src: tag v8 aligned pointer slots with embedder data type tags

legendecas · web-flow · commit b8e264d3c36d · 2025-11-08T14:27:25.000Z
PR-URL: #60602 Fixes: #60589 Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
diff --git a/src/README.md b/src/README.md
@@ -126,10 +126,10 @@ Typical ways of working with internal fields are:
 * `obj->GetInternalField(i)` to get a JavaScript value from an internal field.
 * `obj->SetInternalField(i, v)` to store a JavaScript value in an
   internal field.
-* `obj->GetAlignedPointerFromInternalField(i)` to get a `void*` pointer from an
-  internal field.
-* `obj->SetAlignedPointerInInternalField(i, p)` to store a `void*` pointer in an
-  internal field.
+* `obj->GetAlignedPointerFromInternalField(i, EmbedderDataTag::kDefault)` to get
+  a `void*` pointer from an internal field.
+* `obj->SetAlignedPointerInInternalField(i, p, EmbedderDataTag::kDefault)` to store
+  a `void*` pointer in an internal field.
 
 [`Context`][]s provide the same feature under the name “embedder data”.
 
diff --git a/src/base_object-inl.h b/src/base_object-inl.h
@@ -74,30 +74,34 @@ bool BaseObject::IsBaseObject(IsolateData* isolate_data,
     return false;
   }
 
-  uint16_t* ptr = static_cast<uint16_t*>(
-      obj->GetAlignedPointerFromInternalField(BaseObject::kEmbedderType));
+  uint16_t* ptr =
+      static_cast<uint16_t*>(obj->GetAlignedPointerFromInternalField(
+          BaseObject::kEmbedderType, EmbedderDataTag::kEmbedderType));
   return ptr == isolate_data->embedder_id_for_non_cppgc();
 }
 
 void BaseObject::TagBaseObject(IsolateData* isolate_data,
                                v8::Local<v8::Object> object) {
   DCHECK_GE(object->InternalFieldCount(), BaseObject::kInternalFieldCount);
   object->SetAlignedPointerInInternalField(
-      BaseObject::kEmbedderType, isolate_data->embedder_id_for_non_cppgc());
+      BaseObject::kEmbedderType,
+      isolate_data->embedder_id_for_non_cppgc(),
+      EmbedderDataTag::kEmbedderType);
 }
 
 void BaseObject::SetInternalFields(IsolateData* isolate_data,
                                    v8::Local<v8::Object> object,
                                    void* slot) {
   TagBaseObject(isolate_data, object);
-  object->SetAlignedPointerInInternalField(BaseObject::kSlot, slot);
+  object->SetAlignedPointerInInternalField(
+      BaseObject::kSlot, slot, EmbedderDataTag::kDefault);
 }
 
 BaseObject* BaseObject::FromJSObject(v8::Local<v8::Value> value) {
   v8::Local<v8::Object> obj = value.As<v8::Object>();
   DCHECK_GE(obj->InternalFieldCount(), BaseObject::kInternalFieldCount);
-  return static_cast<BaseObject*>(
-      obj->GetAlignedPointerFromInternalField(BaseObject::kSlot));
+  return static_cast<BaseObject*>(obj->GetAlignedPointerFromInternalField(
+      BaseObject::kSlot, EmbedderDataTag::kDefault));
 }
 
 template <typename T>
diff --git a/src/base_object.cc b/src/base_object.cc
@@ -45,7 +45,8 @@ BaseObject::~BaseObject() {
 
   {
     HandleScope handle_scope(realm()->isolate());
-    object()->SetAlignedPointerInInternalField(BaseObject::kSlot, nullptr);
+    object()->SetAlignedPointerInInternalField(
+        BaseObject::kSlot, nullptr, EmbedderDataTag::kDefault);
   }
 }
 
diff --git a/src/base_object.h b/src/base_object.h
@@ -27,6 +27,7 @@
 #include <type_traits>  // std::remove_reference
 #include "base_object_types.h"
 #include "memory_tracker.h"
+#include "node_v8_embedder.h"
 #include "util.h"
 #include "v8.h"
 
