[static-roots] Support serializing read-only heap as a memory dump

Build mode for serializing the read only heap as a memory dump in the
startup snapshot. This makes compressed pointers of root objects
statically known at mksnapshot time.

This CL also adds a feature to mksnapshot to dump the static addresses
to a C++ header file. This will allow us to use these addresses in the
future.

The mode is disabled for now since we need some build infrastructure
first to conveniently re-generate the table when the layout changes.

Bug: v8:13466
Change-Id: I975b15bd89fedf713fb7d12b4929935ece78139d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4056181
Commit-Queue: Olivier Flückiger <olivf@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#84815}

BUILD.bazel

@@ -2036,6 +2036,7 @@ filegroup(
         "src/roots/roots-inl.h",
         "src/roots/roots.cc",
         "src/roots/roots.h",
+        "src/roots/static-roots.h",
         "src/runtime/runtime-array.cc",
         "src/runtime/runtime-atomics.cc",
         "src/runtime/runtime-bigint.cc",
@@ -3234,6 +3235,8 @@ filegroup(
         "src/snapshot/embedded/platform-embedded-file-writer-mac.h",
         "src/snapshot/embedded/platform-embedded-file-writer-win.cc",
         "src/snapshot/embedded/platform-embedded-file-writer-win.h",
+        "src/snapshot/static-roots-gen.cc",
+        "src/snapshot/static-roots-gen.h",
         "src/snapshot/mksnapshot.cc",
         "src/snapshot/snapshot-empty.cc",
     ],

BUILD.gn

@@ -3508,6 +3508,7 @@ v8_header_set("v8_internal_headers") {
     "src/regexp/special-case.h",
     "src/roots/roots-inl.h",
     "src/roots/roots.h",
+    "src/roots/static-roots.h",
     "src/runtime/runtime-utils.h",
     "src/runtime/runtime.h",
     "src/sandbox/bounded-size-inl.h",
@@ -6227,6 +6228,8 @@ if (current_toolchain == v8_snapshot_toolchain) {
       "src/snapshot/embedded/platform-embedded-file-writer-win.h",
       "src/snapshot/mksnapshot.cc",
       "src/snapshot/snapshot-empty.cc",
+      "src/snapshot/static-roots-gen.cc",
+      "src/snapshot/static-roots-gen.h",
     ]
 
     if (v8_control_flow_integrity) {

src/common/globals.h

@@ -122,6 +122,17 @@ namespace internal {
 #define V8_CAN_CREATE_SHARED_HEAP_BOOL false
 #endif
 
+// Disabling WASM or INTL invalidates the contents of static-roots.h
+#if defined(V8_SHARED_RO_HEAP) && defined(V8_COMPRESS_POINTERS) &&           \
+    defined(V8_COMPRESS_POINTERS_IN_SHARED_CAGE) && V8_ENABLE_WEBASSEMBLY && \
+    defined(V8_INTL_SUPPORT)
+// TODO(olivf, v8:13466): Add build infra to conveniently re-regenerate the
+// static roots table and then enable it.
+#define V8_STATIC_ROOTS_BOOL false
+#else
+#define V8_STATIC_ROOTS_BOOL false
+#endif
+
 #ifdef V8_ENABLE_SANDBOX
 #define V8_ENABLE_SANDBOX_BOOL true
 #else

src/execution/isolate.cc

@@ -34,6 +34,7 @@
 #include "src/codegen/compilation-cache.h"
 #include "src/codegen/flush-instruction-cache.h"
 #include "src/common/assert-scope.h"
+#include "src/common/globals.h"
 #include "src/common/ptr-compr-inl.h"
 #include "src/compiler-dispatcher/lazy-compile-dispatcher.h"
 #include "src/compiler-dispatcher/optimizing-compile-dispatcher.h"
@@ -99,6 +100,7 @@
 #include "src/profiler/heap-profiler.h"
 #include "src/profiler/tracing-cpu-profiler.h"
 #include "src/regexp/regexp-stack.h"
+#include "src/roots/static-roots.h"
 #include "src/snapshot/embedded/embedded-data-inl.h"
 #include "src/snapshot/embedded/embedded-file-writer-interface.h"
 #include "src/snapshot/read-only-deserializer.h"
@@ -423,6 +425,20 @@ size_t Isolate::HashIsolateForEmbeddedBlob() {
   static constexpr size_t kSeed = 0;
   size_t hash = kSeed;
 
