Revert "[infra] Roll clang to match the version used by Flutter"

tools/clang/scripts/update.py

+#!/usr/bin/env python
+# Copyright (c) 2012 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.
+
+"""This script is used to download prebuilt clang binaries.
+
+It is also used by package.py to build the prebuilt clang binaries."""
+
+import argparse
+import distutils.spawn
+import glob
+import os
+import pipes
+import re
+import shutil
+import subprocess
+import stat
+import sys
+import tarfile
+import tempfile
+import time
+import urllib2
+import zipfile
+
+
+# Do NOT CHANGE this if you don't know what you're doing -- see
+# https://chromium.googlesource.com/chromium/src/+/master/docs/updating_clang.md
+# Reverting problematic clang rolls is safe, though.
+CLANG_REVISION = '282487'
+
+use_head_revision = 'LLVM_FORCE_HEAD_REVISION' in os.environ
+if use_head_revision:
+  CLANG_REVISION = 'HEAD'
+
+# This is incremented when pushing a new build of Clang at the same revision.
+CLANG_SUB_REVISION=1
+
+PACKAGE_VERSION = "%s-%s" % (CLANG_REVISION, CLANG_SUB_REVISION)
+
+# Path constants. (All of these should be absolute paths.)
+THIS_DIR = os.path.abspath(os.path.dirname(__file__))
+CHROMIUM_DIR = os.path.abspath(os.path.join(THIS_DIR, '..', '..', '..'))
+THIRD_PARTY_DIR = os.path.join(CHROMIUM_DIR, 'third_party')
+LLVM_DIR = os.path.join(THIRD_PARTY_DIR, 'llvm')
+LLVM_BOOTSTRAP_DIR = os.path.join(THIRD_PARTY_DIR, 'llvm-bootstrap')
+LLVM_BOOTSTRAP_INSTALL_DIR = os.path.join(THIRD_PARTY_DIR,
+                                          'llvm-bootstrap-install')
+LLVM_LTO_GOLD_PLUGIN_DIR = os.path.join(THIRD_PARTY_DIR, 'llvm-lto-gold-plugin')
+CHROME_TOOLS_SHIM_DIR = os.path.join(LLVM_DIR, 'tools', 'chrometools')
+LLVM_BUILD_DIR = os.path.join(CHROMIUM_DIR, 'third_party', 'llvm-build',
+                              'Release+Asserts')
+COMPILER_RT_BUILD_DIR = os.path.join(LLVM_BUILD_DIR, 'compiler-rt')
+CLANG_DIR = os.path.join(LLVM_DIR, 'tools', 'clang')
+LLD_DIR = os.path.join(LLVM_DIR, 'tools', 'lld')
+# compiler-rt is built as part of the regular LLVM build on Windows to get
+# the 64-bit runtime, and out-of-tree elsewhere.
+# TODO(thakis): Try to unify this.
+if sys.platform == 'win32':
+  COMPILER_RT_DIR = os.path.join(LLVM_DIR, 'projects', 'compiler-rt')
+else:
+  COMPILER_RT_DIR = os.path.join(LLVM_DIR, 'compiler-rt')
+LIBCXX_DIR = os.path.join(LLVM_DIR, 'projects', 'libcxx')
+LIBCXXABI_DIR = os.path.join(LLVM_DIR, 'projects', 'libcxxabi')
+LLVM_BUILD_TOOLS_DIR = os.path.abspath(
+    os.path.join(LLVM_DIR, '..', 'llvm-build-tools'))
+STAMP_FILE = os.path.normpath(
+    os.path.join(LLVM_DIR, '..', 'llvm-build', 'cr_build_revision'))
+BINUTILS_DIR = os.path.join(THIRD_PARTY_DIR, 'binutils')
+BINUTILS_BIN_DIR = os.path.join(BINUTILS_DIR, BINUTILS_DIR,
+                                'Linux_x64', 'Release', 'bin')
+BFD_PLUGINS_DIR = os.path.join(BINUTILS_DIR, 'Linux_x64', 'Release',
+                               'lib', 'bfd-plugins')
+VERSION = '4.0.0'
+ANDROID_NDK_DIR = os.path.join(
+    CHROMIUM_DIR, 'third_party', 'android_tools', 'ndk')
+
+# URL for pre-built binaries.
+CDS_URL = os.environ.get('CDS_CLANG_BUCKET_OVERRIDE',
+    'https://commondatastorage.googleapis.com/chromium-browser-clang')
+
+LLVM_REPO_URL='https://llvm.org/svn/llvm-project'
+if 'LLVM_REPO_URL' in os.environ:
+  LLVM_REPO_URL = os.environ['LLVM_REPO_URL']
+
+# Bump after VC updates.