diff --git a/src/cppgc_helpers-inl.h b/src/cppgc_helpers-inl.h
@@ -19,8 +19,10 @@ void CppgcMixin::Wrap(T* ptr, Realm* realm, v8::Local<v8::Object> obj) {
   v8::Object::Wrap<v8::CppHeapPointerTag::kDefaultTag>(isolate, obj, wrappable);
   // Keep the layout consistent with BaseObjects.
   obj->SetAlignedPointerInInternalField(
-      kEmbedderType, realm->isolate_data()->embedder_id_for_cppgc());
-  obj->SetAlignedPointerInInternalField(kSlot, ptr);
+      kEmbedderType,
+      realm->isolate_data()->embedder_id_for_cppgc(),
+      EmbedderDataTag::kEmbedderType);
+  obj->SetAlignedPointerInInternalField(kSlot, ptr, EmbedderDataTag::kDefault);
   realm->TrackCppgcWrapper(ptr);
 }
 
@@ -41,7 +43,8 @@ T* CppgcMixin::Unwrap(v8::Local<v8::Object> obj) {
   if (obj->InternalFieldCount() != T::kInternalFieldCount) {
     return nullptr;
   }
-  T* ptr = static_cast<T*>(obj->GetAlignedPointerFromInternalField(T::kSlot));
+  T* ptr = static_cast<T*>(obj->GetAlignedPointerFromInternalField(
+      T::kSlot, EmbedderDataTag::kDefault));
   return ptr;
 }
 
diff --git a/src/env-inl.h b/src/env-inl.h
@@ -196,9 +196,8 @@ inline Environment* Environment::GetCurrent(v8::Local<v8::Context> context) {
   if (!ContextEmbedderTag::IsNodeContext(context)) [[unlikely]] {
     return nullptr;
   }
-  return static_cast<Environment*>(
-      context->GetAlignedPointerFromEmbedderData(
-          ContextEmbedderIndex::kEnvironment));
+  return static_cast<Environment*>(context->GetAlignedPointerFromEmbedderData(
+      ContextEmbedderIndex::kEnvironment, EmbedderDataTag::kPerContextData));
 }
 
 inline Environment* Environment::GetCurrent(
diff --git a/src/env.cc b/src/env.cc
@@ -674,12 +674,16 @@ void Environment::AssignToContext(Local<v8::Context> context,
                                   Realm* realm,
                                   const ContextInfo& info) {
   context->SetAlignedPointerInEmbedderData(ContextEmbedderIndex::kEnvironment,
-                                           this);
-  context->SetAlignedPointerInEmbedderData(ContextEmbedderIndex::kRealm, realm);
+                                           this,
+                                           EmbedderDataTag::kPerContextData);
+  context->SetAlignedPointerInEmbedderData(
+      ContextEmbedderIndex::kRealm, realm, EmbedderDataTag::kPerContextData);
 
   // ContextifyContexts will update this to a pointer to the native object.
   context->SetAlignedPointerInEmbedderData(
-      ContextEmbedderIndex::kContextifyContext, nullptr);
+      ContextEmbedderIndex::kContextifyContext,
+      nullptr,
+      EmbedderDataTag::kPerContextData);
 
   // This must not be done before other context fields are initialized.
   ContextEmbedderTag::TagNodeContext(context);
@@ -695,11 +699,15 @@ void Environment::AssignToContext(Local<v8::Context> context,
 void Environment::UnassignFromContext(Local<v8::Context> context) {
   if (!context.IsEmpty()) {
     context->SetAlignedPointerInEmbedderData(ContextEmbedderIndex::kEnvironment,
-                                             nullptr);
+                                             nullptr,
+                                             EmbedderDataTag::kPerContextData);
     context->SetAlignedPointerInEmbedderData(ContextEmbedderIndex::kRealm,
-                                             nullptr);
+                                             nullptr,
+                                             EmbedderDataTag::kPerContextData);
     context->SetAlignedPointerInEmbedderData(
-        ContextEmbedderIndex::kContextifyContext, nullptr);
+        ContextEmbedderIndex::kContextifyContext,
+        nullptr,
+        EmbedderDataTag::kPerContextData);
   }
   UntrackContext(context);
 }
diff --git a/src/histogram.cc b/src/histogram.cc
@@ -136,7 +136,8 @@ HistogramBase::HistogramBase(
   MakeWeak();
   wrap->SetAlignedPointerInInternalField(
       HistogramImpl::InternalFields::kImplField,
-      static_cast<HistogramImpl*>(this));
+      static_cast<HistogramImpl*>(this),
+      EmbedderDataTag::kDefault);
 }
 