+  // Hash static entries of the roots table.
+  hash = base::hash_combine(hash, V8_STATIC_ROOTS_BOOL);
+#if V8_STATIC_ROOTS_BOOL
+  hash = base::hash_combine(hash,
+                            static_cast<int>(RootIndex::kReadOnlyRootsCount));
+  RootIndex i = RootIndex::kFirstReadOnlyRoot;
+  for (auto ptr : StaticReadOnlyRootsPointerTable) {
+    hash = base::hash_combine(ptr, hash);
+    hash = base::hash_combine(std::hash<std::string>{}(roots_table().name(i)),
+                              hash);
+    ++i;
+  }
+#endif  // V8_STATIC_ROOTS_BOOL
+
   // Hash data sections of builtin code objects.
   for (Builtin builtin = Builtins::kFirst; builtin <= Builtins::kLast;
        ++builtin) {
@@ -4136,6 +4152,30 @@ VirtualMemoryCage* Isolate::GetPtrComprCodeCageForTesting() {
   return V8_EXTERNAL_CODE_SPACE_BOOL ? heap_.code_range() : GetPtrComprCage();
 }
 
+// If this check fails mksnapshot needs to be built without static roots and
+// then called with --static-roots to re-regenerate the static-roots.h file.
+void Isolate::VerifyStaticRoots() {
+#if V8_STATIC_ROOTS_BOOL
+  auto& roots = roots_table();
+  CHECK_EQ(static_cast<int>(RootIndex::kReadOnlyRootsCount),
+           StaticReadOnlyRootsPointerTable.size());
+  RootIndex idx = RootIndex::kFirstReadOnlyRoot;
+  ReadOnlyPage* first_page = read_only_heap()->read_only_space()->pages()[0];
+  for (Tagged_t cmp_ptr : StaticReadOnlyRootsPointerTable) {
+    Address the_root = roots[idx];
+    Address ptr =
+        V8HeapCompressionScheme::DecompressTaggedPointer(cage_base(), cmp_ptr);
+    CHECK_EQ(the_root, ptr);
+    // All roots must fit on first page, since only this page is guaranteed to
+    // have a stable offset from the cage base. If this ever changes we need
+    // to load more pages with predictable offset at
+    // ReadOnlySpace::InitFromMemoryDump.
+    CHECK(first_page->Contains(the_root));
+    ++idx;
+  }
+#endif  // V8_STATIC_ROOTS_BOOL
+}
+
 bool Isolate::Init(SnapshotData* startup_snapshot_data,
                    SnapshotData* read_only_snapshot_data,
                    SnapshotData* shared_heap_snapshot_data, bool can_rehash) {
@@ -4482,6 +4522,7 @@ bool Isolate::Init(SnapshotData* startup_snapshot_data,
                                                can_rehash);
       startup_deserializer.DeserializeIntoIsolate();
     }
+    if (DEBUG_BOOL) VerifyStaticRoots();
     load_stub_cache_->Initialize();
     store_stub_cache_->Initialize();
     interpreter_->Initialize();

src/execution/isolate.h

@@ -2040,6 +2040,8 @@ class V8_EXPORT_PRIVATE Isolate final : private HiddenFactory {
   Object LocalsBlockListCacheGet(Handle<ScopeInfo> scope_info);
 
  private:
+  void VerifyStaticRoots();
+
   explicit Isolate(std::unique_ptr<IsolateAllocator> isolate_allocator,
                    bool is_shared);
   ~Isolate();

src/flags/flag-definitions.h

@@ -2001,6 +2001,8 @@ DEFINE_STRING(embedded_src, nullptr,
 DEFINE_STRING(
     embedded_variant, nullptr,
     "Label to disambiguate symbols in embedded data file. (mksnapshot only)")
+DEFINE_STRING(static_roots, nullptr,
+              "Path for writing static-roots.h. (mksnapshot only)")
 DEFINE_STRING(startup_src, nullptr,
               "Write V8 startup as C++ src. (mksnapshot only)")
 DEFINE_STRING(startup_blob, nullptr,

src/heap/memory-allocator.cc

@@ -345,26 +345,28 @@ size_t MemoryAllocator::ComputeChunkSize(size_t area_size,
 }
 
 base::Optional<MemoryAllocator::MemoryChunkAllocationResult>
-MemoryAllocator::AllocateUninitializedChunk(BaseSpace* space, size_t area_size,
+MemoryAllocator::AllocateUninitializedChunkAt(BaseSpace* space,
+                                              size_t area_size,
                                               Executability executable,
+                                              Address hint,
                                               PageSize page_size) {
-#ifdef V8_COMPRESS_POINTERS
+#ifndef V8_COMPRESS_POINTERS
   // When pointer compression is enabled, spaces are expected to be at a
   // predictable address (see mkgrokdump) so we don't supply a hint and rely on
   // the deterministic behaviour of the BoundedPageAllocator.
-  void* address_hint = nullptr;
-#else
-  void* address_hint = AlignedAddress(isolate_->heap()->GetRandomMmapAddr(),
-                                      MemoryChunk::kAlignment);
+  if (hint == kNullAddress) {
+    hint = reinterpret_cast<Address>(AlignedAddress(
+        isolate_->heap()->GetRandomMmapAddr(), MemoryChunk::kAlignment));
+  }
 #endif
 