+DIA_DLL = {
+  '2013': 'msdia120.dll',
+  '2015': 'msdia140.dll',
+}
+
+
+def DownloadUrl(url, output_file):
+  """Download url into output_file."""
+  CHUNK_SIZE = 4096
+  TOTAL_DOTS = 10
+  num_retries = 3
+  retry_wait_s = 5  # Doubled at each retry.
+
+  while True:
+    try:
+      sys.stdout.write('Downloading %s ' % url)
+      sys.stdout.flush()
+      response = urllib2.urlopen(url)
+      total_size = int(response.info().getheader('Content-Length').strip())
+      bytes_done = 0
+      dots_printed = 0
+      while True:
+        chunk = response.read(CHUNK_SIZE)
+        if not chunk:
+          break
+        output_file.write(chunk)
+        bytes_done += len(chunk)
+        num_dots = TOTAL_DOTS * bytes_done / total_size
+        sys.stdout.write('.' * (num_dots - dots_printed))
+        sys.stdout.flush()
+        dots_printed = num_dots
+      if bytes_done != total_size:
+        raise urllib2.URLError("only got %d of %d bytes" %
+                               (bytes_done, total_size))
+      print ' Done.'
+      return
+    except urllib2.URLError as e:
+      sys.stdout.write('\n')
+      print e
+      if num_retries == 0 or isinstance(e, urllib2.HTTPError) and e.code == 404:
+        raise e
+      num_retries -= 1
+      print 'Retrying in %d s ...' % retry_wait_s
+      time.sleep(retry_wait_s)
+      retry_wait_s *= 2
+
+
+def EnsureDirExists(path):
+  if not os.path.exists(path):
+    print "Creating directory %s" % path
+    os.makedirs(path)
+
+
+def DownloadAndUnpack(url, output_dir):
+  with tempfile.TemporaryFile() as f:
+    DownloadUrl(url, f)
+    f.seek(0)
+    EnsureDirExists(output_dir)
+    if url.endswith('.zip'):
+      zipfile.ZipFile(f).extractall(path=output_dir)
+    else:
+      tarfile.open(mode='r:gz', fileobj=f).extractall(path=output_dir)
+
+
+def ReadStampFile(path=STAMP_FILE):
+  """Return the contents of the stamp file, or '' if it doesn't exist."""
+  try:
+    with open(path, 'r') as f:
+      return f.read().rstrip()
+  except IOError:
+    return ''
+
+
+def WriteStampFile(s, path=STAMP_FILE):
+  """Write s to the stamp file."""
+  EnsureDirExists(os.path.dirname(path))
+  with open(path, 'w') as f:
+    f.write(s)
+    f.write('\n')
+
+
+def GetSvnRevision(svn_repo):
+  """Returns current revision of the svn repo at svn_repo."""
+  if sys.platform == 'darwin':
+    # mac_files toolchain must be set for hermetic builds.
+    root = os.path.dirname(os.path.dirname(os.path.dirname(
+        os.path.dirname(__file__))))
+    sys.path.append(os.path.join(root, 'build'))
+    import mac_toolchain
+
+    mac_toolchain.SetToolchainEnvironment()
+  svn_info = subprocess.check_output('svn info ' + svn_repo, shell=True)
+  m = re.search(r'Revision: (\d+)', svn_info)
+  return m.group(1)
+
+
+def RmTree(dir):
+  """Delete dir."""
+  def ChmodAndRetry(func, path, _):
+    # Subversion can leave read-only files around.
+    if not os.access(path, os.W_OK):
+      os.chmod(path, stat.S_IWUSR)
+      return func(path)
+    raise
+
+  shutil.rmtree(dir, onerror=ChmodAndRetry)
+
+
+def RmCmakeCache(dir):
+  """Delete CMake cache related files from dir."""
+  for dirpath, dirs, files in os.walk(dir):
+    if 'CMakeCache.txt' in files:
+      os.remove(os.path.join(dirpath, 'CMakeCache.txt'))
+    if 'CMakeFiles' in dirs:
+      RmTree(os.path.join(dirpath, 'CMakeFiles'))
+
+
+def RunCommand(command, msvc_arch=None, env=None, fail_hard=True):
+  """Run command and return success (True) or failure; or if fail_hard is
+     True, exit on failure.  If msvc_arch is set, runs the command in a
+     shell with the msvc tools for that architecture."""
+
+  if msvc_arch and sys.platform == 'win32':
+    command = GetVSVersion().SetupScript(msvc_arch) + ['&&'] + command
+
+  # https://docs.python.org/2/library/subprocess.html:
+  # "On Unix with shell=True [...] if args is a sequence, the first item
+  # specifies the command string, and any additional items will be treated as
+  # additional arguments to the shell itself.  That is to say, Popen does the
+  # equivalent of:
+  #   Popen(['/bin/sh', '-c', args[0], args[1], ...])"