 HistogramBase::HistogramBase(
@@ -148,7 +149,8 @@ HistogramBase::HistogramBase(
   MakeWeak();
   wrap->SetAlignedPointerInInternalField(
       HistogramImpl::InternalFields::kImplField,
-      static_cast<HistogramImpl*>(this));
+      static_cast<HistogramImpl*>(this),
+      EmbedderDataTag::kDefault);
 }
 
 void HistogramBase::MemoryInfo(MemoryTracker* tracker) const {
@@ -362,7 +364,8 @@ IntervalHistogram::IntervalHistogram(
   MakeWeak();
   wrap->SetAlignedPointerInInternalField(
       HistogramImpl::InternalFields::kImplField,
-      static_cast<HistogramImpl*>(this));
+      static_cast<HistogramImpl*>(this),
+      EmbedderDataTag::kDefault);
   uv_timer_init(env->event_loop(), &timer_);
 }
 
@@ -600,8 +603,8 @@ double HistogramImpl::FastGetPercentile(Local<Value> receiver,
 HistogramImpl* HistogramImpl::FromJSObject(Local<Value> value) {
   auto obj = value.As<Object>();
   DCHECK_GE(obj->InternalFieldCount(), HistogramImpl::kInternalFieldCount);
-  return static_cast<HistogramImpl*>(
-      obj->GetAlignedPointerFromInternalField(HistogramImpl::kImplField));
+  return static_cast<HistogramImpl*>(obj->GetAlignedPointerFromInternalField(
+      HistogramImpl::kImplField, EmbedderDataTag::kDefault));
 }
 
 std::unique_ptr<worker::TransferData>
diff --git a/src/js_udp_wrap.cc b/src/js_udp_wrap.cc
@@ -55,8 +55,9 @@ JSUDPWrap::JSUDPWrap(Environment* env, Local<Object> obj)
   : AsyncWrap(env, obj, PROVIDER_JSUDPWRAP) {
   MakeWeak();
 
-  obj->SetAlignedPointerInInternalField(
-      kUDPWrapBaseField, static_cast<UDPWrapBase*>(this));
+  obj->SetAlignedPointerInInternalField(kUDPWrapBaseField,
+                                        static_cast<UDPWrapBase*>(this),
+                                        EmbedderDataTag::kDefault);
 }
 
 int JSUDPWrap::RecvStart() {
diff --git a/src/node_context_data.h b/src/node_context_data.h
@@ -3,6 +3,7 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+#include "node_v8_embedder.h"
 #include "util.h"
 #include "v8.h"
 
@@ -135,7 +136,8 @@ class ContextEmbedderTag {
     // context.
     context->SetAlignedPointerInEmbedderData(
         ContextEmbedderIndex::kContextTag,
-        ContextEmbedderTag::kNodeContextTagPtr);
+        ContextEmbedderTag::kNodeContextTagPtr,
+        EmbedderDataTag::kPerContextData);
   }
 
   static inline bool IsNodeContext(v8::Local<v8::Context> context) {
@@ -147,7 +149,8 @@ class ContextEmbedderTag {
       return false;
     }
     if (context->GetAlignedPointerFromEmbedderData(
-            ContextEmbedderIndex::kContextTag) !=
+            ContextEmbedderIndex::kContextTag,
+            EmbedderDataTag::kPerContextData) !=
         ContextEmbedderTag::kNodeContextTagPtr) [[unlikely]] {
       return false;
     }
diff --git a/src/node_contextify.cc b/src/node_contextify.cc
@@ -164,9 +164,12 @@ ContextifyContext::ContextifyContext(Environment* env,
   // This should only be done after the initial initializations of the context
   // global object is finished.
   DCHECK_NULL(v8_context->GetAlignedPointerFromEmbedderData(
-      ContextEmbedderIndex::kContextifyContext));
+      ContextEmbedderIndex::kContextifyContext,
+      EmbedderDataTag::kPerContextData));
   v8_context->SetAlignedPointerInEmbedderData(
-      ContextEmbedderIndex::kContextifyContext, this);
+      ContextEmbedderIndex::kContextifyContext,
+      this,
+      EmbedderDataTag::kPerContextData);
 }
 
