build/toolchain/gcc_solink_wrapper.py

#!/usr/bin/env python
# Copyright 2015 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.

"""Runs 'ld -shared' and generates a .TOC file that's untouched when unchanged.

This script exists to avoid using complex shell commands in
gcc_toolchain.gni's tool("solink"), in case the host running the compiler
does not have a POSIX-like shell (e.g. Windows).
"""

import argparse
import os
import re
import subprocess
import sys


# When running on a Windows host and using a toolchain whose tools are
# actually wrapper scripts (i.e. .bat files on Windows) rather than binary
# executables, the "command" to run has to be prefixed with this magic.
# The GN toolchain definitions take care of that for when GN/Ninja is
# running the tool directly.  When that command is passed in to this
# script, it appears as a unitary string but needs to be split up so that
# just 'cmd' is the actual command given to Python's subprocess module.
BAT_PREFIX = 'cmd /c call '

def CommandToRun(command):
  if command[0].startswith(BAT_PREFIX):
    command = command[0].split(None, 3) + command[1:]
  return command


def CollectSONAME(args):
  """Replaces: readelf -d $sofile | grep SONAME"""
  toc = ''
  readelf = subprocess.Popen(CommandToRun([args.readelf, '-d', args.sofile]),
                             stdout=subprocess.PIPE, bufsize=-1)
  for line in readelf.stdout:
    if 'SONAME' in line:
      toc += line
  return readelf.wait(), toc


def CollectDynSym(args):
  """Replaces: nm --format=posix -g -D $sofile | cut -f1-2 -d' '"""
  toc = ''
  nm = subprocess.Popen(CommandToRun([
      args.nm, '--format=posix', '-g', '-D', args.sofile]),
                        stdout=subprocess.PIPE, bufsize=-1)
  for line in nm.stdout:
    toc += ' '.join(line.split(' ', 2)[:2]) + '\n'
  return nm.wait(), toc


def CollectTOC(args):
  result, toc = CollectSONAME(args)
  if result == 0:
    result, dynsym = CollectDynSym(args)
    toc += dynsym
  return result, toc


def UpdateTOC(tocfile, toc):
  if os.path.exists(tocfile):
    old_toc = open(tocfile, 'r').read()
  else:
    old_toc = None
  if toc != old_toc:
    open(tocfile, 'w').write(toc)


def main():
  parser = argparse.ArgumentParser(description=__doc__)
  parser.add_argument('--readelf',
                      required=True,
                      help='The readelf binary to run',
                      metavar='PATH')
  parser.add_argument('--nm',
                      required=True,
                      help='The nm binary to run',
                      metavar='PATH')
  parser.add_argument('--strip',
                      help='The strip binary to run',
                      metavar='PATH')
  parser.add_argument('--sofile',
                      required=True,
                      help='Shared object file produced by linking command',
                      metavar='FILE')
  parser.add_argument('--tocfile',
                      required=True,
                      help='Output table-of-contents file',
                      metavar='FILE')
  parser.add_argument('--output',
                      required=True,
                      help='Final output shared object file',
                      metavar='FILE')
  parser.add_argument('command', nargs='+',
                      help='Linking command')
  args = parser.parse_args()

  # First, run the actual link.
  result = subprocess.call(CommandToRun(args.command))
  if result != 0:
    return result

  # Next, generate the contents of the TOC file.
  result, toc = CollectTOC(args)
  if result != 0:
    return result

  # If there is an existing TOC file with identical contents, leave it alone.
  # Otherwise, write out the TOC file.
  UpdateTOC(args.tocfile, toc)

  # Finally, strip the linked shared object file (if desired).
  if args.strip:
    result = subprocess.call(CommandToRun([args.strip, '--strip-unneeded',
                                           '-o', args.output, args.sofile]))

  return result


if __name__ == "__main__":
  sys.exit(main())