+  #
+  # We want to pass additional arguments to command[0], not to the shell,
+  # so manually join everything into a single string.
+  # Annoyingly, for "svn co url c:\path", pipes.quote() thinks that it should
+  # quote c:\path but svn can't handle quoted paths on Windows.  Since on
+  # Windows follow-on args are passed to args[0] instead of the shell, don't
+  # do the single-string transformation there.
+  if sys.platform != 'win32':
+    command = ' '.join([pipes.quote(c) for c in command])
+  print 'Running', command
+  if subprocess.call(command, env=env, shell=True) == 0:
+    return True
+  print 'Failed.'
+  if fail_hard:
+    sys.exit(1)
+  return False
+
+
+def CopyFile(src, dst):
+  """Copy a file from src to dst."""
+  print "Copying %s to %s" % (src, dst)
+  shutil.copy(src, dst)
+
+
+def CopyDirectoryContents(src, dst, filename_filter=None):
+  """Copy the files from directory src to dst
+  with an optional filename filter."""
+  dst = os.path.realpath(dst)  # realpath() in case dst ends in /..
+  EnsureDirExists(dst)
+  for root, _, files in os.walk(src):
+    for f in files:
+      if filename_filter and not re.match(filename_filter, f):
+        continue
+      CopyFile(os.path.join(root, f), dst)
+
+
+def Checkout(name, url, dir):
+  """Checkout the SVN module at url into dir. Use name for the log message."""
+  print "Checking out %s r%s into '%s'" % (name, CLANG_REVISION, dir)
+
+  command = ['svn', 'checkout', '--force', url + '@' + CLANG_REVISION, dir]
+  if RunCommand(command, fail_hard=False):
+    return
+
+  if os.path.isdir(dir):
+    print "Removing %s." % (dir)
+    RmTree(dir)
+
+  print "Retrying."
+  RunCommand(command)
+
+
+def DeleteChromeToolsShim():
+  OLD_SHIM_DIR = os.path.join(LLVM_DIR, 'tools', 'zzz-chrometools')
+  shutil.rmtree(OLD_SHIM_DIR, ignore_errors=True)
+  shutil.rmtree(CHROME_TOOLS_SHIM_DIR, ignore_errors=True)
+
+
+def CreateChromeToolsShim():
+  """Hooks the Chrome tools into the LLVM build.
+
+  Several Chrome tools have dependencies on LLVM/Clang libraries. The LLVM build
+  detects implicit tools in the tools subdirectory, so this helper install a
+  shim CMakeLists.txt that forwards to the real directory for the Chrome tools.
+
+  Note that the shim directory name intentionally has no - or _. The implicit
+  tool detection logic munges them in a weird way."""
+  assert not any(i in os.path.basename(CHROME_TOOLS_SHIM_DIR) for i in '-_')
+  os.mkdir(CHROME_TOOLS_SHIM_DIR)
+  with file(os.path.join(CHROME_TOOLS_SHIM_DIR, 'CMakeLists.txt'), 'w') as f:
+    f.write('# Automatically generated by tools/clang/scripts/update.py. ' +
+            'Do not edit.\n')
+    f.write('# Since tools/clang is located in another directory, use the \n')
+    f.write('# two arg version to specify where build artifacts go. CMake\n')
+    f.write('# disallows reuse of the same binary dir for multiple source\n')
+    f.write('# dirs, so the build artifacts need to go into a subdirectory.\n')
+    f.write('# dirs, so the build artifacts need to go into a subdirectory.\n')
+    f.write('if (CHROMIUM_TOOLS_SRC)\n')
+    f.write('  add_subdirectory(${CHROMIUM_TOOLS_SRC} ' +
+              '${CMAKE_CURRENT_BINARY_DIR}/a)\n')
+    f.write('endif (CHROMIUM_TOOLS_SRC)\n')
+
+
+def DownloadHostGcc(args):
+  """Downloads gcc 4.8.5 and makes sure args.gcc_toolchain is set."""
+  if not sys.platform.startswith('linux') or args.gcc_toolchain:
+    return
+  # Unconditionally download a prebuilt gcc to guarantee the included libstdc++
+  # works on Ubuntu Precise.
+  gcc_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'gcc485precise')
+  if not os.path.exists(gcc_dir):
+    print 'Downloading pre-built GCC 4.8.5...'
+    DownloadAndUnpack(
+        CDS_URL + '/tools/gcc485precise.tgz', LLVM_BUILD_TOOLS_DIR)
+  args.gcc_toolchain = gcc_dir
+
+
+def AddCMakeToPath():
+  """Download CMake and add it to PATH."""
