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      1 // Copyright 2006-2008 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // The common functionality when building with or without snapshots.
      6 
      7 #include "src/snapshot/snapshot.h"
      8 
      9 #include "src/api.h"
     10 #include "src/base/platform/platform.h"
     11 #include "src/full-codegen/full-codegen.h"
     12 
     13 namespace v8 {
     14 namespace internal {
     15 
     16 #ifdef DEBUG
     17 bool Snapshot::SnapshotIsValid(v8::StartupData* snapshot_blob) {
     18   return !Snapshot::ExtractStartupData(snapshot_blob).is_empty() &&
     19          !Snapshot::ExtractContextData(snapshot_blob).is_empty();
     20 }
     21 #endif  // DEBUG
     22 
     23 
     24 bool Snapshot::HaveASnapshotToStartFrom(Isolate* isolate) {
     25   // Do not use snapshots if the isolate is used to create snapshots.
     26   return isolate->snapshot_blob() != NULL &&
     27          isolate->snapshot_blob()->data != NULL;
     28 }
     29 
     30 
     31 bool Snapshot::EmbedsScript(Isolate* isolate) {
     32   if (!isolate->snapshot_available()) return false;
     33   return ExtractMetadata(isolate->snapshot_blob()).embeds_script();
     34 }
     35 
     36 
     37 uint32_t Snapshot::SizeOfFirstPage(Isolate* isolate, AllocationSpace space) {
     38   DCHECK(space >= FIRST_PAGED_SPACE && space <= LAST_PAGED_SPACE);
     39   if (!isolate->snapshot_available()) {
     40     return static_cast<uint32_t>(MemoryAllocator::PageAreaSize(space));
     41   }
     42   uint32_t size;
     43   int offset = kFirstPageSizesOffset + (space - FIRST_PAGED_SPACE) * kInt32Size;
     44   memcpy(&size, isolate->snapshot_blob()->data + offset, kInt32Size);
     45   return size;
     46 }
     47 
     48 
     49 bool Snapshot::Initialize(Isolate* isolate) {
     50   if (!isolate->snapshot_available()) return false;
     51   base::ElapsedTimer timer;
     52   if (FLAG_profile_deserialization) timer.Start();
     53 
     54   const v8::StartupData* blob = isolate->snapshot_blob();
     55   Vector<const byte> startup_data = ExtractStartupData(blob);
     56   SnapshotData snapshot_data(startup_data);
     57   Deserializer deserializer(&snapshot_data);
     58   bool success = isolate->Init(&deserializer);
     59   if (FLAG_profile_deserialization) {
     60     double ms = timer.Elapsed().InMillisecondsF();
     61     int bytes = startup_data.length();
     62     PrintF("[Deserializing isolate (%d bytes) took %0.3f ms]\n", bytes, ms);
     63   }
     64   return success;
     65 }
     66 
     67 
     68 MaybeHandle<Context> Snapshot::NewContextFromSnapshot(
     69     Isolate* isolate, Handle<JSGlobalProxy> global_proxy) {
     70   if (!isolate->snapshot_available()) return Handle<Context>();
     71   base::ElapsedTimer timer;
     72   if (FLAG_profile_deserialization) timer.Start();
     73 
     74   const v8::StartupData* blob = isolate->snapshot_blob();
     75   Vector<const byte> context_data = ExtractContextData(blob);
     76   SnapshotData snapshot_data(context_data);
     77   Deserializer deserializer(&snapshot_data);
     78 
     79   MaybeHandle<Object> maybe_context =
     80       deserializer.DeserializePartial(isolate, global_proxy);
     81   Handle<Object> result;
     82   if (!maybe_context.ToHandle(&result)) return MaybeHandle<Context>();
     83   CHECK(result->IsContext());
     84   if (FLAG_profile_deserialization) {
     85     double ms = timer.Elapsed().InMillisecondsF();
     86     int bytes = context_data.length();
     87     PrintF("[Deserializing context (%d bytes) took %0.3f ms]\n", bytes, ms);
     88   }
     89   return Handle<Context>::cast(result);
     90 }
     91 
     92 
     93 void CalculateFirstPageSizes(bool is_default_snapshot,
     94                              const SnapshotData& startup_snapshot,
     95                              const SnapshotData& context_snapshot,
     96                              uint32_t* sizes_out) {
     97   Vector<const SerializedData::Reservation> startup_reservations =
     98       startup_snapshot.Reservations();
     99   Vector<const SerializedData::Reservation> context_reservations =
    100       context_snapshot.Reservations();
    101   int startup_index = 0;
    102   int context_index = 0;
    103 
    104   if (FLAG_profile_deserialization) {
    105     int startup_total = 0;
    106     int context_total = 0;
    107     for (auto& reservation : startup_reservations) {
    108       startup_total += reservation.chunk_size();
    109     }
    110     for (auto& reservation : context_reservations) {
    111       context_total += reservation.chunk_size();
    112     }
    113     PrintF(
    114         "Deserialization will reserve:\n"
    115         "%10d bytes per isolate\n"
    116         "%10d bytes per context\n",
    117         startup_total, context_total);
    118   }
    119 
    120   for (int space = 0; space < i::Serializer::kNumberOfSpaces; space++) {
    121     bool single_chunk = true;
    122     while (!startup_reservations[startup_index].is_last()) {
    123       single_chunk = false;
    124       startup_index++;
    125     }
    126     while (!context_reservations[context_index].is_last()) {
    127       single_chunk = false;
    128       context_index++;
    129     }
    130 
    131     uint32_t required = kMaxUInt32;
    132     if (single_chunk) {
    133       // If both the startup snapshot data and the context snapshot data on
    134       // this space fit in a single page, then we consider limiting the size
    135       // of the first page. For this, we add the chunk sizes and some extra
    136       // allowance. This way we achieve a smaller startup memory footprint.
