generate_def_file.py

"""Script to generate Chromium's Abseil .def file at roll time.

This script generates //third_party/abseil-app/absl/symbols_x64.def at Abseil
roll time.

Since Abseil doesn't export symbols, Chromium is forced to consider all
Abseil's symbols as publicly visible. On POSIX it is possible to use
-fvisibility=default but on Windows a .def file with all the symbols
is needed.

Unless you are on a Windows machine, you need to set up your Chromium
checkout for cross-compilation by following the instructions at
https://chromium.googlesource.com/chromium/src.git/+/master/docs/win_cross.md.
"""

import fnmatch
import logging
import os
import re
import subprocess
import tempfile
import time

# Matches a mangled symbol that has 'absl' in it, this should be a good
# enough heuristic to select Abseil symbols to list in the .def file.
ABSL_SYM_RE = re.compile(r'0* [BT] (?P<symbol>\?{1}[^\?].*absl.*)')


def _DebugOrRelease(is_debug):
  return 'dbg' if is_debug else 'rel'


def _GenerateDefFile(cpu, is_debug):
  """Generates a .def file for the absl component build on the specified CPU."""
  flavor = _DebugOrRelease(is_debug)
  gn_args = [
      'ffmpeg_branding = "Chrome"',
      'is_component_build = false',
      'is_debug = {}'.format(str(is_debug).lower()),
      'proprietary_codecs = true',
      'symbol_level = 0',
      'target_cpu = "{}"'.format(cpu),
      'target_os = "win"',
  ]

  with tempfile.TemporaryDirectory() as out_dir:
    logging.info('[%s - %s] Creating tmp out dir in %s', cpu, flavor, out_dir)
    subprocess.check_call(['gn', 'gen', out_dir, '--args=' + ' '.join(gn_args)],
                          cwd=os.getcwd())
    logging.info('[%s - %s] gn gen completed', cpu, flavor)
    subprocess.check_call(
        ['autoninja', '-C', out_dir, 'third_party/abseil-cpp:absl'],
        cwd=os.getcwd())
    logging.info('[%s - %s] autoninja completed', cpu, flavor)

    obj_files = []
    for root, _dirnames, filenames in os.walk(
        os.path.join(out_dir, 'obj', 'third_party', 'abseil-cpp')):
      matched_files = fnmatch.filter(filenames, '*.obj')
      obj_files.extend((os.path.join(root, f) for f in matched_files))

    logging.info('[%s - %s] Found %d object files.', cpu, flavor, len(obj_files))

    absl_symbols = set()
    for f in obj_files:
      stdout = subprocess.check_output(['llvm-nm-9', f], cwd=os.getcwd())
      for line in stdout.splitlines():
        match = re.match(ABSL_SYM_RE, line.decode('utf-8'))
        if match:
          absl_symbols.add(match.group('symbol'))

    logging.info('[%s - %s] Found %d absl symbols.', cpu, flavor, len(absl_symbols))

    def_file = os.path.join('third_party', 'abseil-cpp',
                            'symbols_{}_{}.def'.format(cpu, flavor))
    with open(def_file, 'w') as f:
      f.write('EXPORTS\n')
      for s in sorted(absl_symbols):
        f.write('    {}\n'.format(s))

    # Hack, it looks like there is a race in the directory cleanup.
    time.sleep(3)

  logging.info('[%s - %s] .def file successfully generated.', cpu, flavor)


if __name__ == '__main__':
  logging.getLogger().setLevel(logging.INFO)

  if not os.getcwd().endswith('chromium/src'):
    logging.error('Run this script from Chromium\'s src/ directory.')
    exit(1)

  _GenerateDefFile('x86', True)
  _GenerateDefFile('x86', False)
  _GenerateDefFile('x64', True)
  _GenerateDefFile('x64', False)
  _GenerateDefFile('arm64', True)
  _GenerateDefFile('arm64', False)