// 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/snapshot/snapshot.h" #include "src/base/platform/platform.h" #include "src/logging/counters.h" #include "src/snapshot/context-deserializer.h" #include "src/snapshot/read-only-deserializer.h" #include "src/snapshot/snapshot-utils.h" #include "src/snapshot/startup-deserializer.h" #include "src/utils/memcopy.h" #include "src/utils/version.h" #ifdef V8_SNAPSHOT_COMPRESSION #include "src/snapshot/snapshot-compression.h" #endif namespace v8 { namespace internal { namespace { class SnapshotImpl : public AllStatic { public: static uint32_t ExtractNumContexts(const v8::StartupData* data); static uint32_t ExtractContextOffset(const v8::StartupData* data, uint32_t index); static Vector<const byte> ExtractStartupData(const v8::StartupData* data); static Vector<const byte> ExtractReadOnlyData(const v8::StartupData* data); static Vector<const byte> ExtractContextData(const v8::StartupData* data, uint32_t index); static uint32_t GetHeaderValue(const v8::StartupData* data, uint32_t offset) { return base::ReadLittleEndianValue<uint32_t>( reinterpret_cast<Address>(data->data) + offset); } static void SetHeaderValue(char* data, uint32_t offset, uint32_t value) { base::WriteLittleEndianValue(reinterpret_cast<Address>(data) + offset, value); } static void CheckVersion(const v8::StartupData* data); // Snapshot blob layout: // [0] number of contexts N // [1] rehashability // [2] checksum // [3] (128 bytes) version string // [4] offset to readonly // [5] offset to context 0 // [6] offset to context 1 // ... // ... offset to context N - 1 // ... startup snapshot data // ... read-only snapshot data // ... context 0 snapshot data // ... context 1 snapshot data static const uint32_t kNumberOfContextsOffset = 0; // TODO(yangguo): generalize rehashing, and remove this flag. static const uint32_t kRehashabilityOffset = kNumberOfContextsOffset + kUInt32Size; static const uint32_t kChecksumOffset = kRehashabilityOffset + kUInt32Size; static const uint32_t kVersionStringOffset = kChecksumOffset + kUInt32Size; static const uint32_t kVersionStringLength = 64; static const uint32_t kReadOnlyOffsetOffset = kVersionStringOffset + kVersionStringLength; static const uint32_t kFirstContextOffsetOffset = kReadOnlyOffsetOffset + kUInt32Size; static Vector<const byte> ChecksummedContent(const v8::StartupData* data) { STATIC_ASSERT(kVersionStringOffset == kChecksumOffset + kUInt32Size); const uint32_t kChecksumStart = kVersionStringOffset; return Vector<const byte>( reinterpret_cast<const byte*>(data->data + kChecksumStart), data->raw_size - kChecksumStart); } static uint32_t StartupSnapshotOffset(int num_contexts) { return POINTER_SIZE_ALIGN(kFirstContextOffsetOffset + num_contexts * kInt32Size); } static uint32_t ContextSnapshotOffsetOffset(int index) { return kFirstContextOffsetOffset + index * kInt32Size; } }; } // namespace SnapshotData MaybeDecompress(const Vector<const byte>& snapshot_data) { #ifdef V8_SNAPSHOT_COMPRESSION return SnapshotCompression::Decompress(snapshot_data); #else return SnapshotData(snapshot_data); #endif } #ifdef DEBUG bool Snapshot::SnapshotIsValid(const v8::StartupData* snapshot_blob) { return SnapshotImpl::ExtractNumContexts(snapshot_blob) > 0; } #endif // DEBUG bool Snapshot::HasContextSnapshot(Isolate* isolate, size_t index) { // Do not use snapshots if the isolate is used to create snapshots. const v8::StartupData* blob = isolate->snapshot_blob(); if (blob == nullptr) return false; if (blob->data == nullptr) return false; size_t