src, test: node internals' postmortem metadata

Before these changes, only V8 added postmortem metadata to Node's
binary, limiting the possibilities for debugger's developers to add some
features that rely on investigating Node's internal structures.

These changes are first steps towards empowering debug tools to
navigate Node's internal structures. One example of what can be
achieved with this is shown at nodejs/llnode#122 (a command which prints
information about handles and requests on the queue for a core dump
file). Node postmortem metadata are prefixed with nodedbg_.

This also adds tests to validate if all postmortem metadata are
calculated correctly, plus some documentation on what is postmortem
metadata and a few care to be taken to avoid breaking it.

Ref: https://github.com/nodejs/llnode/pull/122
Ref: https://github.com/nodejs/post-mortem/issues/46

PR-URL: https://github.com/nodejs/node/pull/14901
Refs: https://github.com/nodejs/post-mortem/issues/46
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

1 files changed, 118 insertions, 0 deletions

diff --git a/src/node_postmortem_metadata.cc b/src/node_postmortem_metadata.cc
new file mode 100644
index 00000000000..4a463958f54
--- /dev/null
+++ b/src/node_postmortem_metadata.cc
@@ -0,0 +1,118 @@
+// Need to import standard headers before redefining private, otherwise it
+// won't compile.
+#include <algorithm>
+#include <array>
+#include <atomic>
+#include <bitset>
+#include <cctype>
+#include <climits>
+#include <cmath>
+#include <cstdarg>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <deque>
+#include <exception>
+#include <forward_list>
+#include <fstream>
+#include <functional>
+#include <iomanip>
+#include <iosfwd>
+#include <iostream>
+#include <istream>
+#include <iterator>
+#include <limits>
+#include <list>
+#include <map>
+#include <memory>
+#include <new>
+#include <ostream>
+#include <queue>
+#include <set>
+#include <sstream>
+#include <stack>
+#include <streambuf>
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <typeinfo>
+#include <unordered_map>
+#include <unordered_set>
+#include <utility>
+#include <vector>
+
+namespace node {
+// Forward declaration needed before redefining private.
+int GenDebugSymbols();
+}  // namespace node
+
+
+#define private friend int GenDebugSymbols(); private
+
+#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