[v8.x backport] node internals' postmortem metadata (#14901, #18530, #18653)

doc/guides/node-postmortem-support.md

@@ -0,0 +1,72 @@
+# Postmortem Support
+
+Postmortem metadata are constants present in the final build which can be used
+by debuggers and other tools to navigate through internal structures of software
+when analyzing its memory (either on a running process or a core dump). Node
+provides this metadata in its builds for V8 and Node internal structures.
+
+
+### V8 Postmortem metadata
+
+V8 prefixes all postmortem constants with `v8dbg_`, and they allow inspection of
+objects on the heap as well as object properties and references. V8 generates
+those symbols with a script (`deps/v8/tools/gen-postmortem-metadata.py`), and
+Node always includes these constants in the final build.
+
+### Node Debug Symbols
+
+Node prefixes all postmortem constants with `nodedbg_`, and they complement V8
+constants by providing ways to inspect Node-specific structures, like
+`node::Environment`, `node::BaseObject` and its descendants, classes from
+`src/utils.h` and others. Those constants are declared in
+`src/node_postmortem_metadata.cc`, and most of them are calculated at compile
+time.
+
+#### Calculating offset of class members
+
+Node constants referring to the offset of class members in memory are calculated
+at compile time. Because of that, those class members must be at a fixed offset
+from the start of the class. That's not a problem in most cases, but it also
+means that those members should always come after any templated member on the
+class definition.
+
+For example, if we want to add a constant with the offset for
+`ReqWrap::req_wrap_queue_`, it should be defined after `ReqWrap::req_`, because
+`sizeof(req_)` depends on the type of T, which means the class definition should
+be like this:
+
+```c++
+template <typename T>
+class ReqWrap : public AsyncWrap {
+ private:
+  // req_wrap_queue_ comes before any templated member, which places it in a
+  // fixed offset from the start of the class
+  ListNode<ReqWrap> req_wrap_queue_;
+
+  T req_;
+};
+```
+
+instead of:
+
+```c++
+template <typename T>
+class ReqWrap : public AsyncWrap {
+ private:
+  T req_;
+
+  // req_wrap_queue_ comes after a templated member, which means it won't be in
+  // a fixed offset from the start of the class
+  ListNode<ReqWrap> req_wrap_queue_;
+};
+```
+
+There are also tests on `test/cctest/test_node_postmortem_metadata.cc` to make
+sure all Node postmortem metadata are calculated correctly.
+
+## Tools and References
+
+* [llnode](https://github.com/nodejs/llnode): LLDB plugin
+* [`mdb_v8`](https://github.com/joyent/mdb_v8): mdb plugin
+* [nodejs/post-mortem](https://github.com/nodejs/post-mortem): Node.js
+post-mortem working group

node.gyp

@@ -203,6 +203,7 @@
         'src/node_os.cc',
         'src/node_platform.cc',
         'src/node_perf.cc',
+        'src/node_postmortem_metadata.cc',
         'src/node_serdes.cc',
         'src/node_trace_events.cc',
         'src/node_url.cc',
@@ -815,6 +816,7 @@
         'test/cctest/node_test_fixture.cc',
         'test/cctest/test_aliased_buffer.cc',
         'test/cctest/test_base64.cc',
+        'test/cctest/test_node_postmortem_metadata.cc',
         'test/cctest/test_environment.cc',
         'test/cctest/test_util.cc',
         'test/cctest/test_url.cc'
@@ -828,6 +830,7 @@
         ['node_target_type!="static_library"', {
           'libraries': [
             '<(OBJ_PATH)<(OBJ_SEPARATOR)async_wrap.<(OBJ_SUFFIX)',
+            '<(OBJ_PATH)<(OBJ_SEPARATOR)handle_wrap.<(OBJ_SUFFIX)',
             '<(OBJ_PATH)<(OBJ_SEPARATOR)env.<(OBJ_SUFFIX)',
             '<(OBJ_PATH)<(OBJ_SEPARATOR)node.<(OBJ_SUFFIX)',
             '<(OBJ_PATH)<(OBJ_SEPARATOR)node_buffer.<(OBJ_SUFFIX)',

src/base-object.h

@@ -65,6 +65,12 @@ class BaseObject {
   static inline void WeakCallback(
       const v8::WeakCallbackInfo<Type>& data);
 
+  // persistent_handle_ needs to be at a fixed offset from the start of the
+  // class because it is used by src/node_postmortem_metadata.cc to calculate
+  // offsets and generate debug symbols for BaseObject, which assumes that the
+  // position of members in memory are predictable. For more information please
+  // refer to `doc/guides/node-postmortem-support.md`
+  friend int GenDebugSymbols();
   v8::Persistent<v8::Object> persistent_handle_;
   Environment* env_;
 };

src/env.h

@@ -724,6 +724,13 @@ class Environment {
   std::unique_ptr<inspector::Agent> inspector_agent_;
 #endif
 