num_contexts = static_cast<size_t>(SnapshotImpl::ExtractNumContexts(blob)); return index < num_contexts; } bool Snapshot::Initialize(Isolate* isolate) { if (!isolate->snapshot_available()) return false; RuntimeCallTimerScope rcs_timer(isolate, RuntimeCallCounterId::kDeserializeIsolate); base::ElapsedTimer timer; if (FLAG_profile_deserialization) timer.Start(); const v8::StartupData* blob = isolate->snapshot_blob(); SnapshotImpl::CheckVersion(blob); CHECK(VerifyChecksum(blob)); Vector<const byte> startup_data = SnapshotImpl::ExtractStartupData(blob); Vector<const byte> read_only_data = SnapshotImpl::ExtractReadOnlyData(blob); SnapshotData startup_snapshot_data(MaybeDecompress(startup_data)); SnapshotData read_only_snapshot_data(MaybeDecompress(read_only_data)); StartupDeserializer startup_deserializer(&startup_snapshot_data); ReadOnlyDeserializer read_only_deserializer(&read_only_snapshot_data); startup_deserializer.SetRehashability(ExtractRehashability(blob)); read_only_deserializer.SetRehashability(ExtractRehashability(blob)); bool success = isolate->InitWithSnapshot(&read_only_deserializer, &startup_deserializer); if (FLAG_profile_deserialization) { double ms = timer.Elapsed().InMillisecondsF(); int bytes = startup_data.length(); PrintF("[Deserializing isolate (%d bytes) took %0.3f ms]\n", bytes, ms); } return success; } MaybeHandle<Context> Snapshot::NewContextFromSnapshot( Isolate* isolate, Handle<JSGlobalProxy> global_proxy, size_t context_index, v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer) { if (!isolate->snapshot_available()) return Handle<Context>(); RuntimeCallTimerScope rcs_timer(isolate, RuntimeCallCounterId::kDeserializeContext); base::ElapsedTimer timer; if (FLAG_profile_deserialization) timer.Start(); const v8::StartupData* blob = isolate->snapshot_blob(); bool can_rehash = ExtractRehashability(blob); Vector<const byte> context_data = SnapshotImpl::ExtractContextData( blob, static_cast<uint32_t>(context_index)); SnapshotData snapshot_data(MaybeDecompress(context_data)); MaybeHandle<Context> maybe_result = ContextDeserializer::DeserializeContext( isolate, &snapshot_data, can_rehash, global_proxy, embedder_fields_deserializer); Handle<Context> result; if (!maybe_result.ToHandle(&result)) return MaybeHandle<Context>(); if (FLAG_profile_deserialization) { double ms = timer.Elapsed().InMillisecondsF(); int bytes = context_data.length(); PrintF("[Deserializing context #%zu (%d bytes) took %0.3f ms]\n", context_index, bytes, ms); } return result; } void ProfileDeserialization( const SnapshotData* read_only_snapshot, const SnapshotData* startup_snapshot, const std::vector<SnapshotData*>& context_snapshots) { if (FLAG_profile_deserialization) { int startup_total = 0; PrintF("Deserialization will reserve:\n"); for (const auto& reservation : read_only_snapshot->Reservations()) { startup_total += reservation.chunk_size(); } for (const auto& reservation : startup_snapshot->Reservations()) { startup_total += reservation.chunk_size(); } PrintF("%10d bytes per isolate\n", startup_total); for (size_t i = 0; i < context_snapshots.size(); i++) { int context_total = 0; for (const auto& reservation : context_snapshots[i]->Reservations()) { context_total += reservation.chunk_size(); } PrintF("%10d bytes per context #%zu\n", context_total, i); } } } v8::StartupData Snapshot::CreateSnapshotBlob( const SnapshotData* startup_snapshot_in, const SnapshotData* read_only_snapshot_in, const std::vector<SnapshotData*>& context_snapshots_in, bool can_be_rehashed) { // Have these