+  if sys.platform == 'win32':
+    zip_name = 'cmake-3.4.3-win32-x86.zip'
+    cmake_dir = os.path.join(LLVM_BUILD_TOOLS_DIR,
+                             'cmake-3.4.3-win32-x86', 'bin')
+  else:
+    suffix = 'Darwin' if sys.platform == 'darwin' else 'Linux'
+    zip_name = 'cmake343_%s.tgz' % suffix
+    cmake_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'cmake343', 'bin')
+  if not os.path.exists(cmake_dir):
+    DownloadAndUnpack(CDS_URL + '/tools/' + zip_name, LLVM_BUILD_TOOLS_DIR)
+  os.environ['PATH'] = cmake_dir + os.pathsep + os.environ.get('PATH', '')
+
+
+def AddGnuWinToPath():
+  """Download some GNU win tools and add them to PATH."""
+  if sys.platform != 'win32':
+    return
+
+  gnuwin_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'gnuwin')
+  GNUWIN_VERSION = '5'
+  GNUWIN_STAMP = os.path.join(gnuwin_dir, 'stamp')
+  if ReadStampFile(GNUWIN_STAMP) == GNUWIN_VERSION:
+    print 'GNU Win tools already up to date.'
+  else:
+    zip_name = 'gnuwin-%s.zip' % GNUWIN_VERSION
+    DownloadAndUnpack(CDS_URL + '/tools/' + zip_name, LLVM_BUILD_TOOLS_DIR)
+    WriteStampFile(GNUWIN_VERSION, GNUWIN_STAMP)
+
+  os.environ['PATH'] = gnuwin_dir + os.pathsep + os.environ.get('PATH', '')
+
+
+vs_version = None
+def GetVSVersion():
+  global vs_version
+  if vs_version:
+    return vs_version
+
+  # Try using the toolchain in depot_tools.
+  # This sets environment variables used by SelectVisualStudioVersion below.
+  sys.path.append(os.path.join(CHROMIUM_DIR, 'build'))
+  import vs_toolchain
+  vs_toolchain.SetEnvironmentAndGetRuntimeDllDirs()
+
+  # Use gyp to find the MSVS installation, either in depot_tools as per above,
+  # or a system-wide installation otherwise.
+  sys.path.append(os.path.join(CHROMIUM_DIR, 'tools', 'gyp', 'pylib'))
+  import gyp.MSVSVersion
+  vs_version = gyp.MSVSVersion.SelectVisualStudioVersion(
+      vs_toolchain.GetVisualStudioVersion())
+  return vs_version
+
+
+def CopyDiaDllTo(target_dir):
+  # This script always wants to use the 64-bit msdia*.dll.
+  dia_path = os.path.join(GetVSVersion().Path(), 'DIA SDK', 'bin', 'amd64')
+  dia_dll = os.path.join(dia_path, DIA_DLL[GetVSVersion().ShortName()])
+  CopyFile(dia_dll, target_dir)
+
+
+def VeryifyVersionOfBuiltClangMatchesVERSION():
+  """Checks that `clang --version` outputs VERSION.  If this fails, VERSION
+  in this file is out-of-date and needs to be updated (possibly in an
+  `if use_head_revision:` block in main() first)."""
+  clang = os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')
+  if sys.platform == 'win32':
+    # TODO: Parse `clang-cl /?` output for built clang's version and check that
+    # to check the binary we're actually shipping? But clang-cl.exe is just
+    # a copy of clang.exe, so this does check the same thing.
+    clang += '.exe'
+  version_out = subprocess.check_output([clang, '--version'])
+  version_out = re.match(r'clang version ([0-9.]+)', version_out).group(1)
+  if version_out != VERSION:
+    print ('unexpected clang version %s (not %s), update VERSION in update.py'
+           % (version_out, VERSION))
+    sys.exit(1)
+
+
+def UpdateClang(args):
+  print 'Updating Clang to %s...' % PACKAGE_VERSION
+
+  need_gold_plugin = 'LLVM_DOWNLOAD_GOLD_PLUGIN' in os.environ or (
+      sys.platform.startswith('linux') and
+      'buildtype=Official' in os.environ.get('GYP_DEFINES', '') and
+      'branding=Chrome' in os.environ.get('GYP_DEFINES', ''))
+
+  if ReadStampFile() == PACKAGE_VERSION and not args.force_local_build:
+    print 'Clang is already up to date.'
+    if not need_gold_plugin or os.path.exists(
+        os.path.join(LLVM_BUILD_DIR, "lib/LLVMgold.so")):
+      return 0
+
+  # Reset the stamp file in case the build is unsuccessful.
