tools/sources.py

#!/usr/bin/env vpython3
# Copyright 2019 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
'''A tool that helps ease libunwindstack updates by managing the
platform/system/core source files that are actually needed for libunwindstack to
compile.

To use this script, the //third_party/libunwindstack:libunwindstack must
be compilable. In practice this means that the tool must be run within a
Chromium checkout and that the libunwindstack target must be a transitive
dependency of some target normally compilable within the checkout
(e.g. chrome_public_apk).'''

import argparse
import os
import re
import subprocess
import sys

_LIBUNWINDSTACK_ROOT = os.path.abspath(
    os.path.join(os.path.dirname(__file__), os.pardir))
_LIBUNWINDSTACK_SRC_ROOT = os.path.join(_LIBUNWINDSTACK_ROOT, 'src')


def GenerateDepFiles(ninja_build_dir):
  '''Generates the dependency files that tell us which sources are used to
  compile libunwindstack.'''
  # We need to clean the build directory for two reasons:
  #
  # 1) This eliminates the risk that there are stale depfiles from previous
  #    times that the user built with -d keepdepfiles (including through this
  #    script).
  # 2) This ensures that the compilation actually happens, which is required to
  #    create the depfiles.
  #
  # Ideally, we'd use check_call to ensure that ninja -t clean
  # succeeds. However, ninja's clean tool exits with a return code under normal
  # circumstances because it can't clean up non-empty directories. Because of
  # this, we just ignore cleaning errors by using call() instead of
  # check_call().
  subprocess.call(['ninja', '-C', ninja_build_dir, '-t', 'clean'],
                  stdout=sys.stderr,
                  stderr=sys.stderr)

  subprocess.check_call([
      'ninja', '-C', ninja_build_dir,
      'third_party/libunwindstack:libunwindstack', '-d', 'keepdepfile'
  ],
                        stdout=sys.stderr,
                        stderr=sys.stderr)


def ExtractRequiredSources(ninja_build_dir):
  '''Assuming that the .o.d depfiles have already been generated by a build,
  parses the depfiles and returns a list of the C++ files in libunwindstack/src/
  that are needed to compile libunwindstack.'''
  aggregate_deps_process = subprocess.Popen([
      'find', '{}/obj/third_party/libunwindstack/'.format(ninja_build_dir),
      '-name', '*.o.d'
  ],
                                            stdout=subprocess.PIPE,
                                            stderr=sys.stderr)
  sources = subprocess.check_output(['xargs', 'cat'],
                                    stdin=aggregate_deps_process.stdout,
                                    stderr=sys.stderr).decode(
                                        sys.stdout.encoding)

  # Each of the .o.d files is actually in Makefile form, like:
  #
  # obj/third_party/libunwindstack/libunwindstack/ElfInterface.o: \
  #   ../../third_party/libunwindstack/src/libunwindstack/ElfInterface.cpp \
  #   ../../third_party/lzma_sdk/7zCrc.h \
  #   ../../third_party/lzma_sdk/7zTypes.h ../../third_party/lzma_sdk/Xz.h \
  #   ../../third_party/lzma_sdk/Sha256.h \
  #   ../../third_party/lzma_sdk/XzCrc64.h \
  #   ../../third_party/libunwindstack/src/libunwindstack/include/unwindstack/DwarfError.h \
  #   ../../third_party/libunwindstack/src/libunwindstack/include/unwindstack/DwarfSection.h \
  #   ...
  #
  # We're looking explicitly for the platform/system/core C++ source code
  # dependencies, so we use a regexp to extract these and ignore other
  # dependencies (e.g. src/third_party/lzma_sdk/) and .o target names.
  rel_sources = re.findall(r'third_party/libunwindstack/(src/\S+)', sources)
  return sorted(set(rel_sources))


def PrintGnFormattedSources(sources):
  print('sources = [')
  for source in sources:
    print('  "{}",'.format(source))
  print(']')


def PruneUnrequiredSources(required_sources):
  required_abs_sources = [
      os.path.join(_LIBUNWINDSTACK_ROOT, src) for src in required_sources
  ]
  current_sources = []

  for subdir, _, files in os.walk(_LIBUNWINDSTACK_SRC_ROOT):
    for f in files:
      current_sources.append(os.path.join(subdir, f))

  sources_to_remove = sorted(set(current_sources) - set(required_abs_sources))
  print('Removed the following sources:')
  for source in sources_to_remove:
    os.remove(source)
    print('{}'.format(source))


def Main():
  parser = argparse.ArgumentParser(description=__doc__)
  subparsers = parser.add_subparsers(dest='subcommand')
  print_parser = subparsers.add_parser(
      'print', help='Print the list of required sources to STDOUT.')
  prune_parser = subparsers.add_parser(
      'prune', help='Prune unrequired sources from the src/ directory.')

  parser.add_argument(
      'ninja_build_dir',
      help='Change to DIR before compiling (ninja build directory)')
  args = parser.parse_args()

  # Using the abspath here ensures there's no trailing slash.
  ninja_build_dir = os.path.abspath(args.ninja_build_dir)
  if not os.path.exists(ninja_build_dir):
    raise IOError(
        'Ninja build directory {} does not exist.'.format(ninja_build_dir))

  GenerateDepFiles(ninja_build_dir)
  required_sources = ExtractRequiredSources(ninja_build_dir)

  if args.subcommand == 'print':
    PrintGnFormattedSources(required_sources)
  elif args.subcommand == 'prune':
    PruneUnrequiredSources(required_sources)

  return 0


if __name__ == '__main__':
  sys.exit(Main())