[snapshot] Support shared string table with --stress-snapshot

Bug: v8:12584, v8:12007
Change-Id: Iac3c8b1c5935142742dddc7e12293fd7640c06a3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3419736
Auto-Submit: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78804}

src/snapshot/read-only-serializer.cc

@@ -74,7 +74,7 @@ void ReadOnlySerializer::SerializeReadOnlyRoots() {
 
   ReadOnlyRoots(isolate()).Iterate(this);
 
-  if (reconstruct_read_only_object_cache_for_testing()) {
+  if (reconstruct_read_only_and_shared_object_caches_for_testing()) {
     ReconstructReadOnlyObjectCacheForTesting();
   }
 }

src/snapshot/serializer.h

@@ -309,8 +309,9 @@ class Serializer : public SerializerDeserializer {
     return (flags_ & Snapshot::kAllowActiveIsolateForTesting) != 0;
   }
 
-  bool reconstruct_read_only_object_cache_for_testing() const {
-    return (flags_ & Snapshot::kReconstructReadOnlyObjectCacheForTesting) != 0;
+  bool reconstruct_read_only_and_shared_object_caches_for_testing() const {
+    return (flags_ &
+            Snapshot::kReconstructReadOnlyAndSharedObjectCachesForTesting) != 0;
   }
 
  private:

src/snapshot/shared-heap-serializer.cc

@@ -65,10 +65,6 @@ void SharedHeapSerializer::FinalizeSerialization() {
   Pad();
 
 #ifdef DEBUG
-  // During snapshotting there is no shared heap.
-  CHECK(!isolate()->is_shared());
-  CHECK_NULL(isolate()->shared_isolate());
-
   // Check that all serialized object are in shared heap and not RO. RO objects
   // should be in the RO snapshot.
   IdentityMap<int, base::DefaultAllocationPolicy>::IteratableScope it_scope(
@@ -90,6 +86,20 @@ bool SharedHeapSerializer::SerializeUsingSharedHeapObjectCache(
     SnapshotByteSink* sink, Handle<HeapObject> obj) {
   if (!ShouldBeInSharedHeapObjectCache(*obj)) return false;
   int cache_index = SerializeInObjectCache(obj);
+
+  // When testing deserialization of a snapshot from a live isolate, the shared
+  // object cache needs to be extended because the live isolate may have had new
+  // internalized strings that were not present in the startup snapshot to be
+  // serialized.
+  if (reconstruct_read_only_and_shared_object_caches_for_testing()) {
+    const size_t existing_cache_size =
+        isolate()->shared_heap_object_cache()->size();
+    DCHECK_LE(base::checked_cast<size_t>(cache_index), existing_cache_size);
+    if (base::checked_cast<size_t>(cache_index) == existing_cache_size) {
+      isolate()->shared_heap_object_cache()->push_back(*obj);
+    }
+  }
+
   sink->Put(kSharedHeapObjectCache, "SharedHeapObjectCache");
   sink->PutInt(cache_index, "shared_heap_object_cache_index");
   return true;
@@ -170,5 +180,18 @@ void SharedHeapSerializer::SerializeObjectImpl(Handle<HeapObject> obj) {
 #endif
 }
 
+void SharedHeapSerializer::
+    ReconstructSharedHeapObjectCacheForTestingIfNeeded() {
+  if (!reconstruct_read_only_and_shared_object_caches_for_testing()) return;
+  std::vector<Object>* cache = isolate()->shared_heap_object_cache();
+  DCHECK_EQ(isolate()->shared_isolate()->shared_heap_object_cache(), cache);
+  for (size_t i = 0, size = cache->size(); i < size; i++) {
+    Handle<HeapObject> obj(HeapObject::cast(cache->at(i)), isolate());
+    int cache_index = SerializeInObjectCache(obj);
+    USE(cache_index);
+    DCHECK_EQ(cache_index, i);
+  }
+}
+
 }  // namespace internal
 }  // namespace v8

src/snapshot/shared-heap-serializer.h

@@ -43,6 +43,8 @@ class V8_EXPORT_PRIVATE SharedHeapSerializer : public RootsSerializer {
   bool SerializeUsingSharedHeapObjectCache(SnapshotByteSink* sink,
                                            Handle<HeapObject> obj);
 
+  void ReconstructSharedHeapObjectCacheForTestingIfNeeded();
+
   static bool CanBeInSharedOldSpace(HeapObject obj);
 
   static bool ShouldBeInSharedHeapObjectCache(HeapObject obj);

src/snapshot/snapshot.cc

@@ -313,13 +313,17 @@ void Snapshot::SerializeDeserializeAndVerifyForTesting(
   // Test serialization.
   {
     GlobalSafepointScope global_safepoint(isolate);
+    base::Optional<SafepointScope> shared_isolate_safepoint_scope;
+    if (Isolate* shared_isolate = isolate->shared_isolate()) {
+      shared_isolate_safepoint_scope.emplace(shared_isolate->heap());
+    }
     DisallowGarbageCollection no_gc;
 
     Snapshot::SerializerFlags flags(
         Snapshot::kAllowUnknownExternalReferencesForTesting |
         Snapshot::kAllowActiveIsolateForTesting |
-        (ReadOnlyHeap::IsReadOnlySpaceShared()
-             ? Snapshot::kReconstructReadOnlyObjectCacheForTesting
+        ((isolate->shared_isolate() || ReadOnlyHeap::IsReadOnlySpaceShared())
+             ? Snapshot::kReconstructReadOnlyAndSharedObjectCachesForTesting
              : 0));
     serialized_data = Snapshot::Create(isolate, *default_context,
                                        global_safepoint, no_gc, flags);
@@ -337,6 +341,9 @@ void Snapshot::SerializeDeserializeAndVerifyForTesting(
     new_isolate->set_snapshot_blob(&serialized_data);
     new_isolate->set_array_buffer_allocator(
         v8::ArrayBuffer::Allocator::NewDefaultAllocator());
+    if (Isolate* shared_isolate = isolate->shared_isolate()) {
+      new_isolate->set_shared_isolate(shared_isolate);
+    }
     CHECK(Snapshot::Initialize(new_isolate));
 
     HandleScope scope(new_isolate);
@@ -376,6 +383,7 @@ v8::StartupData Snapshot::Create(
 
   SharedHeapSerializer shared_heap_serializer(isolate, flags,
                                               &read_only_serializer);
+  shared_heap_serializer.ReconstructSharedHeapObjectCacheForTestingIfNeeded();
 
   StartupSerializer startup_serializer(isolate, flags, &read_only_serializer,
                                        &shared_heap_serializer);

src/snapshot/snapshot.h

@@ -39,15 +39,17 @@ class Snapshot : public AllStatic {
     // after deserialization.
     // If unset, we assert that these previously mentioned areas are empty.
     kAllowActiveIsolateForTesting = 1 << 1,
-    // If set, the ReadOnlySerializer reconstructs the read-only object cache
-    // from the existing ReadOnlyHeap's read-only object cache so the same
+    // 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. 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.
-    kReconstructReadOnlyObjectCacheForTesting = 1 << 2,
+    // 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 =