+  WriteStampFile('')
+
+  if not args.force_local_build:
+    cds_file = "clang-%s.tgz" %  PACKAGE_VERSION
+    if sys.platform == 'win32' or sys.platform == 'cygwin':
+      cds_full_url = CDS_URL + '/Win/' + cds_file
+    elif sys.platform == 'darwin':
+      cds_full_url = CDS_URL + '/Mac/' + cds_file
+    else:
+      assert sys.platform.startswith('linux')
+      cds_full_url = CDS_URL + '/Linux_x64/' + cds_file
+
+    print 'Downloading prebuilt clang'
+    if os.path.exists(LLVM_BUILD_DIR):
+      RmTree(LLVM_BUILD_DIR)
+    try:
+      DownloadAndUnpack(cds_full_url, LLVM_BUILD_DIR)
+      print 'clang %s unpacked' % PACKAGE_VERSION
+      if sys.platform == 'win32':
+        CopyDiaDllTo(os.path.join(LLVM_BUILD_DIR, 'bin'))
+      # Download the gold plugin if requested to by an environment variable.
+      # This is used by the CFI ClusterFuzz bot, and it's required for official
+      # builds on linux.
+      if need_gold_plugin:
+        RunCommand(['python', CHROMIUM_DIR+'/build/download_gold_plugin.py'])
+      WriteStampFile(PACKAGE_VERSION)
+      return 0
+    except urllib2.URLError:
+      print 'Failed to download prebuilt clang %s' % cds_file
+      print 'Use --force-local-build if you want to build locally.'
+      print 'Exiting.'
+      return 1
+
+  if args.with_android and not os.path.exists(ANDROID_NDK_DIR):
+    print 'Android NDK not found at ' + ANDROID_NDK_DIR
+    print 'The Android NDK is needed to build a Clang whose -fsanitize=address'
+    print 'works on Android. See '
+    print 'https://www.chromium.org/developers/how-tos/android-build-instructions'
+    print 'for how to install the NDK, or pass --without-android.'
+    return 1
+
+  DownloadHostGcc(args)
+  AddCMakeToPath()
+  AddGnuWinToPath()
+
+  DeleteChromeToolsShim()
+
+  Checkout('LLVM', LLVM_REPO_URL + '/llvm/trunk', LLVM_DIR)
+  Checkout('Clang', LLVM_REPO_URL + '/cfe/trunk', CLANG_DIR)
+  if sys.platform == 'win32' or use_head_revision:
+    Checkout('LLD', LLVM_REPO_URL + '/lld/trunk', LLD_DIR)
+  Checkout('compiler-rt', LLVM_REPO_URL + '/compiler-rt/trunk', COMPILER_RT_DIR)
+  if sys.platform == 'darwin':
+    # clang needs a libc++ checkout, else -stdlib=libc++ won't find includes
+    # (i.e. this is needed for bootstrap builds).
+    Checkout('libcxx', LLVM_REPO_URL + '/libcxx/trunk', LIBCXX_DIR)
+    # We used to check out libcxxabi on OS X; we no longer need that.
+    if os.path.exists(LIBCXXABI_DIR):
+      RmTree(LIBCXXABI_DIR)
+
+  cc, cxx = None, None
+  libstdcpp = None
+  if args.gcc_toolchain:  # This option is only used on Linux.
+    # Use the specified gcc installation for building.
+    cc = os.path.join(args.gcc_toolchain, 'bin', 'gcc')
+    cxx = os.path.join(args.gcc_toolchain, 'bin', 'g++')
+
+    if not os.access(cc, os.X_OK):
+      print 'Invalid --gcc-toolchain: "%s"' % args.gcc_toolchain
+      print '"%s" does not appear to be valid.' % cc
+      return 1
+
+    # Set LD_LIBRARY_PATH to make auxiliary targets (tablegen, bootstrap
+    # compiler, etc.) find the .so.
+    libstdcpp = subprocess.check_output(
+        [cxx, '-print-file-name=libstdc++.so.6']).rstrip()
+    os.environ['LD_LIBRARY_PATH'] = os.path.dirname(libstdcpp)
+
+  cflags = []
+  cxxflags = []
+  ldflags = []
+
+  base_cmake_args = ['-GNinja',
+                     '-DCMAKE_BUILD_TYPE=Release',
+                     '-DLLVM_ENABLE_ASSERTIONS=ON',
+                     '-DLLVM_ENABLE_THREADS=OFF',
+                     '-DLLVM_ENABLE_TIMESTAMPS=OFF',
+                     # Statically link MSVCRT to avoid DLL dependencies.
