by tests and
// mksnapshot.
V8_EXPORT_PRIVATE v8::StartupData WarmUpSnapshotDataBlobInternal(
    v8::StartupData cold_snapshot_blob, const char* warmup_source);
 
#ifdef V8_USE_EXTERNAL_STARTUP_DATA
void SetSnapshotFromFile(StartupData* snapshot_blob);
#endif
 
// The implementation of the API-exposed class SnapshotCreator.
class SnapshotCreatorImpl final {
 public:
  // This ctor is used for internal usages:
  // 1. %ProfileCreateSnapshotDataBlob(): Needs to hook into an existing
  //    Isolate.
  //
  // TODO(v8:14490): Refactor 1. to go through the public API and simplify this
  // part of the internal snapshot creator.
  SnapshotCreatorImpl(Isolate* isolate, const intptr_t* api_external_references,
                      const StartupData* existing_blob, bool owns_isolate);
  explicit SnapshotCreatorImpl(const v8::Isolate::CreateParams& params);
 
  SnapshotCreatorImpl(Isolate* isolate,
                      const v8::Isolate::CreateParams& params);
 
  ~SnapshotCreatorImpl();
 
  Isolate* isolate() const { return isolate_; }
 
  void SetDefaultContext(DirectHandle<NativeContext> context,
                         SerializeEmbedderFieldsCallback callback);
  size_t AddContext(DirectHandle<NativeContext> context,
                    SerializeEmbedderFieldsCallback callback);
 
  size_t AddData(DirectHandle<NativeContext> context, Address object);
  size_t AddData(Address object);
 
  StartupData CreateBlob(
      SnapshotCreator::FunctionCodeHandling function_code_handling,
      Snapshot::SerializerFlags serializer_flags =
          Snapshot::kDefaultSerializerFlags);
 
  static SnapshotCreatorImpl* FromSnapshotCreator(
      v8::SnapshotCreator* snapshot_creator);
 
  static constexpr size_t kDefaultContextIndex = 0;
  static constexpr size_t kFirstAddtlContextIndex = kDefaultContextIndex + 1;
 
 private:
  struct SerializableContext {
    SerializableContext() : handle_location(nullptr), callback(nullptr) {}
    SerializableContext(Address* handle_location,
                        SerializeEmbedderFieldsCallback callback)
        : handle_location(handle_location), callback(callback) {}
    Address* handle_location = nullptr;  // A GlobalHandle.
    SerializeEmbedderFieldsCallback callback;
  };
 
  void InitInternal(const StartupData*);
 
  DirectHandle<NativeContext> context_at(size_t i) const;
  bool created() const { return contexts_.size() == 0; }
 
  const bool owns_isolate_;
  Isolate* const isolate_;
  std::unique_ptr<v8::ArrayBuffer::Allocator> array_buffer_allocator_;
  std::vector<SerializableContext> contexts_;
};
 
}  // namespace internal
}  // namespace v8
 
#endif  // V8_SNAPSHOT_SNAPSHOT_H_