+  // handle_wrap_queue_ and req_wrap_queue_ needs to be at a fixed offset from
+  // the start of the class because it is used by
+  // src/node_postmortem_metadata.cc to calculate offsets and generate debug
+  // symbols for Environment, which assumes that the position of members in
+  // memory are predictable. For more information please refer to
+  // `doc/guides/node-postmortem-support.md`
+  friend int GenDebugSymbols();
   HandleWrapQueue handle_wrap_queue_;
   ReqWrapQueue req_wrap_queue_;
   ListHead<HandleCleanup,

src/handle_wrap.h

@@ -81,6 +81,13 @@ class HandleWrap : public AsyncWrap {
   friend class Environment;
   friend void GetActiveHandles(const v8::FunctionCallbackInfo<v8::Value>&);
   static void OnClose(uv_handle_t* handle);
+
+  // handle_wrap_queue_ needs to be at a fixed offset from the start of the
+  // class because it is used by src/node_postmortem_metadata.cc to calculate
+  // offsets and generate debug symbols for HandleWrap, which assumes that the
+  // position of members in memory are predictable. For more information please
+  // refer to `doc/guides/node-postmortem-support.md`
+  friend int GenDebugSymbols();
   ListNode<HandleWrap> handle_wrap_queue_;
   enum { kInitialized, kClosing, kClosingWithCallback, kClosed } state_;
   uv_handle_t* const handle_;

src/node_postmortem_metadata.cc

@@ -0,0 +1,64 @@
+#include "env.h"
+#include "base-object-inl.h"
+#include "handle_wrap.h"
+#include "util-inl.h"
+#include "req-wrap.h"
+#include "v8abbr.h"
+
+#define NODEDBG_SYMBOL(Name)  nodedbg_ ## Name
+
+// nodedbg_offset_CLASS__MEMBER__TYPE: Describes the offset to a class member.
+#define NODEDBG_OFFSET(Class, Member, Type) \
+    NODEDBG_SYMBOL(offset_ ## Class ## __ ## Member ## __ ## Type)
+
+// These are the constants describing Node internal structures. Every constant
+// should use the format described above.  These constants are declared as
+// global integers so that they'll be present in the generated node binary. They
+// also need to be declared outside any namespace to avoid C++ name-mangling.
+#define NODE_OFFSET_POSTMORTEM_METADATA(V)                                    \
+  V(BaseObject, persistent_handle_, v8_Persistent_v8_Object,                  \
+    BaseObject::persistent_handle_)                                           \
+  V(Environment, handle_wrap_queue_, Environment_HandleWrapQueue,             \
+    Environment::handle_wrap_queue_)                                          \
+  V(Environment, req_wrap_queue_, Environment_ReqWrapQueue,                   \
+    Environment::req_wrap_queue_)                                             \
+  V(HandleWrap, handle_wrap_queue_, ListNode_HandleWrap,                      \
+    HandleWrap::handle_wrap_queue_)                                           \
+  V(Environment_HandleWrapQueue, head_, ListNode_HandleWrap,                  \
+    Environment::HandleWrapQueue::head_)                                      \
+  V(ListNode_HandleWrap, next_, uintptr_t, ListNode<HandleWrap>::next_)       \
+  V(ReqWrap, req_wrap_queue_, ListNode_ReqWrapQueue,                          \
+    ReqWrap<uv_req_t>::req_wrap_queue_)                                       \
+  V(Environment_ReqWrapQueue, head_, ListNode_ReqWrapQueue,                   \
+    Environment::ReqWrapQueue::head_)                                         \
+  V(ListNode_ReqWrap, next_, uintptr_t, ListNode<ReqWrap<uv_req_t>>::next_)
+
+extern "C" {
+int nodedbg_const_Environment__kContextEmbedderDataIndex__int;
+uintptr_t nodedbg_offset_ExternalString__data__uintptr_t;
+
+#define V(Class, Member, Type, Accessor)                                      \
+  NODE_EXTERN uintptr_t NODEDBG_OFFSET(Class, Member, Type);
+  NODE_OFFSET_POSTMORTEM_METADATA(V)
+#undef V
+}
+
+namespace node {
+
+int GenDebugSymbols() {
+  nodedbg_const_Environment__kContextEmbedderDataIndex__int =
+      Environment::kContextEmbedderDataIndex;
+
+  nodedbg_offset_ExternalString__data__uintptr_t = NODE_OFF_EXTSTR_DATA;
+
+  #define V(Class, Member, Type, Accessor)                                    \
+    NODEDBG_OFFSET(Class, Member, Type) = OffsetOf(&Accessor);
+    NODE_OFFSET_POSTMORTEM_METADATA(V)
+  #undef V
+
+  return 1;
+}
+
+int debug_symbols_generated = GenDebugSymbols();
+
+}  // namespace node

src/req-wrap.h

@@ -22,14 +22,19 @@ class ReqWrap : public AsyncWrap {
 
  private:
   friend class Environment;
+  friend int GenDebugSymbols();
   ListNode<ReqWrap> req_wrap_queue_;
 