+                     '-DLLVM_USE_CRT_RELEASE=MT',
+                     ]
+
+  binutils_incdir = ''
+  if sys.platform.startswith('linux'):
+    binutils_incdir = os.path.join(BINUTILS_DIR, 'Linux_x64/Release/include')
+
+  if args.bootstrap:
+    print 'Building bootstrap compiler'
+    EnsureDirExists(LLVM_BOOTSTRAP_DIR)
+    os.chdir(LLVM_BOOTSTRAP_DIR)
+    bootstrap_args = base_cmake_args + [
+        '-DLLVM_BINUTILS_INCDIR=' + binutils_incdir,
+        '-DLLVM_TARGETS_TO_BUILD=host',
+        '-DCMAKE_INSTALL_PREFIX=' + LLVM_BOOTSTRAP_INSTALL_DIR,
+        '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
+        '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags),
+        ]
+    if cc is not None:  bootstrap_args.append('-DCMAKE_C_COMPILER=' + cc)
+    if cxx is not None: bootstrap_args.append('-DCMAKE_CXX_COMPILER=' + cxx)
+    RmCmakeCache('.')
+    RunCommand(['cmake'] + bootstrap_args + [LLVM_DIR], msvc_arch='x64')
+    RunCommand(['ninja'], msvc_arch='x64')
+    if args.run_tests:
+      if sys.platform == 'win32':
+        CopyDiaDllTo(os.path.join(LLVM_BOOTSTRAP_DIR, 'bin'))
+      RunCommand(['ninja', 'check-all'], msvc_arch='x64')
+    RunCommand(['ninja', 'install'], msvc_arch='x64')
+    if args.gcc_toolchain:
+      # Copy that gcc's stdlibc++.so.6 to the build dir, so the bootstrap
+      # compiler can start.
+      CopyFile(libstdcpp, os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'lib'))
+
+    if sys.platform == 'win32':
+      cc = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang-cl.exe')
+      cxx = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang-cl.exe')
+      # CMake has a hard time with backslashes in compiler paths:
+      # https://stackoverflow.com/questions/13050827
+      cc = cc.replace('\\', '/')
+      cxx = cxx.replace('\\', '/')
+    else:
+      cc = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang')
+      cxx = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang++')
+
+    if args.gcc_toolchain:
+      # Tell the bootstrap compiler to use a specific gcc prefix to search
+      # for standard library headers and shared object files.
+      cflags = ['--gcc-toolchain=' + args.gcc_toolchain]
+      cxxflags = ['--gcc-toolchain=' + args.gcc_toolchain]
+    print 'Building final compiler'
+
+  # Build LLVM gold plugin with LTO. That speeds up the linker by ~10%.
+  # We only use LTO for Linux now.
+  if args.bootstrap and args.lto_gold_plugin:
+    print 'Building LTO LLVM Gold plugin'
+    if os.path.exists(LLVM_LTO_GOLD_PLUGIN_DIR):
+      RmTree(LLVM_LTO_GOLD_PLUGIN_DIR)
+    EnsureDirExists(LLVM_LTO_GOLD_PLUGIN_DIR)
+    os.chdir(LLVM_LTO_GOLD_PLUGIN_DIR)
+
+    # Create a symlink to LLVMgold.so build in the previous step so that ar
+    # and ranlib could find it while linking LLVMgold.so with LTO.
+    EnsureDirExists(BFD_PLUGINS_DIR)
+    RunCommand(['ln', '-sf',
+                os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'lib', 'LLVMgold.so'),
+                os.path.join(BFD_PLUGINS_DIR, 'LLVMgold.so')])
+
+    lto_cflags = ['-flto']
+    lto_ldflags = ['-fuse-ld=gold']
+    if args.gcc_toolchain:
+      # Tell the bootstrap compiler to use a specific gcc prefix to search
+      # for standard library headers and shared object files.
+      lto_cflags += ['--gcc-toolchain=' + args.gcc_toolchain]
+    lto_cmake_args = base_cmake_args + [
+        '-DLLVM_BINUTILS_INCDIR=' + binutils_incdir,
+        '-DCMAKE_C_COMPILER=' + cc,
+        '-DCMAKE_CXX_COMPILER=' + cxx,
+        '-DCMAKE_C_FLAGS=' + ' '.join(lto_cflags),
+        '-DCMAKE_CXX_FLAGS=' + ' '.join(lto_cflags),
+        '-DCMAKE_EXE_LINKER_FLAGS=' + ' '.join(lto_ldflags),
+        '-DCMAKE_SHARED_LINKER_FLAGS=' + ' '.join(lto_ldflags),
+        '-DCMAKE_MODULE_LINKER_FLAGS=' + ' '.join(lto_ldflags)]
+
+    # We need to use the proper binutils which support LLVM Gold plugin.
+    lto_env = os.environ.copy()
+    lto_env['PATH'] = BINUTILS_BIN_DIR + os.pathsep + lto_env.get('PATH', '')
+
+    RmCmakeCache('.')