   VirtualMemory reservation;
   size_t chunk_size = ComputeChunkSize(area_size, executable);
   DCHECK_EQ(chunk_size % GetCommitPageSize(), 0);
 
-  Address base =
-      AllocateAlignedMemory(chunk_size, area_size, MemoryChunk::kAlignment,
-                            executable, address_hint, &reservation);
+  Address base = AllocateAlignedMemory(
+      chunk_size, area_size, MemoryChunk::kAlignment, executable,
+      reinterpret_cast<void*>(hint), &reservation);
   if (base == kNullAddress) return {};
 
   size_ += reservation.size();
@@ -587,11 +589,12 @@ Page* MemoryAllocator::AllocatePage(MemoryAllocator::AllocationMode alloc_mode,
   return page;
 }
 
-ReadOnlyPage* MemoryAllocator::AllocateReadOnlyPage(ReadOnlySpace* space) {
+ReadOnlyPage* MemoryAllocator::AllocateReadOnlyPage(ReadOnlySpace* space,
+                                                    Address hint) {
   DCHECK_EQ(space->identity(), RO_SPACE);
   size_t size = MemoryChunkLayout::AllocatableMemoryInMemoryChunk(RO_SPACE);
   base::Optional<MemoryChunkAllocationResult> chunk_info =
-      AllocateUninitializedChunk(space, size, NOT_EXECUTABLE,
+      AllocateUninitializedChunkAt(space, size, NOT_EXECUTABLE, hint,
                                    PageSize::kRegular);
   if (!chunk_info) return nullptr;
   return new (chunk_info->start) ReadOnlyPage(

src/heap/memory-allocator.h

@@ -194,7 +194,8 @@ class MemoryAllocator {
                                                  size_t object_size,
                                                  Executability executable);
 
-  ReadOnlyPage* AllocateReadOnlyPage(ReadOnlySpace* space);
+  ReadOnlyPage* AllocateReadOnlyPage(ReadOnlySpace* space,
+                                     Address hint = kNullAddress);
 
   std::unique_ptr<::v8::PageAllocator::SharedMemoryMapping> RemapSharedPage(
       ::v8::PageAllocator::SharedMemory* shared_memory, Address new_address);
@@ -293,7 +294,14 @@ class MemoryAllocator {
   // the unintialized memory region.
   V8_WARN_UNUSED_RESULT base::Optional<MemoryChunkAllocationResult>
   AllocateUninitializedChunk(BaseSpace* space, size_t area_size,
-                             Executability executable, PageSize page_size);
+                             Executability executable, PageSize page_size) {
+    return AllocateUninitializedChunkAt(space, area_size, executable,
+                                        kNullAddress, page_size);
+  }
+  V8_WARN_UNUSED_RESULT base::Optional<MemoryChunkAllocationResult>
+  AllocateUninitializedChunkAt(BaseSpace* space, size_t area_size,
+                               Executability executable, Address hint,
+                               PageSize page_size);
 
   // Internal raw allocation method that allocates an aligned MemoryChunk and
   // sets the right memory permissions.

src/heap/read-only-spaces.cc

@@ -21,6 +21,7 @@
 #include "src/heap/read-only-heap.h"
 #include "src/objects/objects-inl.h"
 #include "src/snapshot/snapshot-data.h"
+#include "src/snapshot/snapshot-source-sink.h"
 #include "src/snapshot/snapshot-utils.h"
 
 namespace v8 {
@@ -754,5 +755,46 @@ SharedReadOnlySpace::SharedReadOnlySpace(Heap* heap,
   pages_ = artifacts->pages();
 }
 
+void ReadOnlySpace::InitFromMemoryDump(Isolate* isolate,
+                                       SnapshotByteSource* in) {
+  size_t num_pages = in->GetInt();
+  auto cage = isolate->GetPtrComprCage();
+
+  CHECK_LT(num_pages, 10);
+
+  auto first_page = cage->base() + in->GetInt();
+
+  for (size_t i = 0; i < num_pages; ++i) {
+    int size = in->GetInt();
+    ReadOnlyPage* chunk;
+    if (i == 0) {
+      chunk =
+          heap()->memory_allocator()->AllocateReadOnlyPage(this, first_page);
+      // If this fails we probably allocated r/o space too late.
+      CHECK_EQ(reinterpret_cast<void*>(first_page), chunk);
+    } else {
+      chunk = heap()->memory_allocator()->AllocateReadOnlyPage(this);
+    }
+
+    capacity_ += AreaSize();
+
+    AccountCommitted(chunk->size());
+    CHECK_NOT_NULL(chunk);
+
+    CHECK_LE(chunk->area_start() + size, chunk->area_end());
+    in->CopyRaw(reinterpret_cast<void*>(chunk->area_start()), size);
+    chunk->IncreaseAllocatedBytes(size);
+    chunk->high_water_mark_ = (chunk->area_start() - chunk->address()) + size;
+
+    DCHECK_NE(chunk->allocated_bytes(), 0);
+    accounting_stats_.IncreaseCapacity(chunk->area_size());
+    accounting_stats_.IncreaseAllocatedBytes(chunk->allocated_bytes(), chunk);
+    pages_.push_back(chunk);
+
+    top_ = chunk->area_start() + size;
+    limit_ = chunk->area_end();
+  }
+}
+
 }  // namespace internal
 }  // namespace v8

