tools/linux/dump-static-initializers.py

   1 #!/usr/bin/env python
   2 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
   3 # Use of this source code is governed by a BSD-style license that can be
   4 # found in the LICENSE file.
   5
   6 """Dump functions called by static intializers in a Linux Release binary.
   7
   8 Usage example:
   9   tools/linux/dump-static-intializers.py out/Release/chrome
  10
  11 A brief overview of static initialization:
  12 1) the compiler writes out, per object file, a function that contains
  13    the static intializers for that file.
  14 2) the compiler also writes out a pointer to that function in a special
  15    section.
  16 3) at link time, the linker concatenates the function pointer sections
  17    into a single list of all initializers.
  18 4) at run time, on startup the binary runs all function pointers.
  19
  20 The functions in (1) all have mangled names of the form
  21   _GLOBAL__I_foobar.cc
  22 using objdump, we can disassemble those functions and dump all symbols that
  23 they reference.
  24 """
  25
  26 import optparse
  27 import re
  28 import subprocess
  29 import sys
  30
  31 # A map of symbol => informative text about it.
  32 NOTES = {
  33   '__cxa_atexit@plt': 'registers a dtor to run at exit',
  34   'std::__ioinit': '#includes <iostream>, use <ostream> instead',
  35 }
  36
  37 # Determine whether this is a git checkout (as opposed to e.g. svn).
  38 IS_GIT_WORKSPACE = (subprocess.Popen(
  39     ['git', 'rev-parse'], stderr=subprocess.PIPE).wait() == 0)
  40
  41 class Demangler(object):
  42   """A wrapper around c++filt to provide a function to demangle symbols."""
  43   def __init__(self):
  44     self.cppfilt = subprocess.Popen(['c++filt'],
  45                                     stdin=subprocess.PIPE,
  46                                     stdout=subprocess.PIPE)
  47
  48   def Demangle(self, sym):
  49     """Given mangled symbol |sym|, return its demangled form."""
  50     self.cppfilt.stdin.write(sym + '\n')
  51     return self.cppfilt.stdout.readline().strip()
  52
  53 # Matches for example: "cert_logger.pb.cc", capturing "cert_logger".
  54 protobuf_filename_re = re.compile(r'(.*)\.pb\.cc$')
  55 def QualifyFilenameAsProto(filename):
  56   """Attempt to qualify a bare |filename| with a src-relative path, assuming it
  57   is a protoc-generated file.  If a single match is found, it is returned.
  58   Otherwise the original filename is returned."""
  59   if not IS_GIT_WORKSPACE:
  60     return filename
  61   match = protobuf_filename_re.match(filename)
  62   if not match:
  63     return filename
  64   basename = match.groups(0)
  65   gitlsfiles = subprocess.Popen(
  66     ['git', 'ls-files', '--', '*/%s.proto' % basename],
  67     stdout=subprocess.PIPE)
  68   candidate = filename
  69   for line in gitlsfiles.stdout:
  70     if candidate != filename:
  71       return filename # Multiple hits, can't help.
  72     candidate = line.strip()
  73   return candidate
  74
  75 # Regex matching the substring of a symbol's demangled text representation most
  76 # likely to appear in a source file.
  77 # Example: "v8::internal::Builtins::InitBuiltinFunctionTable()" becomes
  78 # "InitBuiltinFunctionTable", since the first (optional & non-capturing) group
  79 # picks up any ::-qualification and the last fragment picks up a suffix that
  80 # starts with an opener.
  81 symbol_code_name_re = re.compile(r'^(?:[^(<[]*::)?([^:(<[]*).*?$')
  82 def QualifyFilename(filename, symbol):
  83   """Given a bare filename and a symbol that occurs in it, attempt to qualify
  84   it with a src-relative path.  If more than one file matches, return the
  85   original filename."""
  86   if not IS_GIT_WORKSPACE:
  87     return filename
  88   match = symbol_code_name_re.match(symbol)
  89   if not match:
  90     return filename
  91   symbol = match.group(1)
  92   gitgrep = subprocess.Popen(
  93     ['git', 'grep', '-l', symbol, '--', '*/%s' % filename],
  94     stdout=subprocess.PIPE)
  95   candidate = filename
  96   for line in gitgrep.stdout:
  97     if candidate != filename:  # More than one candidate; return bare filename.
  98       return filename
  99     candidate = line.strip()
 100   return candidate
 101
 102 # Regex matching nm output for the symbols we're interested in.
 103 # See test_ParseNmLine for examples.
 104 nm_re = re.compile(r'(\S+) (\S+) t (?:_ZN12)?_GLOBAL__(?:sub_)?I_(.*)')
 105 def ParseNmLine(line):
 106   """Given a line of nm output, parse static initializers as a
 107   (file, start, size) tuple."""
