src, tools: add debug symbols for node internals

Before these changes, only V8 added debug symbols 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 a first steps towards empowering debug tools to
navigate Node's internals strucutres. 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 debug symbols are prefixed with node_dbg_.

Ref: nodejs/llnode#122
Ref: nodejs/post-mortem#46

node.gyp

@@ -172,6 +172,7 @@
 
       'dependencies': [
         'node_js2c#host',
+        'node_postmortem_metadata#host',
         'deps/nghttp2/nghttp2.gyp:nghttp2'
       ],
 
@@ -295,6 +296,7 @@
         # node.gyp is added to the project by default.
         'common.gypi',
         '<(SHARED_INTERMEDIATE_DIR)/node_javascript.cc',
+        '<(SHARED_INTERMEDIATE_DIR)/node-debug-support.cc',
       ],
 
       'defines': [
@@ -743,7 +745,29 @@
           'ldflags': [ '-I<(SHARED_INTERMEDIATE_DIR)' ]
         }],
       ]
-    }
+    },
+    {
+      'target_name': 'node_postmortem_metadata',
+      'type': 'none',
+      'toolsets': ['host'],
+      'actions': [
+        {
+          'action_name': 'gen-postmortem-metadata',
+          'process_outputs_as_sources': 1,
+          'inputs': [
+            './tools/gen-postmortem-metadata.py',
+          ],
+          'outputs': [
+            '<(SHARED_INTERMEDIATE_DIR)/node-debug-support.cc',
+          ],
+          'action': [
+            'python',
+            './tools/gen-postmortem-metadata.py',
+            '<@(_outputs)',
+          ]
+        }
+      ]
+    },
   ], # end targets
 
   'conditions': [

tools/gen-postmortem-metadata.py

@@ -0,0 +1,157 @@
+#!/usr/bin/env python
+
+#
+# gen-postmortem-metadata.py output_file.cc
+#
+# Creates debugging symbols to help naviage Node's internals using post-mortem
+# debugging tools.
+#
+
+import sys
+
+
+class DebugSymbol(object):
+  type_ = 'int'
+  _prefix = 'nodedbg_'
+
+  def __init__(self, name, value, headers=[], type_=None):
+    self.name = name
+    self.value = value
+    self.headers = headers
+    self.type_ = type_ or DebugSymbol.type_
+
+  @classmethod
+  def get_headers(cls, debug_symbols):
+    '''
+    Return a list of headers without duplicates, preserving the order they were
+    declared
+    '''
+    seen = set()
+    headers = [debug_symbol.headers for debug_symbol in debug_symbols]
+    headers = sum(headers, [])
+
+    result = []
+    for h in headers:
+      if not h in seen:
+        seen.add(h)
+        result.append(h)
+
+    return result
+
+  def __str__(self):
+    return '{type} {prefix}{name} = {value};'.format(
+      type=self.type_,
+      prefix=self._prefix,
+      name=self.name,
+      value=self.value,
+    )
+
+
+debug_symbols = [
+  DebugSymbol(
+    name='environment_context_idx_embedder_data',
+    value='Environment::kContextEmbedderDataIndex',
+    headers=['env.h'],
+    type_='int',
+  ),
+  DebugSymbol(
+    name='class__BaseObject__persistent_handle',
+    value='offsetof(BaseObject, persistent_handle_)',
+    headers=['base-object.h', 'base-object-inl.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__Environment__handleWrapQueue',
+    value='offsetof(Environment, handle_wrap_queue_)',
+    headers=['env.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__HandleWrap__node',
+    value='offsetof(HandleWrap, handle_wrap_queue_)',
+    headers=['handle_wrap.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__HandleWrapQueue__headOffset',
+    value='offsetof(Environment::HandleWrapQueue, head_)',
+    headers=['env.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__HandleWrapQueue__nextOffset',
+    value='offsetof(ListNode<HandleWrap>, next_)',
+    headers=['handle_wrap.h', 'util.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__Environment__reqWrapQueue',
+    value='offsetof(Environment, req_wrap_queue_)',
+    headers=['env.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__ReqWrap__node',
+    value='offsetof(ReqWrap<uv_req_t>, req_wrap_queue_)',
+    headers=['req-wrap.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__ReqWrapQueue__headOffset',
+    value='offsetof(Environment::ReqWrapQueue, head_)',
+    headers=['env.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__ReqWrapQueue__nextOffset',
+    value='offsetof(ListNode<ReqWrap<uv_req_t>>, next_)',
+    headers=['req-wrap.h', 'util.h'],
+    type_='size_t',
+  ),
+]
+
+
+template = '''
+/*
+ * This file is generated by {filename}.  Do not edit directly.
+ */
+
+#define _ALLOW_KEYWORD_MACROS 1
+#define private public
+#define protected public
+
+{includes}
+
+using namespace node;
+
+extern "C" {{
+{symbols}
+}}
+
+#undef private
+#undef protected
+#undef _ALLOW_KEYWORD_MACROS
+'''
+
+
+def create_symbols_file():
+  out = file(sys.argv[1], 'w')
+  headers = DebugSymbol.get_headers(debug_symbols)
+  includes = ['#include "{0}"'.format(header) for header in headers]
+  includes = '\n'.join(includes)
+
+  symbols = '\n'.join([str(symbol) for symbol in debug_symbols])
+
+  out.write(template.format(
+    filename=sys.argv[0],
+    includes=includes,
+    symbols=symbols,
+  ))
+
+
+if len(sys.argv) < 2:
+  print('usage: {0} output.cc'.format(sys.argv[0]))
+  sys.exit(2)
+
+
+create_symbols_file()