src/heap/read-only-spaces.h

@@ -23,7 +23,7 @@ namespace internal {
 
 class MemoryAllocator;
 class ReadOnlyHeap;
-class SnapshotData;
+class SnapshotByteSource;
 
 class ReadOnlyPage : public BasicMemoryChunk {
  public:
@@ -235,6 +235,8 @@ class ReadOnlySpace : public BaseSpace {
 
   Address FirstPageAddress() const { return pages_.front()->address(); }
 
+  void InitFromMemoryDump(Isolate* isolate, SnapshotByteSource* source);
+
  protected:
   friend class SingleCopyReadOnlyArtifacts;
 

src/heap/setup-heap-internal.cc

@@ -728,6 +728,20 @@ void Heap::CreateInitialReadOnlyObjects() {
   Factory* factory = isolate()->factory();
   ReadOnlyRoots roots(this);
 
+  // For static roots we need the r/o space to have identical layout on all
+  // compile targets. Varying objects are padded to their biggest size.
+  auto StaticRootsEnsureAllocatedSize = [&](HeapObject obj, int required) {
+#ifdef V8_STATIC_ROOTS_BOOL
+    if (required == obj.Size()) return;
+    CHECK_LT(obj.Size(), required);
+    int filler_size = required - obj.Size();
+    auto filler = factory->NewFillerObject(filler_size,
+                                           AllocationAlignment::kTaggedAligned,
+                                           AllocationType::kReadOnly);
+    CHECK_EQ(filler->address() + filler->Size(), obj.address() + required);
+#endif
+  };
+
   // The -0 value must be set before NewNumber works.
   set_minus_zero_value(
       *factory->NewHeapNumber<AllocationType::kReadOnly>(-0.0));
@@ -939,6 +953,8 @@ void Heap::CreateInitialReadOnlyObjects() {
   Handle<SwissNameDictionary> empty_swiss_property_dictionary =
       factory->CreateCanonicalEmptySwissNameDictionary();
   set_empty_swiss_property_dictionary(*empty_swiss_property_dictionary);
+  StaticRootsEnsureAllocatedSize(*empty_swiss_property_dictionary,
+                                 8 * kTaggedSize);
 
   // Allocate the empty FeedbackMetadata.
   Handle<FeedbackMetadata> empty_feedback_metadata =
@@ -959,8 +975,9 @@ void Heap::CreateInitialReadOnlyObjects() {
   set_native_scope_info(*native_scope_info);
 
   // Canonical off-heap trampoline data
-  set_off_heap_trampoline_relocation_info(
-      *Builtins::GenerateOffHeapTrampolineRelocInfo(isolate_));
+  auto reloc_info = Builtins::GenerateOffHeapTrampolineRelocInfo(isolate_);
+  set_off_heap_trampoline_relocation_info(*reloc_info);
+  StaticRootsEnsureAllocatedSize(*reloc_info, 4 * kTaggedSize);
 
   if (V8_EXTERNAL_CODE_SPACE_BOOL) {
     // These roots will not be used.

src/roots/roots.cc

@@ -4,9 +4,11 @@
 
 #include "src/roots/roots.h"
 
+#include "src/common/globals.h"
 #include "src/objects/elements-kind.h"
 #include "src/objects/objects-inl.h"
 #include "src/objects/visitors.h"
+#include "src/roots/static-roots.h"
 
 namespace v8 {
 namespace internal {
@@ -68,5 +70,19 @@ Handle<HeapNumber> ReadOnlyRoots::FindHeapNumber(double value) {
   return Handle<HeapNumber>();
 }
 
+void ReadOnlyRoots::InitFromStaticRootsTable(Address cage_base) {
+  CHECK(V8_STATIC_ROOTS_BOOL);
+#if V8_STATIC_ROOTS_BOOL
+  RootIndex pos = RootIndex::kFirstReadOnlyRoot;
+  for (auto element : StaticReadOnlyRootsPointerTable) {
+    auto ptr =
+        V8HeapCompressionScheme::DecompressTaggedPointer(cage_base, element);
+    *GetLocation(pos) = ptr;
+    ++pos;
+  }
+  DCHECK_EQ(static_cast<int>(pos) - 1, RootIndex::kLastReadOnlyRoot);
+#endif  // V8_STATIC_ROOTS_BOOL
+}
+
 }  // namespace internal
 }  // namespace v8

src/roots/roots.h

@@ -643,6 +643,10 @@ class ReadOnlyRoots {
   // heap verification.
   void Iterate(RootVisitor* visitor);
 