+    RunCommand(['cmake'] + lto_cmake_args + [LLVM_DIR], env=lto_env)
+    RunCommand(['ninja', 'LLVMgold'], env=lto_env)
+
+
+  # LLVM uses C++11 starting in llvm 3.5. On Linux, this means libstdc++4.7+ is
+  # needed, on OS X it requires libc++. clang only automatically links to libc++
+  # when targeting OS X 10.9+, so add stdlib=libc++ explicitly so clang can run
+  # on OS X versions as old as 10.7.
+  deployment_target = ''
+
+  if sys.platform == 'darwin' and args.bootstrap:
+    # When building on 10.9, /usr/include usually doesn't exist, and while
+    # Xcode's clang automatically sets a sysroot, self-built clangs don't.
+    cflags = ['-isysroot', subprocess.check_output(
+        ['xcrun', '--show-sdk-path']).rstrip()]
+    cxxflags = ['-stdlib=libc++'] + cflags
+    ldflags += ['-stdlib=libc++']
+    deployment_target = '10.7'
+    # Running libc++ tests takes a long time. Since it was only needed for
+    # the install step above, don't build it as part of the main build.
+    # This makes running package.py over 10% faster (30 min instead of 34 min)
+    RmTree(LIBCXX_DIR)
+
+  # Build clang.
+
+  # If building at head, define a macro that plugins can use for #ifdefing
+  # out code that builds at head, but not at CLANG_REVISION or vice versa.
+  if use_head_revision:
+    cflags += ['-DLLVM_FORCE_HEAD_REVISION']
+    cxxflags += ['-DLLVM_FORCE_HEAD_REVISION']
+
+  CreateChromeToolsShim()
+
+  deployment_env = None
+  if deployment_target:
+    deployment_env = os.environ.copy()
+    deployment_env['MACOSX_DEPLOYMENT_TARGET'] = deployment_target
+
+  cmake_args = []
+  # TODO(thakis): Unconditionally append this to base_cmake_args instead once
+  # compiler-rt can build with clang-cl on Windows (http://llvm.org/PR23698)
+  cc_args = base_cmake_args if sys.platform != 'win32' else cmake_args
+  if cc is not None:  cc_args.append('-DCMAKE_C_COMPILER=' + cc)
+  if cxx is not None: cc_args.append('-DCMAKE_CXX_COMPILER=' + cxx)
+  cmake_args += base_cmake_args + [
+      '-DLLVM_BINUTILS_INCDIR=' + binutils_incdir,
+      '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
+      '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags),
+      '-DCMAKE_EXE_LINKER_FLAGS=' + ' '.join(ldflags),
+      '-DCMAKE_SHARED_LINKER_FLAGS=' + ' '.join(ldflags),
+      '-DCMAKE_MODULE_LINKER_FLAGS=' + ' '.join(ldflags),
+      '-DCMAKE_INSTALL_PREFIX=' + LLVM_BUILD_DIR,
+      # TODO(thakis): Remove this once official builds pass -Wl,--build-id
+      # explicitly, https://crbug.com/622775
+      '-DENABLE_LINKER_BUILD_ID=ON',
+      '-DCHROMIUM_TOOLS_SRC=%s' % os.path.join(CHROMIUM_DIR, 'tools', 'clang'),
+      '-DCHROMIUM_TOOLS=%s' % ';'.join(args.tools)]
+
+  EnsureDirExists(LLVM_BUILD_DIR)
+  os.chdir(LLVM_BUILD_DIR)
+  RmCmakeCache('.')
+  RunCommand(['cmake'] + cmake_args + [LLVM_DIR],
+             msvc_arch='x64', env=deployment_env)
+
+  if args.gcc_toolchain:
+    # Copy in the right stdlibc++.so.6 so clang can start.
+    if not os.path.exists(os.path.join(LLVM_BUILD_DIR, 'lib')):
+      os.mkdir(os.path.join(LLVM_BUILD_DIR, 'lib'))
+    libstdcpp = subprocess.check_output(
+        [cxx] + cxxflags + ['-print-file-name=libstdc++.so.6']).rstrip()
+    CopyFile(libstdcpp, os.path.join(LLVM_BUILD_DIR, 'lib'))
+
+  RunCommand(['ninja'], msvc_arch='x64')
+
+  if args.tools:
+    # If any Chromium tools were built, install those now.
+    RunCommand(['ninja', 'cr-install'], msvc_arch='x64')
+
+  if sys.platform == 'darwin':
+    # See http://crbug.com/256342
+    RunCommand(['strip', '-x', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
+  elif sys.platform.startswith('linux'):
+    RunCommand(['strip', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
+
+  VeryifyVersionOfBuiltClangMatchesVERSION()
+
+  # Do an out-of-tree build of compiler-rt.
