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

@@ -299,6 +299,7 @@
         # node.gyp is added to the project by default.
         'common.gypi',
         '<(SHARED_INTERMEDIATE_DIR)/node_javascript.cc',
+        '<(SHARED_INTERMEDIATE_DIR)/node-debug-support.cc',
       ],
 
       'variables': {
@@ -974,7 +975,29 @@
             }]]
         }],
       ]
-    }
+    },
+    {
+      '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 +1,200 @@
+#!/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 os
+import fnmatch
+import re
+from glob import glob
+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
+
+  @property
+  def declare(self):
+    return '{type} {prefix}{name};'.format(
+      type=self.type_,
+      prefix=self._prefix,
+      name=self.name,
+    )
+
+  @property
+  def fill(self):
+    return '{prefix}{name} = {value};'.format(
+      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='nonstandard_offsetof(BaseObject, persistent_handle_)',
+    headers=['base_object-inl.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__Environment__handleWrapQueue',
+    value='nonstandard_offsetof(Environment, handle_wrap_queue_)',
+    headers=['env.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__HandleWrap__node',
+    value='nonstandard_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='nonstandard_offsetof(Environment, req_wrap_queue_)',
+    headers=['env.h'],
+    type_='size_t',
+  ),
+  DebugSymbol(
+    name='class__ReqWrap__node',
+    value='nonstandard_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.
+ */
+
+// Need to import standard headers before redefining private, otherwise it
+// won't compile
+{standard_includes}
+
+int GenDebugSymbol();
+
+#define private friend int GenDebugSymbol(); private
+
+#define nonstandard_offsetof(CLASS, FIELD) reinterpret_cast<uintptr_t>\
+        (&(static_cast<CLASS*>(0)->FIELD))
+
+{includes}
+
+{declare_symbols}
+
+namespace node {{
+
+int GenDebugSymbol() {{
+{fill_symbols}
+return 1;
+}}
+
+int debug_symbols_generated = GenDebugSymbol();
+
+}}
+'''
+
+
+def get_standard_includes():
+  '''
+  Try to find all standard C++ headers needed by node and its dependencies
+  '''
+  includes = ["algorithm", "array", "atomic", "bitset", "cctype", "climits",
+    "cmath", "cstdarg", "cstddef", "cstdint", "cstdio", "cstdlib", "cstring",
+    "ctime", "deque", "exception", "forward_list", "fstream", "functional",
+    "iomanip", "iosfwd", "iostream", "istream", "iterator", "limits", "list",
+    "map", "memory", "new", "ostream", "queue", "set", "sstream", "stack",
+    "streambuf", "string", "tuple", "type_traits", "typeinfo", "unordered_map",
+    "unordered_set", "utility", "vector"]
+  return includes
+
+
+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)
+
+  standard_includes = get_standard_includes()
+  standard_includes = ['#include <{0}>'.format(include) for include in standard_includes]
+  standard_includes = '\n'.join(standard_includes)
+
+  declare_symbols = '\n'.join([symbol.declare for symbol in debug_symbols])
+  fill_symbols = '\n'.join([symbol.fill for symbol in debug_symbols])
+
+  out.write(template.format(
+    filename=sys.argv[0],
+    includes=includes,
+    standard_includes=standard_includes,
+    declare_symbols=declare_symbols,
+    fill_symbols=fill_symbols,
+  ))
+
+
+if len(sys.argv) < 2:
+  print('usage: {0} output.cc'.format(sys.argv[0]))
+  sys.exit(2)
+
+
+create_symbols_file()