+  // Uncompress pointers in the static roots table and store them into the
+  // actual roots table.
+  void InitFromStaticRootsTable(Address cage_base);
+
  private:
   V8_INLINE Address first_name_for_protector() const;
   V8_INLINE Address last_name_for_protector() const;

src/roots/static-roots.h

@@ -0,0 +1,20 @@
+// Copyright 2022 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_ROOTS_STATIC_ROOTS_H_
+#define V8_ROOTS_STATIC_ROOTS_H_
+
+#include "src/common/globals.h"
+#if V8_STATIC_ROOTS_BOOL
+
+namespace v8 {
+namespace internal {
+
+// TODO(olivf, v8:13466): Enable and add static roots
+constexpr static std::array<Tagged_t, 0> StaticReadOnlyRootsPointerTable = {};
+
+}  // namespace internal
+}  // namespace v8
+#endif  // V8_STATIC_ROOTS_BOOL
+#endif  // V8_ROOTS_STATIC_ROOTS_H_

src/snapshot/code-serializer.cc

@@ -108,28 +108,6 @@ AlignedCachedData* CodeSerializer::SerializeSharedFunctionInfo(
   return data.GetScriptData();
 }
 
-bool CodeSerializer::SerializeReadOnlyObject(
-    HeapObject obj, const DisallowGarbageCollection& no_gc) {
-  if (!ReadOnlyHeap::Contains(obj)) return false;
-
-  // For objects on the read-only heap, never serialize the object, but instead
-  // create a back reference that encodes the page number as the chunk_index and
-  // the offset within the page as the chunk_offset.
-  Address address = obj.address();
-  BasicMemoryChunk* chunk = BasicMemoryChunk::FromAddress(address);
-  uint32_t chunk_index = 0;
-  ReadOnlySpace* const read_only_space = isolate()->heap()->read_only_space();
-  for (ReadOnlyPage* page : read_only_space->pages()) {
-    if (chunk == page) break;
-    ++chunk_index;
-  }
-  uint32_t chunk_offset = static_cast<uint32_t>(chunk->Offset(address));
-  sink_.Put(kReadOnlyHeapRef, "ReadOnlyHeapRef");
-  sink_.PutInt(chunk_index, "ReadOnlyHeapRefChunkIndex");
-  sink_.PutInt(chunk_offset, "ReadOnlyHeapRefChunkOffset");
-  return true;
-}
-
 void CodeSerializer::SerializeObjectImpl(Handle<HeapObject> obj) {
   ReadOnlyRoots roots(isolate());
   InstanceType instance_type;
@@ -139,7 +117,7 @@ void CodeSerializer::SerializeObjectImpl(Handle<HeapObject> obj) {
     if (SerializeHotObject(raw)) return;
     if (SerializeRoot(raw)) return;
     if (SerializeBackReference(raw)) return;
-    if (SerializeReadOnlyObject(raw, no_gc)) return;
+    if (SerializeReadOnlyObjectReference(raw, &sink_)) return;
 
     instance_type = raw.map().instance_type();
     CHECK(!InstanceTypeChecker::IsCode(instance_type));

src/snapshot/code-serializer.h

@@ -111,9 +111,6 @@ class CodeSerializer : public Serializer {
  private:
   void SerializeObjectImpl(Handle<HeapObject> o) override;
 
-  bool SerializeReadOnlyObject(HeapObject obj,
-                               const DisallowGarbageCollection& no_gc);
-
   DISALLOW_GARBAGE_COLLECTION(no_gc_)
   uint32_t source_hash_;
 };

src/snapshot/deserializer.cc

@@ -911,6 +911,8 @@ int Deserializer<IsolateT>::ReadSingleBytecodeData(byte data,
     // object.
     case CASE_RANGE_ALL_SPACES(kNewObject): {
       SnapshotSpace space = NewObject::Decode(data);
+      DCHECK_IMPLIES(V8_STATIC_ROOTS_BOOL,
+                     space != SnapshotSpace::kReadOnlyHeap);
       // Save the reference type before recursing down into reading the object.
       HeapObjectReferenceType ref_type = GetAndResetNextReferenceType();
       Handle<HeapObject> heap_object = ReadObject(space);
@@ -925,9 +927,12 @@ int Deserializer<IsolateT>::ReadSingleBytecodeData(byte data,
     }
 
     // Reference an object in the read-only heap. This should be used when an
-    // object is read-only, but is not a root.
+    // object is read-only, but is not a root. Except with static roots we
+    // always use this reference to refer to read only objects since they are
+    // created by loading a memory dump of r/o space.
     case kReadOnlyHeapRef: {
-      DCHECK(isolate()->heap()->deserialization_complete());
+      DCHECK(isolate()->heap()->deserialization_complete() ||
+             V8_STATIC_ROOTS_BOOL);
       uint32_t chunk_index = source_.GetInt();
       uint32_t chunk_offset = source_.GetInt();
 