separate from snapshot_in for compression, since we need to // access the compressed data as well as the uncompressed reservations. const SnapshotData* startup_snapshot; const SnapshotData* read_only_snapshot; const std::vector<SnapshotData*>* context_snapshots; #ifdef V8_SNAPSHOT_COMPRESSION SnapshotData startup_compressed( SnapshotCompression::Compress(startup_snapshot_in)); SnapshotData read_only_compressed( SnapshotCompression::Compress(read_only_snapshot_in)); startup_snapshot = &startup_compressed; read_only_snapshot = &read_only_compressed; std::vector<SnapshotData> context_snapshots_compressed; context_snapshots_compressed.reserve(context_snapshots_in.size()); std::vector<SnapshotData*> context_snapshots_compressed_ptrs; for (unsigned int i = 0; i < context_snapshots_in.size(); ++i) { context_snapshots_compressed.push_back( SnapshotCompression::Compress(context_snapshots_in[i])); context_snapshots_compressed_ptrs.push_back( &context_snapshots_compressed[i]); } context_snapshots = &context_snapshots_compressed_ptrs; #else startup_snapshot = startup_snapshot_in; read_only_snapshot = read_only_snapshot_in; context_snapshots = &context_snapshots_in; #endif uint32_t num_contexts = static_cast<uint32_t>(context_snapshots->size()); uint32_t startup_snapshot_offset = SnapshotImpl::StartupSnapshotOffset(num_contexts); uint32_t total_length = startup_snapshot_offset; total_length += static_cast<uint32_t>(startup_snapshot->RawData().length()); total_length += static_cast<uint32_t>(read_only_snapshot->RawData().length()); for (const auto context_snapshot : *context_snapshots) { total_length += static_cast<uint32_t>(context_snapshot->RawData().length()); } ProfileDeserialization(read_only_snapshot_in, startup_snapshot_in, context_snapshots_in); char* data = new char[total_length]; // Zero out pre-payload data. Part of that is only used for padding. memset(data, 0, SnapshotImpl::StartupSnapshotOffset(num_contexts)); SnapshotImpl::SetHeaderValue(data, SnapshotImpl::kNumberOfContextsOffset, num_contexts); SnapshotImpl::SetHeaderValue(data, SnapshotImpl::kRehashabilityOffset, can_be_rehashed ? 1 : 0); // Write version string into snapshot data. memset(data + SnapshotImpl::kVersionStringOffset, 0, SnapshotImpl::kVersionStringLength); Version::GetString(Vector<char>(data + SnapshotImpl::kVersionStringOffset, SnapshotImpl::kVersionStringLength)); // Startup snapshot (isolate-specific data). uint32_t payload_offset = startup_snapshot_offset; uint32_t payload_length = static_cast<uint32_t>(startup_snapshot->RawData().length()); CopyBytes(data + payload_offset, reinterpret_cast<const char*>(startup_snapshot->RawData().begin()), payload_length); if (FLAG_profile_deserialization) { PrintF("Snapshot blob consists of:\n%10d bytes in %d chunks for startup\n", payload_length, static_cast<uint32_t>(startup_snapshot_in->Reservations().size())); } payload_offset += payload_length; // Read-only. SnapshotImpl::SetHeaderValue(data, SnapshotImpl::kReadOnlyOffsetOffset, payload_offset); payload_length = read_only_snapshot->RawData().length(); CopyBytes( data + payload_offset, reinterpret_cast<const char*>(read_only_snapshot->RawData().begin()), payload_length); if (FLAG_profile_deserialization) { PrintF("%10d bytes for read-only\n", payload_length); } payload_offset += payload_length; // Context snapshots (context-specific data). for (uint32_t i = 0; i < num_contexts; i++) { SnapshotImpl::SetHeaderValue( data, SnapshotImpl::ContextSnapshotOffsetOffset(i), payload_offset); SnapshotData* context_snapshot = (*context_snapshots)[i]; payload_length = context_snapshot->RawData().length(); CopyBytes( data + payload_offset, reinterpret_cast<const char*>(context_snapshot->RawData().begin()), payload_length); if (FLAG_profile_deserialization) { PrintF( "%10d bytes in %d chunks for context #%d\n", payload_length, static_cast<uint32_t>(context_snapshots_in[i]->Reservations().size()), i); } payload_offset += payload_length; } DCHECK_EQ(total_length, payload_offset); v8::StartupData result = {data, static_cast<int>(total_length)}; SnapshotImpl::SetHeaderValue( data, SnapshotImpl::kChecksumOffset, Checksum(SnapshotImpl::ChecksummedContent(&result))); return result; } uint32_t SnapshotImpl::ExtractNumContexts(const v8::StartupData* data) { CHECK_LT(kNumberOfContextsOffset, data->raw_size); uint32_t num_contexts = GetHeaderValue(data, kNumberOfContextsOffset); return num_contexts; } bool Snapshot::VerifyChecksum(const v8::StartupData* data) { base::ElapsedTimer timer; if (FLAG_profile_deserialization) timer.Start(); uint32_t expected = SnapshotImpl::GetHeaderValue(data, SnapshotImpl::kChecksumOffset); uint32_t result = Checksum(SnapshotImpl::ChecksummedContent(data)); if (FLAG_profile_deserialization) { double ms = timer.Elapsed().InMillisecondsF(); PrintF("[Verifying snapshot checksum took %0.3f ms]\n", ms); } return result == expected; } uint32_t SnapshotImpl::ExtractContextOffset(const v8::StartupData* data, uint32_t index) { // Extract the offset of the context at a given index from the StartupData, // and check that it is within bounds. uint32_t context_offset = GetHeaderValue(data, ContextSnapshotOffsetOffset(index)); CHECK_LT(context_offset, static_cast<uint32_t>(data->raw_size)); return context_offset; } bool Snapshot::ExtractRehashability(const v8::StartupData* data) { CHECK_LT(SnapshotImpl::kRehashabilityOffset, static_cast<uint32_t>(data->raw_size)); uint32_t rehashability = SnapshotImpl::GetHeaderValue(data, SnapshotImpl::kRehashabilityOffset); CHECK_IMPLIES(rehashability != 0, rehashability == 1); return rehashability != 0; } namespace { Vector<const byte> ExtractData(const v8::StartupData* snapshot, uint32_t start_offset, uint32_t end_offset) { CHECK_LT(start_offset, end_offset); CHECK_LT(end_offset, snapshot->raw_size); uint32_t length = end_offset - start_offset; const byte* data = reinterpret_cast<const byte*>(snapshot->data + start_offset); return Vector<const byte>(data, length); } } // namespace Vector<const byte> SnapshotImpl::ExtractStartupData( const v8::StartupData* data) { DCHECK(Snapshot::SnapshotIsValid(data)); uint32_t num_contexts = ExtractNumContexts(data); return ExtractData(data, StartupSnapshotOffset(num_contexts), GetHeaderValue(data, kReadOnlyOffsetOffset)); } Vector<const byte> SnapshotImpl::ExtractReadOnlyData( const v8::StartupData* data) { DCHECK(Snapshot::SnapshotIsValid(data)); return ExtractData(data, GetHeaderValue(data, kReadOnlyOffsetOffset), GetHeaderValue(data, ContextSnapshotOffsetOffset(0))); } Vector<const byte> SnapshotImpl::ExtractContextData(const v8::StartupData* data, uint32_t index) { uint32_t num_contexts = ExtractNumContexts(data); CHECK_LT(index, num_contexts); uint32_t context_offset = ExtractContextOffset(data, index); uint32_t next_context_offset; if (index == num_contexts - 1) { next_context_offset = data->raw_size; } else { next_context_offset = ExtractContextOffset(data, index + 1); CHECK_LT(next_context_offset, data->raw_size); } const byte* context_data = reinterpret_cast<const byte*>(data->data + context_offset); uint32_t