 108   match = nm_re.match(line)
 109   if match:
 110     addr, size, filename = match.groups()
 111     return (filename, int(addr, 16), int(size, 16))
 112
 113
 114 def test_ParseNmLine():
 115   """Verify the nm_re regex matches some sample lines."""
 116   parse = ParseNmLine(
 117     '0000000001919920 0000000000000008 t '
 118     '_ZN12_GLOBAL__I_safe_browsing_service.cc')
 119   assert parse == ('safe_browsing_service.cc', 26319136, 8), parse
 120
 121   parse = ParseNmLine(
 122     '00000000026b9eb0 0000000000000024 t '
 123     '_GLOBAL__sub_I_extension_specifics.pb.cc')
 124   assert parse == ('extension_specifics.pb.cc', 40607408, 36), parse
 125
 126 # Just always run the test; it is fast enough.
 127 test_ParseNmLine()
 128
 129
 130 def ParseNm(binary):
 131   """Given a binary, yield static initializers as (file, start, size) tuples."""
 132   nm = subprocess.Popen(['nm', '-S', binary], stdout=subprocess.PIPE)
 133   for line in nm.stdout:
 134     parse = ParseNmLine(line)
 135     if parse:
 136       yield parse
 137
 138 # Regex matching objdump output for the symbols we're interested in.
 139 # Example line:
 140 #     12354ab:  (disassembly, including <FunctionReference>)
 141 disassembly_re = re.compile(r'^\s+[0-9a-f]+:.*<(\S+)>')
 142 def ExtractSymbolReferences(binary, start, end):
 143   """Given a span of addresses, returns symbol references from disassembly."""
 144   cmd = ['objdump', binary, '--disassemble',
 145          '--start-address=0x%x' % start, '--stop-address=0x%x' % end]
 146   objdump = subprocess.Popen(cmd, stdout=subprocess.PIPE)
 147
 148   refs = set()
 149   for line in objdump.stdout:
 150     if '__static_initialization_and_destruction' in line:
 151       raise RuntimeError, ('code mentions '
 152                            '__static_initialization_and_destruction; '
 153                            'did you accidentally run this on a Debug binary?')
 154     match = disassembly_re.search(line)
 155     if match:
 156       (ref,) = match.groups()
 157       if ref.startswith('.LC') or ref.startswith('_DYNAMIC'):
 158         # Ignore these, they are uninformative.
 159         continue
 160       if ref.startswith('_GLOBAL__I_'):
 161         # Probably a relative jump within this function.
 162         continue
 163       refs.add(ref)
 164
 165   return sorted(refs)
 166
 167 def main():
 168   parser = optparse.OptionParser(usage='%prog [option] filename')
 169   parser.add_option('-d', '--diffable', dest='diffable',
 170                     action='store_true', default=False,
 171                     help='Prints the filename on each line, for more easily '
 172                          'diff-able output. (Used by sizes.py)')
 173   opts, args = parser.parse_args()
 174   if len(args) != 1:
 175     parser.error('missing filename argument')
 176     return 1
 177   binary = args[0]
 178
 179   demangler = Demangler()
 180   file_count = 0
 181   initializer_count = 0
 182
 183   files = ParseNm(binary)
 184   if opts.diffable:
 185     files = sorted(files)
 186   for filename, addr, size in files:
 187     file_count += 1
 188     ref_output = []
 189
 190     qualified_filename = QualifyFilenameAsProto(filename)
 191
 192     if size == 2:
 193       # gcc generates a two-byte 'repz retq' initializer when there is a
 194       # ctor even when the ctor is empty.  This is fixed in gcc 4.6, but
 195       # Android uses gcc 4.4.
 196       ref_output.append('[empty ctor, but it still has cost on gcc <4.6]')
 197     else:
 198       for ref in ExtractSymbolReferences(binary, addr, addr+size):
 199         initializer_count += 1
 200
 201         ref = demangler.Demangle(ref)
 202         if qualified_filename == filename:
 203           qualified_filename = QualifyFilename(filename, ref)
 204
 205         note = ''
 206         if ref in NOTES:
 207           note = NOTES[ref]
 208         elif ref.endswith('_2eproto()'):
 209           note = 'protocol compiler bug: crbug.com/105626'
 210
 211         if note:
 212           ref_output.append('%s [%s]' % (ref, note))
 213         else:
 214           ref_output.append(ref)
 215
 216     if opts.diffable:
 217       print '\n'.join('# ' + qualified_filename + ' ' + r for r in ref_output)
 218     else:
 219       print '%s (initializer offset 0x%x size 0x%x)' % (qualified_filename,
 220                                                         addr, size)
 221       print ''.join('  %s\n' % r for r in ref_output)
 222
 223   if opts.diffable:
 224     print '#',
 225   print 'Found %d static initializers in %d files.' % (initializer_count,
 226                                                        file_count)
 227
 228   return 0
 229
 230 if '__main__' == __name__:
 231   sys.exit(main())