@@ -964,6 +969,7 @@ int Deserializer<IsolateT>::ReadSingleBytecodeData(byte data,
     // Find an object in the read-only object cache and write a pointer to it
     // to the current object.
     case kReadOnlyObjectCache: {
+      DCHECK(!V8_STATIC_ROOTS_BOOL);
       int cache_index = source_.GetInt();
       // TODO(leszeks): Could we use the address of the cached_read_only_object
       // entry as a Handle backing?

src/snapshot/mksnapshot.cc

@@ -18,6 +18,7 @@
 #include "src/flags/flags.h"
 #include "src/snapshot/embedded/embedded-file-writer.h"
 #include "src/snapshot/snapshot.h"
+#include "src/snapshot/static-roots-gen.h"
 
 namespace {
 
@@ -230,7 +231,7 @@ int main(int argc, char** argv) {
   std::string usage = "Usage: " + std::string(argv[0]) +
                       " [--startup-src=file]" + " [--startup-blob=file]" +
                       " [--embedded-src=file]" + " [--embedded-variant=label]" +
-                      " [--target-arch=arch]" +
+                      " [--static-roots=file]" + " [--target-arch=arch]" +
                       " [--target-os=os] [extras]\n\n";
   int result = i::FlagList::SetFlagsFromCommandLine(
       &argc, argv, true, HelpOptions(HelpOptions::kExit, usage.c_str()));
@@ -289,6 +290,10 @@ int main(int argc, char** argv) {
       // is still alive (we called DisableEmbeddedBlobRefcounting above).
       // That's fine as far as the embedded file writer is concerned.
       WriteEmbeddedFile(&embedded_writer);
+
+      if (i::v8_flags.static_roots) {
+        i::StaticRootsTableGen::write(i_isolate, i::v8_flags.static_roots);
+      }
     }
 
     if (warmup_script) {

src/snapshot/read-only-deserializer.cc

@@ -5,10 +5,12 @@
 #include "src/snapshot/read-only-deserializer.h"
 
 #include "src/api/api.h"
+#include "src/common/globals.h"
 #include "src/execution/v8threads.h"
 #include "src/heap/heap-inl.h"  // crbug.com/v8/8499
 #include "src/heap/read-only-heap.h"
 #include "src/objects/slots.h"
+#include "src/roots/static-roots.h"
 
 namespace v8 {
 namespace internal {
@@ -31,9 +33,12 @@ void ReadOnlyDeserializer::DeserializeIntoIsolate() {
 
   {
     ReadOnlyRoots roots(isolate());
-
-    roots.Iterate(this);
+    if (V8_STATIC_ROOTS_BOOL) {
+      ro_heap->read_only_space()->InitFromMemoryDump(isolate(), source());
+      roots.InitFromStaticRootsTable(isolate()->cage_base());
       ro_heap->read_only_space()->RepairFreeSpacesAfterDeserialization();
+    } else {
+      roots.Iterate(this);
 
       // Deserialize the Read-only Object Cache.
       for (;;) {
@@ -45,6 +50,8 @@ void ReadOnlyDeserializer::DeserializeIntoIsolate() {
         if (object->IsUndefined(roots)) break;
       }
       DeserializeDeferredObjects();
+    }
+
 #ifdef DEBUG
     roots.VerifyNameForProtectors();
 #endif
@@ -53,6 +60,29 @@ void ReadOnlyDeserializer::DeserializeIntoIsolate() {
 
   if (should_rehash()) {
     isolate()->heap()->InitializeHashSeed();
+    RehashReadOnly();
+  }
+}
+
+void ReadOnlyDeserializer::RehashReadOnly() {
+  DCHECK(should_rehash());
+  if (V8_STATIC_ROOTS_BOOL) {
+    // Since we are not deserializing individual objects we need to scan the
+    // heap and search for the ones that need rehashing.
+    ReadOnlyHeapObjectIterator iterator(isolate()->read_only_heap());
+    PtrComprCageBase cage_base(isolate());
+    for (HeapObject object = iterator.Next(); !object.is_null();
+         object = iterator.Next()) {
+      auto instance_type = object.map(cage_base).instance_type();
+      if (InstanceTypeChecker::IsInternalizedString(instance_type)) {
+        auto str = String::cast(object);
+        str.set_raw_hash_field(Name::kEmptyHashField);
+        str.EnsureHash();
+      } else if (object.NeedsRehashing(instance_type)) {
+        object.RehashBasedOnMap(isolate());
+      }
+    }
+  } else {
     Rehash();
   }
 }

src/snapshot/read-only-deserializer.h

@@ -22,6 +22,8 @@ class ReadOnlyDeserializer final : public Deserializer<Isolate> {
 
   // Deserialize the snapshot into an empty heap.
   void DeserializeIntoIsolate();
+
+  void RehashReadOnly();
 };
 