context_length = next_context_offset - context_offset; return Vector<const byte>(context_data, context_length); } void SnapshotImpl::CheckVersion(const v8::StartupData* data) { char version[kVersionStringLength]; memset(version, 0, kVersionStringLength); CHECK_LT(kVersionStringOffset + kVersionStringLength, static_cast<uint32_t>(data->raw_size)); Version::GetString(Vector<char>(version, kVersionStringLength)); if (strncmp(version, data->data + kVersionStringOffset, kVersionStringLength) != 0) { FATAL( "Version mismatch between V8 binary and snapshot.\n" "# V8 binary version: %.*s\n" "# Snapshot version: %.*s\n" "# The snapshot consists of %d bytes and contains %d context(s).", kVersionStringLength, version, kVersionStringLength, data->data + kVersionStringOffset, data->raw_size, ExtractNumContexts(data)); } } namespace { bool RunExtraCode(v8::Isolate* isolate, v8::Local<v8::Context> context, const char* utf8_source, const char* name) { v8::Context::Scope context_scope(context); v8::TryCatch try_catch(isolate); v8::Local<v8::String> source_string; if (!v8::String::NewFromUtf8(isolate, utf8_source).ToLocal(&source_string)) { return false; } v8::Local<v8::String> resource_name = v8::String::NewFromUtf8(isolate, name).ToLocalChecked(); v8::ScriptOrigin origin(resource_name); v8::ScriptCompiler::Source source(source_string, origin); v8::Local<v8::Script> script; if (!v8::ScriptCompiler::Compile(context, &source).ToLocal(&script)) return false; if (script->Run(context).IsEmpty()) return false; CHECK(!try_catch.HasCaught()); return true; } } // namespace v8::StartupData CreateSnapshotDataBlobInternal( v8::SnapshotCreator::FunctionCodeHandling function_code_handling, const char* embedded_source, v8::Isolate* isolate) { // If no isolate is passed in, create it (and a new context) from scratch. if (isolate == nullptr) isolate = v8::Isolate::Allocate(); // Optionally run a script to embed, and serialize to create a snapshot blob. v8::SnapshotCreator snapshot_creator(isolate); { v8::HandleScope scope(isolate); v8::Local<v8::Context> context = v8::Context::New(isolate); if (embedded_source != nullptr && !RunExtraCode(isolate, context, embedded_source, "<embedded>")) { return {}; } snapshot_creator.SetDefaultContext(context); } return snapshot_creator.CreateBlob(function_code_handling); } v8::StartupData WarmUpSnapshotDataBlobInternal( v8::StartupData cold_snapshot_blob, const char* warmup_source) { CHECK(cold_snapshot_blob.raw_size > 0 && cold_snapshot_blob.data != nullptr); CHECK_NOT_NULL(warmup_source); // Use following steps to create a warmed up snapshot blob from a cold one: // - Create a new isolate from the cold snapshot. // - Create a new context to run the warmup script. This will trigger // compilation of executed functions. // - Create a new context. This context will be unpolluted. // - Serialize the isolate and the second context into a new snapshot blob. v8::SnapshotCreator snapshot_creator(nullptr, &cold_snapshot_blob); v8::Isolate* isolate = snapshot_creator.GetIsolate(); { v8::HandleScope scope(isolate); v8::Local<v8::Context> context = v8::Context::New(isolate); if (!RunExtraCode(isolate, context, warmup_source, "<warm-up>")) { return {}; } } { v8::HandleScope handle_scope(isolate); isolate->ContextDisposedNotification(false); v8::Local<v8::Context> context = v8::Context::New(isolate); snapshot_creator.SetDefaultContext(context); } return snapshot_creator.CreateBlob( v8::SnapshotCreator::FunctionCodeHandling::kKeep); } } // namespace internal } // namespace v8