 void ContextifyContext::InitializeGlobalTemplates(IsolateData* isolate_data) {
@@ -473,7 +476,8 @@ ContextifyContext* ContextifyContext::Get(Local<Object> object) {
   }
   return static_cast<ContextifyContext*>(
       context->GetAlignedPointerFromEmbedderData(
-          ContextEmbedderIndex::kContextifyContext));
+          ContextEmbedderIndex::kContextifyContext,
+          EmbedderDataTag::kPerContextData));
 }
 
 bool ContextifyContext::IsStillInitializing(const ContextifyContext* ctx) {
diff --git a/src/node_object_wrap.h b/src/node_object_wrap.h
@@ -49,7 +49,8 @@ class ObjectWrap {
     assert(handle->InternalFieldCount() > 0);
     // Cast to ObjectWrap before casting to T.  A direct cast from void
     // to T won't work right when T has more than one base class.
-    void* ptr = handle->GetAlignedPointerFromInternalField(0);
+    void* ptr = handle->GetAlignedPointerFromInternalField(
+        0, v8::kEmbedderDataTypeTagDefault);
     ObjectWrap* wrap = static_cast<ObjectWrap*>(ptr);
     return static_cast<T*>(wrap);
   }
@@ -75,7 +76,8 @@ class ObjectWrap {
   inline void Wrap(v8::Local<v8::Object> handle) {
     assert(persistent().IsEmpty());
     assert(handle->InternalFieldCount() > 0);
-    handle->SetAlignedPointerInInternalField(0, this);
+    handle->SetAlignedPointerInInternalField(
+        0, this, v8::kEmbedderDataTypeTagDefault);
     persistent().Reset(v8::Isolate::GetCurrent(), handle);
     MakeWeak();
   }
diff --git a/src/node_process_methods.cc b/src/node_process_methods.cc
@@ -673,7 +673,8 @@ void BindingData::RegisterExternalReferences(
 BindingData* BindingData::FromV8Value(Local<Value> value) {
   Local<Object> v8_object = value.As<Object>();
   return static_cast<BindingData*>(
-      v8_object->GetAlignedPointerFromInternalField(BaseObject::kSlot));
+      v8_object->GetAlignedPointerFromInternalField(BaseObject::kSlot,
+                                                    EmbedderDataTag::kDefault));
 }
 
 void BindingData::MemoryInfo(MemoryTracker* tracker) const {
diff --git a/src/node_realm-inl.h b/src/node_realm-inl.h
@@ -20,8 +20,8 @@ inline Realm* Realm::GetCurrent(v8::Local<v8::Context> context) {
   if (!ContextEmbedderTag::IsNodeContext(context)) [[unlikely]] {
     return nullptr;
   }
-  return static_cast<Realm*>(
-      context->GetAlignedPointerFromEmbedderData(ContextEmbedderIndex::kRealm));
+  return static_cast<Realm*>(context->GetAlignedPointerFromEmbedderData(
+      ContextEmbedderIndex::kRealm, EmbedderDataTag::kPerContextData));
 }
 