 }  // namespace internal

src/snapshot/read-only-serializer.cc

@@ -33,6 +33,7 @@ ReadOnlySerializer::~ReadOnlySerializer() {
 void ReadOnlySerializer::SerializeObjectImpl(Handle<HeapObject> obj) {
   CHECK(ReadOnlyHeap::Contains(*obj));
   CHECK_IMPLIES(obj->IsString(), obj->IsInternalizedString());
+  DCHECK(!V8_STATIC_ROOTS_BOOL);
 
   // There should be no references to the not_mapped_symbol except for the entry
   // in the root table, so don't try to serialize a reference and rely on the
@@ -73,14 +74,33 @@ void ReadOnlySerializer::SerializeReadOnlyRoots() {
   CHECK_IMPLIES(!allow_active_isolate_for_testing(),
                 isolate()->handle_scope_implementer()->blocks()->empty());
 
+  if (!V8_STATIC_ROOTS_BOOL) {
     ReadOnlyRoots(isolate()).Iterate(this);
-
     if (reconstruct_read_only_and_shared_object_caches_for_testing()) {
       ReconstructReadOnlyObjectCacheForTesting();
     }
+  }
 }
 
 void ReadOnlySerializer::FinalizeSerialization() {
+  if (V8_STATIC_ROOTS_BOOL) {
+    DCHECK(object_cache_empty());
+    DCHECK(deferred_objects_empty());
+    DCHECK_EQ(sink_.Position(), 0);
+
+    auto space = isolate()->read_only_heap()->read_only_space();
+    size_t num_pages = space->pages().size();
+    sink_.PutInt(num_pages, "num pages");
+    Tagged_t pos = V8HeapCompressionScheme::CompressTagged(
+        reinterpret_cast<Address>(space->pages()[0]));
+    sink_.PutInt(pos, "first page offset");
+    for (auto p : space->pages()) {
+      size_t page_size = p->area_size();
+      sink_.PutInt(page_size, "page size");
+      sink_.PutRaw(reinterpret_cast<const byte*>(p->area_start()),
+                   static_cast<int>(p->area_size()), "page");
+    }
+  } else {
     // This comes right after serialization of the other snapshots, where we
     // add entries to the read-only object cache. Add one entry with 'undefined'
     // to terminate the read-only object cache.
@@ -102,7 +122,8 @@ void ReadOnlySerializer::FinalizeSerialization() {
         CHECK_NOT_NULL(serialized_objects_.Find(object));
       }
     }
-#endif
+#endif  // DEBUG
+  }
 }
 
 bool ReadOnlySerializer::MustBeDeferred(HeapObject object) {
@@ -122,13 +143,16 @@ bool ReadOnlySerializer::SerializeUsingReadOnlyObjectCache(
     SnapshotByteSink* sink, Handle<HeapObject> obj) {
   if (!ReadOnlyHeap::Contains(*obj)) return false;
 
+  if (V8_STATIC_ROOTS_BOOL) {
+    SerializeReadOnlyObjectReference(*obj, sink);
+  } else {
     // Get the cache index and serialize it into the read-only snapshot if
     // necessary.
     int cache_index = SerializeInObjectCache(obj);
-
     // Writing out the cache entry into the calling serializer's sink.
     sink->Put(kReadOnlyObjectCache, "ReadOnlyObjectCache");
     sink->PutInt(cache_index, "read_only_object_cache_index");
+  }
 
   return true;
 }

src/snapshot/roots-serializer.h

@@ -46,6 +46,8 @@ class RootsSerializer : public Serializer {
   // Serializes |object| if not previously seen and returns its cache index.
   int SerializeInObjectCache(Handle<HeapObject> object);
 
+  bool object_cache_empty() { return object_cache_index_map_.size() == 0; }
+
  private:
   void VisitRootPointers(Root root, const char* description,
                          FullObjectSlot start, FullObjectSlot end) override;

src/snapshot/serializer.cc

@@ -1370,5 +1370,28 @@ Handle<FixedArray> ObjectCacheIndexMap::Values(Isolate* isolate) {
   return externals;
 }
 
+bool Serializer::SerializeReadOnlyObjectReference(HeapObject obj,
+                                                  SnapshotByteSink* sink) {
+  if (!ReadOnlyHeap::Contains(obj)) return false;
+
+  // For objects on the read-only heap, never serialize the object, but instead
+  // create a back reference that encodes the page number as the chunk_index and
+  // the offset within the page as the chunk_offset.
+  Address address = obj.address();
+  BasicMemoryChunk* chunk = BasicMemoryChunk::FromAddress(address);
+  uint32_t chunk_index = 0;
+  ReadOnlySpace* const read_only_space = isolate()->heap()->read_only_space();
+  DCHECK(!read_only_space->writable());
+  for (ReadOnlyPage* page : read_only_space->pages()) {
+    if (chunk == page) break;
+    ++chunk_index;
+  }
+  uint32_t chunk_offset = static_cast<uint32_t>(chunk->Offset(address));
+  sink->Put(kReadOnlyHeapRef, "ReadOnlyHeapRef");
+  sink->PutInt(chunk_index, "ReadOnlyHeapRefChunkIndex");
+  sink->PutInt(chunk_offset, "ReadOnlyHeapRefChunkOffset");
+  return true;
+}
+
 }  // namespace internal
 }  // namespace v8

src/snapshot/serializer.h

@@ -266,6 +266,8 @@ class Serializer : public SerializerDeserializer {
     return external_reference_encoder_.TryEncode(addr);
   }
 
