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// 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/partial-deserializer.h"
#include "src/snapshot/read-only-deserializer.h"
#include "src/snapshot/startup-deserializer.h"
#include "src/utils/memcopy.h"
#include "src/utils/version.h"
namespace v8 {
namespace internal {
#ifdef DEBUG
bool Snapshot::SnapshotIsValid(const v8::StartupData* snapshot_blob) {
return Snapshot::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>(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();
CheckVersion(blob);
CHECK(VerifyChecksum(blob));
Vector<const byte> startup_data = ExtractStartupData(blob);
SnapshotData startup_snapshot_data(startup_data);
Vector<const byte> read_only_data = ExtractReadOnlyData(blob);
SnapshotData read_only_snapshot_data(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 =
ExtractContextData(blob, static_cast<uint32_t>(context_index));
SnapshotData snapshot_data(context_data);
MaybeHandle<Context> maybe_result = PartialDeserializer::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,
const SnapshotData* read_only_snapshot,
const std::vector<SnapshotData*>& context_snapshots, bool can_be_rehashed) {
uint32_t num_contexts = static_cast<uint32_t>(context_snapshots.size());
uint32_t startup_snapshot_offset = StartupSnapshotOffset(num_contexts);
uint32_t total_length = startup_snapshot_offset;
DCHECK(IsAligned(total_length, kPointerAlignment));
total_length += static_cast<uint32_t>(startup_snapshot->RawData().length());
DCHECK(IsAligned(total_length, kPointerAlignment));
total_length += static_cast<uint32_t>(read_only_snapshot->RawData().length());
DCHECK(IsAligned(total_length, kPointerAlignment));
for (const auto context_snapshot : context_snapshots) {
total_length += static_cast<uint32_t>(context_snapshot->RawData().length());
DCHECK(IsAligned(total_length, kPointerAlignment));
}
ProfileDeserialization(read_only_snapshot, startup_snapshot,
context_snapshots);
char* data = new char[total_length];
// Zero out pre-payload data. Part of that is only used for padding.
memset(data, 0, StartupSnapshotOffset(num_contexts));
SetHeaderValue(data, kNumberOfContextsOffset, num_contexts);
SetHeaderValue(data, kRehashabilityOffset, can_be_rehashed ? 1 : 0);
// Write version string into snapshot data.
memset(data + kVersionStringOffset, 0, kVersionStringLength);
Version::GetString(
Vector<char>(data + kVersionStringOffset, 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->Reservations().size()));
}
payload_offset += payload_length;
// Read-only.
SetHeaderValue(data, 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;
// Partial snapshots (context-specific data).
for (uint32_t i = 0; i < num_contexts; i++) {
SetHeaderValue(data, 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_snapshot->Reservations().size()), i);
}
payload_offset += payload_length;
}
DCHECK_EQ(total_length, payload_offset);
v8::StartupData result = {data, static_cast<int>(total_length)};
Checksum checksum(ChecksummedContent(&result));
SetHeaderValue(data, kChecksumPartAOffset, checksum.a());
SetHeaderValue(data, kChecksumPartBOffset, checksum.b());
return result;
}
uint32_t Snapshot::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_a = GetHeaderValue(data, kChecksumPartAOffset);
uint32_t expected_b = GetHeaderValue(data, kChecksumPartBOffset);
Checksum checksum(ChecksummedContent(data));
if (FLAG_profile_deserialization) {
double ms = timer.Elapsed().InMillisecondsF();
PrintF("[Verifying snapshot checksum took %0.3f ms]\n", ms);
}
return checksum.Check(expected_a, expected_b);
}
uint32_t Snapshot::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(kRehashabilityOffset, static_cast<uint32_t>(data->raw_size));
uint32_t rehashability = GetHeaderValue(data, 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> Snapshot::ExtractStartupData(const v8::StartupData* data) {
DCHECK(SnapshotIsValid(data));
uint32_t num_contexts = ExtractNumContexts(data);
return ExtractData(data, StartupSnapshotOffset(num_contexts),
GetHeaderValue(data, kReadOnlyOffsetOffset));
}
Vector<const byte> Snapshot::ExtractReadOnlyData(const v8::StartupData* data) {
DCHECK(SnapshotIsValid(data));
return ExtractData(data, GetHeaderValue(data, kReadOnlyOffsetOffset),
GetHeaderValue(data, ContextSnapshotOffsetOffset(0)));
}
Vector<const byte> Snapshot::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 Snapshot::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));
}
}
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());
DCHECK(IsAligned(size, kPointerAlignment));
// 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 {
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, v8::NewStringType::kNormal)
.ToLocal(&source_string)) {
return false;
}
v8::Local<v8::String> resource_name =
v8::String::NewFromUtf8(isolate, name, v8::NewStringType::kNormal)
.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