 inline Realm* Realm::GetCurrent(
diff --git a/src/node_snapshotable.cc b/src/node_snapshotable.cc
@@ -1309,7 +1309,8 @@ StartupData SerializeNodeContextData(Local<Context> holder,
     case ContextEmbedderIndex::kContextifyContext:
     case ContextEmbedderIndex::kRealm:
     case ContextEmbedderIndex::kContextTag: {
-      void* data = holder->GetAlignedPointerFromEmbedderData(index);
+      void* data = holder->GetAlignedPointerFromEmbedderData(
+          index, EmbedderDataTag::kPerContextData);
       per_process::Debug(
           DebugCategory::MKSNAPSHOT,
           "Serialize context data, index=%d, holder=%p, ptr=%p\n",
@@ -1400,7 +1401,8 @@ StartupData SerializeNodeContextInternalFields(Local<Object> holder,
   // For the moment we do not set any internal fields in ArrayBuffer
   // or ArrayBufferViews, so just return nullptr.
   if (holder->IsArrayBuffer() || holder->IsArrayBufferView()) {
-    CHECK_NULL(holder->GetAlignedPointerFromInternalField(index));
+    CHECK_NULL(holder->GetAlignedPointerFromInternalField(
+        index, EmbedderDataTag::kDefault));
     return StartupData{nullptr, 0};
   }
 
@@ -1419,8 +1421,9 @@ StartupData SerializeNodeContextInternalFields(Local<Object> holder,
                      static_cast<int>(index),
                      *holder);
 
-  BaseObject* object_ptr = static_cast<BaseObject*>(
-      holder->GetAlignedPointerFromInternalField(BaseObject::kSlot));
+  BaseObject* object_ptr =
+      static_cast<BaseObject*>(holder->GetAlignedPointerFromInternalField(
+          BaseObject::kSlot, EmbedderDataTag::kDefault));
   // If the native object is already set to null, ignore it.
   if (object_ptr == nullptr) {
     return StartupData{nullptr, 0};
diff --git a/src/node_v8_embedder.h b/src/node_v8_embedder.h
@@ -0,0 +1,26 @@
+#ifndef SRC_NODE_V8_EMBEDDER_H_
+#define SRC_NODE_V8_EMBEDDER_H_
+
+#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
+
+#include <cstdint>
+
+namespace node {
+
+// Type tags for different kinds of embedder data stored in V8 aligned pointer
+// slots.
+enum EmbedderDataTag : uint16_t {
+  // kDefault is used in slots that don't use V8 type tagging.
+  kDefault = 0,
+  // kEmbedderType is used by BaseObject to store the kEmbedderType value.
+  kEmbedderType,
+  // kPerContextData is used to store data on a `v8::Context`, including
+  // slots indexed by ContextEmbedderIndex.
+  kPerContextData,
+};
+
+}  // namespace node
+
+#endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
+
+#endif  // SRC_NODE_V8_EMBEDDER_H_
diff --git a/src/stream_base-inl.h b/src/stream_base-inl.h
diff --git a/src/udp_wrap.cc b/src/udp_wrap.cc

Original file line number	Diff line number	Diff line change
`@@ -45,7 +45,8 @@ BaseObject::~BaseObject() {`
`45`	`45`
`46`	`46`	`{`
`47`	`47`	`HandleScope handle_scope(realm()->isolate());`
`48`		`- object()->SetAlignedPointerInInternalField(BaseObject::kSlot, nullptr);`
	`48`	`+ object()->SetAlignedPointerInInternalField(`
	`49`	`+ BaseObject::kSlot, nullptr, EmbedderDataTag::kDefault);`
`49`	`50`	`}`
`50`	`51`	`}`
`51`	`52`
Original file line number	Diff line number	Diff line change
`@@ -196,9 +196,8 @@ inline Environment* Environment::GetCurrent(v8::Local<v8::Context> context) {`
`196`	`196`	`if (!ContextEmbedderTag::IsNodeContext(context)) [[unlikely]] {`
`197`	`197`	`return nullptr;`
`198`	`198`	`}`
`199`		`- return static_cast<Environment*>(`
`200`		`- context->GetAlignedPointerFromEmbedderData(`
`201`		`- ContextEmbedderIndex::kEnvironment));`
	`199`	`+ return static_cast<Environment*>(context->GetAlignedPointerFromEmbedderData(`
	`200`	`+ ContextEmbedderIndex::kEnvironment, EmbedderDataTag::kPerContextData));`
`202`	`201`	`}`
`203`	`202`
`204`	`203`	`inline Environment* Environment::GetCurrent(`