    137       required = (startup_reservations[startup_index].chunk_size() +
    138                   2 * context_reservations[context_index].chunk_size()) +
    139                  Page::kObjectStartOffset;
    140       // Add a small allowance to the code space for small scripts.
    141       if (space == CODE_SPACE) required += 32 * KB;
    142     } else {
    143       // We expect the vanilla snapshot to only require on page per space.
    144       DCHECK(!is_default_snapshot);
    145     }
    146 
    147     if (space >= FIRST_PAGED_SPACE && space <= LAST_PAGED_SPACE) {
    148       uint32_t max_size =
    149           MemoryAllocator::PageAreaSize(static_cast<AllocationSpace>(space));
    150       sizes_out[space - FIRST_PAGED_SPACE] = Min(required, max_size);
    151     } else {
    152       DCHECK(single_chunk);
    153     }
    154     startup_index++;
    155     context_index++;
    156   }
    157 
    158   DCHECK_EQ(startup_reservations.length(), startup_index);
    159   DCHECK_EQ(context_reservations.length(), context_index);
    160 }
    161 
    162 
    163 v8::StartupData Snapshot::CreateSnapshotBlob(
    164     const i::StartupSerializer& startup_ser,
    165     const i::PartialSerializer& context_ser, Snapshot::Metadata metadata) {
    166   SnapshotData startup_snapshot(startup_ser);
    167   SnapshotData context_snapshot(context_ser);
    168   Vector<const byte> startup_data = startup_snapshot.RawData();
    169   Vector<const byte> context_data = context_snapshot.RawData();
    170 
    171   uint32_t first_page_sizes[kNumPagedSpaces];
    172 
    173   CalculateFirstPageSizes(!metadata.embeds_script(), startup_snapshot,
    174                           context_snapshot, first_page_sizes);
    175 
    176   int startup_length = startup_data.length();
    177   int context_length = context_data.length();
    178   int context_offset = ContextOffset(startup_length);
    179 
    180   int length = context_offset + context_length;
    181   char* data = new char[length];
    182 
    183   memcpy(data + kMetadataOffset, &metadata.RawValue(), kInt32Size);
    184   memcpy(data + kFirstPageSizesOffset, first_page_sizes,
    185          kNumPagedSpaces * kInt32Size);
    186   memcpy(data + kStartupLengthOffset, &startup_length, kInt32Size);
    187   memcpy(data + kStartupDataOffset, startup_data.begin(), startup_length);
    188   memcpy(data + context_offset, context_data.begin(), context_length);
    189   v8::StartupData result = {data, length};
    190 
    191   if (FLAG_profile_deserialization) {
    192     PrintF(
    193         "Snapshot blob consists of:\n"
    194         "%10d bytes for startup\n"
    195         "%10d bytes for context\n",
    196         startup_length, context_length);
    197   }
    198   return result;
    199 }
    200 
    201 
    202 Snapshot::Metadata Snapshot::ExtractMetadata(const v8::StartupData* data) {
    203   uint32_t raw;
    204   memcpy(&raw, data->data + kMetadataOffset, kInt32Size);
    205   return Metadata(raw);
    206 }
    207 
    208 
    209 Vector<const byte> Snapshot::ExtractStartupData(const v8::StartupData* data) {
    210   DCHECK_LT(kIntSize, data->raw_size);
    211   int startup_length;
    212   memcpy(&startup_length, data->data + kStartupLengthOffset, kInt32Size);
    213   DCHECK_LT(startup_length, data->raw_size);
    214   const byte* startup_data =
    215       reinterpret_cast<const byte*>(data->data + kStartupDataOffset);
    216   return Vector<const byte>(startup_data, startup_length);
    217 }
    218 
    219 
    220 Vector<const byte> Snapshot::ExtractContextData(const v8::StartupData* data) {
    221   DCHECK_LT(kIntSize, data->raw_size);
    222   int startup_length;
    223   memcpy(&startup_length, data->data + kStartupLengthOffset, kIntSize);
    224   int context_offset = ContextOffset(startup_length);
    225   const byte* context_data =
    226       reinterpret_cast<const byte*>(data->data + context_offset);
    227   DCHECK_LT(context_offset, data->raw_size);
    228   int context_length = data->raw_size - context_offset;
    229   return Vector<const byte>(context_data, context_length);
    230 }
    231 }  // namespace internal
    232 }  // namespace v8
    233