From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Jeremy Rose Date: Fri, 11 Mar 2022 11:17:29 -0800 Subject: be compatible with cppgc This fixes a crash that happens sporadically when Node is used in the same V8 Isolate as Blink. For example: # # Fatal error in ../../v8/src/objects/js-objects-inl.h, line 306 # Debug check failed: static_cast(index) < static_cast(GetEmbedderFieldCount()) (1 vs. 1). # # # #FailureMessage Object: 0x7ffee46fd1c0 0 Electron Framework 0x00000001181c78d9 base::debug::CollectStackTrace(void**, unsigned long) + 9 1 Electron Framework 0x00000001180ea633 base::debug::StackTrace::StackTrace() + 19 2 Electron Framework 0x000000011a04decd gin::(anonymous namespace)::PrintStackTrace() + 45 3 Electron Framework 0x0000000119a9b416 V8_Fatal(char const*, int, char const*, ...) + 326 4 Electron Framework 0x0000000119a9aeb5 v8::base::(anonymous namespace)::DefaultDcheckHandler(char const*, int, char const*) + 21 5 Electron Framework 0x000000011530763f v8::internal::JSObject::GetEmbedderFieldOffset(int) + 207 6 Electron Framework 0x00000001155f68e6 v8::internal::LocalEmbedderHeapTracer::EmbedderWriteBarrier(v8::internal::Heap*, v8::internal::JSObject) + 150 7 Electron Framework 0x00000001152cd34f v8::Object::SetAlignedPointerInInternalField(int, void*) + 639 8 Electron Framework 0x000000011d18df35 node::BaseObject::BaseObject(node::Environment*, v8::Local) + 101 9 Electron Framework 0x000000011d347b6e node::crypto::DiffieHellman::DiffieHellman(node::Environment*, v8::Local) + 14 10 Electron Framework 0x000000011d348413 node::crypto::DiffieHellman::New(v8::FunctionCallbackInfo const&) + 147 [...] This crash happens because this V8 isolate has cppgc enabled. When cppgc is enabled, V8 assumes that the first embedder field is a "type" pointer, the first 16 bits of which are the embedder ID. Node did not adhere to this requirement. Sometimes--mostly, even--this worked _by accident_. If the first field in the BaseObject was a pointer to a bit of memory that happened to contain the two-byte little-endian value 0x0001, however, V8 would take that to mean that the object was a Blink object[1], and attempt to read the pointer in the second embedder slot, which would result in a CHECK. This change adds an "embedder id" pointer as the first embedder field in all Node-managed objects. This ensures that cppgc will always skip over Node objects. This patch should be upstreamed to Node. [1]: https://source.chromium.org/chromium/chromium/src/+/main:gin/public/gin_embedders.h;l=20;drc=5a758a97032f0b656c3c36a3497560762495501a See also: https://source.chromium.org/chromium/chromium/src/+/main:v8/include/v8-cppgc.h;l=70-76;drc=5a758a97032f0b656c3c36a3497560762495501a diff --git a/src/base_object-inl.h b/src/base_object-inl.h index bb1e8d4b46bce3bf08f730ac5d43f7113d17ae39..6da0669943fc6465ffc47a1c8c3dadfea6beb1c9 100644 --- a/src/base_object-inl.h +++ b/src/base_object-inl.h @@ -32,10 +32,21 @@ namespace node { +namespace { +// This just has to be different from the Chromium ones: +// https://source.chromium.org/chromium/chromium/src/+/main:gin/public/gin_embedders.h;l=18-23;drc=5a758a97032f0b656c3c36a3497560762495501a +// Otherwise, when Node is loaded in an isolate which uses cppgc, cppgc will +// misinterpret the data stored in the embedder fields and try to garbage +// collect them. +static uint16_t kNodeEmbedderId = 0x90de; +} + BaseObject::BaseObject(Environment* env, v8::Local object) : persistent_handle_(env->isolate(), object), env_(env) { CHECK_EQ(false, object.IsEmpty()); - CHECK_GT(object->InternalFieldCount(), 0); + CHECK_GT(object->InternalFieldCount(), BaseObject::kSlot); + object->SetAlignedPointerInInternalField(BaseObject::kWrapperType, + &kNodeEmbedderId); object->SetAlignedPointerInInternalField( BaseObject::kSlot, static_cast(this)); @@ -151,7 +162,8 @@ bool BaseObject::IsWeakOrDetached() const { void BaseObject::LazilyInitializedJSTemplateConstructor( const v8::FunctionCallbackInfo& args) { DCHECK(args.IsConstructCall()); - DCHECK_GT(args.This()->InternalFieldCount(), 0); + DCHECK_GT(args.This()->InternalFieldCount(), BaseObject::kSlot); + args.This()->SetAlignedPointerInInternalField(BaseObject::kWrapperType, &kNodeEmbedderId); args.This()->SetAlignedPointerInInternalField(BaseObject::kSlot, nullptr); } diff --git a/src/base_object.h b/src/base_object.h index d46a0f216009c63f45c440fc352b54d1ac4a08d8..81913c0d7762bf499ee19aaa3b63b986ca370bb4 100644 --- a/src/base_object.h +++ b/src/base_object.h @@ -40,7 +40,7 @@ class TransferData; class BaseObject : public MemoryRetainer { public: - enum InternalFields { kSlot, kInternalFieldCount }; + enum InternalFields { kWrapperType, kSlot, kInternalFieldCount }; // Associates this object with `object`. It uses the 0th internal field for // that, and in particular aborts if there is no such field.