+  bool SerializeReadOnlyObjectReference(HeapObject obj, SnapshotByteSink* sink);
+
   // GetInt reads 4 bytes at once, requiring padding at the end.
   // Use padding_offset to specify the space you want to use after padding.
   void Pad(int padding_offset = 0);
@@ -317,6 +319,8 @@ class Serializer : public SerializerDeserializer {
             Snapshot::kReconstructReadOnlyAndSharedObjectCachesForTesting) != 0;
   }
 
+  bool deferred_objects_empty() { return deferred_objects_.size() == 0; }
+
  private:
   // A circular queue of hot objects. This is added to in the same order as in
   // Deserializer::HotObjectsList, but this stores the objects as an array of

src/snapshot/static-roots-gen.cc

@@ -0,0 +1,58 @@
+// Copyright 2018 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/static-roots-gen.h"
+
+#include <fstream>
+
+#include "src/common/ptr-compr-inl.h"
+#include "src/execution/isolate.h"
+#include "src/roots/roots-inl.h"
+#include "src/roots/roots.h"
+
+namespace v8 {
+namespace internal {
+
+void StaticRootsTableGen::write(Isolate* isolate, const char* file) {
+  CHECK(file);
+  static_assert(static_cast<int>(RootIndex::kFirstReadOnlyRoot) == 0);
+
+  std::ofstream out(file);
+  const auto roots = isolate->roots_table();
+  const auto size = static_cast<int>(RootIndex::kReadOnlyRootsCount);
+
+  out << "// Copyright 2022 the V8 project authors. All rights reserved.\n"
+      << "// Use of this source code is governed by a BSD-style license "
+         "that can be\n"
+      << "// found in the LICENSE file.\n"
+      << "\n"
+      << "#ifndef V8_ROOTS_STATIC_ROOTS_H_\n"
+      << "#define V8_ROOTS_STATIC_ROOTS_H_\n"
+      << "\n"
+      << "#include \"src/common/globals.h\"\n"
+      << "#if V8_STATIC_ROOTS_BOOL\n"
+      << "\n"
+      << "namespace v8 {\n"
+      << "namespace internal {\n"
+      << "\n"
+      << "constexpr static std::array<Tagged_t, " << size
+      << "> StaticReadOnlyRootsPointerTable = {\n";
+  auto pos = RootIndex::kFirstReadOnlyRoot;
+  for (; pos <= RootIndex::kLastReadOnlyRoot; ++pos) {
+    auto el = roots[pos];
+    auto n = roots.name(pos);
+    el = V8HeapCompressionScheme::CompressTagged(el);
+    out << "    " << reinterpret_cast<void*>(el) << ",  // " << n << "\n";
+  }
+  CHECK_EQ(static_cast<int>(pos), size);
+  out << "};\n"
+      << "\n"
+      << "}  // namespace internal\n"
+      << "}  // namespace v8\n"
+      << "#endif  // V8_STATIC_ROOTS_BOOL\n"
+      << "#endif  // V8_ROOTS_STATIC_ROOTS_H_\n";
+}
+
+}  // namespace internal
+}  // namespace v8

src/snapshot/static-roots-gen.h

@@ -0,0 +1,21 @@
+// Copyright 2022 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_STATIC_ROOTS_GEN_H_
+#define V8_SNAPSHOT_STATIC_ROOTS_GEN_H_
+
+namespace v8 {
+namespace internal {
+
+class Isolate;
+
+class StaticRootsTableGen {
+ public:
+  static void write(Isolate* isolate, const char* file);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_SNAPSHOT_STATIC_ROOTS_GEN_H_

src/utils/allocation.cc

@@ -166,7 +166,7 @@ void* AllocatePages(v8::PageAllocator* page_allocator, void* hint, size_t size,
   DCHECK_NOT_NULL(page_allocator);
   DCHECK_EQ(hint, AlignedAddress(hint, alignment));
   DCHECK(IsAligned(size, page_allocator->AllocatePageSize()));
-  if (v8_flags.randomize_all_allocations) {
+  if (!hint && v8_flags.randomize_all_allocations) {
     hint = AlignedAddress(page_allocator->GetRandomMmapAddr(), alignment);
   }
   void* result = nullptr;