  protected:
   // req_wrap_queue_ needs to be at a fixed offset from the start of the class
   // because it is used by ContainerOf to calculate the address of the embedding
-  // ReqWrap. ContainerOf compiles down to simple, fixed pointer arithmetic.
-  // sizeof(req_) depends on the type of T, so req_wrap_queue_ would
-  // no longer be at a fixed offset if it came after req_.
+  // ReqWrap. ContainerOf compiles down to simple, fixed pointer arithmetic. It
+  // is also used by src/node_postmortem_metadata.cc to calculate offsets and
+  // generate debug symbols for ReqWrap, which assumes that the position of
+  // members in memory are predictable. sizeof(req_) depends on the type of T,
+  // so req_wrap_queue_ would no longer be at a fixed offset if it came after
+  // req_. For more information please refer to
+  // `doc/guides/node-postmortem-support.md`
   T req_;
 };
 

src/util-inl.h

@@ -154,13 +154,17 @@ typename ListHead<T, M>::Iterator ListHead<T, M>::end() const {
   return Iterator(const_cast<ListNode<T>*>(&head_));
 }
 
+template <typename Inner, typename Outer>
+constexpr uintptr_t OffsetOf(Inner Outer::*field) {
+  return reinterpret_cast<uintptr_t>(&(static_cast<Outer*>(0)->*field));
+}
+
 template <typename Inner, typename Outer>
 ContainerOfHelper<Inner, Outer>::ContainerOfHelper(Inner Outer::*field,
                                                    Inner* pointer)
-    : pointer_(reinterpret_cast<Outer*>(
-          reinterpret_cast<uintptr_t>(pointer) -
-          reinterpret_cast<uintptr_t>(&(static_cast<Outer*>(0)->*field)))) {
-}
+    : pointer_(
+        reinterpret_cast<Outer*>(
+            reinterpret_cast<uintptr_t>(pointer) - OffsetOf(field))) {}
 
 template <typename Inner, typename Outer>
 template <typename TypeName>

src/util.h

@@ -159,6 +159,7 @@ class ListNode {
 
  private:
   template <typename U, ListNode<U> (U::*M)> friend class ListHead;
+  friend int GenDebugSymbols();
   ListNode* prev_;
   ListNode* next_;
   DISALLOW_COPY_AND_ASSIGN(ListNode);
@@ -190,6 +191,7 @@ class ListHead {
   inline Iterator end() const;
 
  private:
+  friend int GenDebugSymbols();
   ListNode<T> head_;
   DISALLOW_COPY_AND_ASSIGN(ListHead);
 };

test/cctest/node_test_fixture.h

@@ -5,6 +5,7 @@
 #include "gtest/gtest.h"
 #include "node.h"
 #include "node_platform.h"
+#include "node_internals.h"
 #include "env.h"
 #include "v8.h"
 #include "libplatform/libplatform.h"
@@ -73,6 +74,13 @@ class NodeTestFixture : public ::testing::Test {
     v8::Isolate::CreateParams params_;
     params_.array_buffer_allocator = allocator_.get();
     isolate_ = v8::Isolate::New(params_);
+
+    // As the TracingController is stored globally, we only need to create it
+    // one time for all tests.
+    if (node::tracing::TraceEventHelper::GetTracingController() == nullptr) {
+      node::tracing::TraceEventHelper::SetTracingController(
+          new v8::TracingController());
+    }
   }
 
   virtual void TearDown() {
@@ -93,4 +101,48 @@ class NodeTestFixture : public ::testing::Test {
       v8::ArrayBuffer::Allocator::NewDefaultAllocator()};
 };
 
+
+class EnvironmentTestFixture : public NodeTestFixture {
+ public:
+  class Env {
+   public:
+    Env(const v8::HandleScope& handle_scope, const Argv& argv) {
+      auto isolate = handle_scope.GetIsolate();
+      context_ = v8::Context::New(isolate);
+      CHECK(!context_.IsEmpty());
+      context_->Enter();
+
+      isolate_data_ = node::CreateIsolateData(isolate,
+                                              NodeTestFixture::CurrentLoop());
+      CHECK_NE(nullptr, isolate_data_);
+      environment_ = node::CreateEnvironment(isolate_data_,
+                                             context_,
+                                             1, *argv,
+                                             argv.nr_args(), *argv);
+      CHECK_NE(nullptr, environment_);
+    }
+
+    ~Env() {
+      environment_->CleanupHandles();
+      node::FreeEnvironment(environment_);
+      node::FreeIsolateData(isolate_data_);
+      context_->Exit();
+    }
+
+    node::Environment* operator*() const {
+      return environment_;
+    }
+
+    v8::Local<v8::Context> context()  const {
+      return context_;
+    }
+
+   private:
+    v8::Local<v8::Context> context_;
+    node::IsolateData* isolate_data_;
+    node::Environment* environment_;
+    DISALLOW_COPY_AND_ASSIGN(Env);
+  };
+};
+
 #endif  // TEST_CCTEST_NODE_TEST_FIXTURE_H_