+  # On Windows, this is used to get the 32-bit ASan run-time.
+  # TODO(hans): Remove once the regular build above produces this.
+  # On Mac and Linux, this is used to get the regular 64-bit run-time.
+  # Do a clobbered build due to cmake changes.
+  if os.path.isdir(COMPILER_RT_BUILD_DIR):
+    RmTree(COMPILER_RT_BUILD_DIR)
+  os.makedirs(COMPILER_RT_BUILD_DIR)
+  os.chdir(COMPILER_RT_BUILD_DIR)
+  # TODO(thakis): Add this once compiler-rt can build with clang-cl (see
+  # above).
+  #if args.bootstrap and sys.platform == 'win32':
+    # The bootstrap compiler produces 64-bit binaries by default.
+    #cflags += ['-m32']
+    #cxxflags += ['-m32']
+  compiler_rt_args = base_cmake_args + [
+      '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
+      '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags)]
+  if sys.platform == 'darwin':
+    compiler_rt_args += ['-DCOMPILER_RT_ENABLE_IOS=ON']
+  if sys.platform != 'win32':
+    compiler_rt_args += ['-DLLVM_CONFIG_PATH=' +
+                         os.path.join(LLVM_BUILD_DIR, 'bin', 'llvm-config'),
+                        '-DSANITIZER_MIN_OSX_VERSION="10.7"']
+  # compiler-rt is part of the llvm checkout on Windows but a stand-alone
+  # directory elsewhere, see the TODO above COMPILER_RT_DIR.
+  RmCmakeCache('.')
+  RunCommand(['cmake'] + compiler_rt_args +
+             [LLVM_DIR if sys.platform == 'win32' else COMPILER_RT_DIR],
+             msvc_arch='x86', env=deployment_env)
+  RunCommand(['ninja', 'compiler-rt'], msvc_arch='x86')
+
+  # Copy select output to the main tree.
+  # TODO(hans): Make this (and the .gypi and .isolate files) version number
+  # independent.
+  if sys.platform == 'win32':
+    platform = 'windows'
+  elif sys.platform == 'darwin':
+    platform = 'darwin'
+  else:
+    assert sys.platform.startswith('linux')
+    platform = 'linux'
+  asan_rt_lib_src_dir = os.path.join(COMPILER_RT_BUILD_DIR, 'lib', platform)
+  if sys.platform == 'win32':
+    # TODO(thakis): This too is due to compiler-rt being part of the checkout
+    # on Windows, see TODO above COMPILER_RT_DIR.
+    asan_rt_lib_src_dir = os.path.join(COMPILER_RT_BUILD_DIR, 'lib', 'clang',
+                                       VERSION, 'lib', platform)
+  asan_rt_lib_dst_dir = os.path.join(LLVM_BUILD_DIR, 'lib', 'clang',
+                                     VERSION, 'lib', platform)
+  # Blacklists:
+  CopyDirectoryContents(os.path.join(asan_rt_lib_src_dir, '..', '..'),
+                        os.path.join(asan_rt_lib_dst_dir, '..', '..'),
+                        r'^.*blacklist\.txt$')
+  # Headers:
+  if sys.platform != 'win32':
+    CopyDirectoryContents(
+        os.path.join(COMPILER_RT_BUILD_DIR, 'include/sanitizer'),
+        os.path.join(LLVM_BUILD_DIR, 'lib/clang', VERSION, 'include/sanitizer'))
+  # Static and dynamic libraries:
+  CopyDirectoryContents(asan_rt_lib_src_dir, asan_rt_lib_dst_dir)
+  if sys.platform == 'darwin':
+    for dylib in glob.glob(os.path.join(asan_rt_lib_dst_dir, '*.dylib')):
+      # Fix LC_ID_DYLIB for the ASan dynamic libraries to be relative to
+      # @executable_path.
+      # TODO(glider): this is transitional. We'll need to fix the dylib
+      # name either in our build system, or in Clang. See also
+      # http://crbug.com/344836.
+      subprocess.call(['install_name_tool', '-id',
+                       '@executable_path/' + os.path.basename(dylib), dylib])
+
+
+  if sys.platform == 'win32':
+    # Make an extra copy of the sanitizer headers, to be put on the include path
+    # of the fallback compiler.
+    sanitizer_include_dir = os.path.join(LLVM_BUILD_DIR, 'lib', 'clang',
+                                         VERSION, 'include', 'sanitizer')
+    aux_sanitizer_include_dir = os.path.join(LLVM_BUILD_DIR, 'lib', 'clang',
+                                             VERSION, 'include_sanitizer',
+                                             'sanitizer')
+    EnsureDirExists(aux_sanitizer_include_dir)
+    for _, _, files in os.walk(sanitizer_include_dir):
+      for f in files:
+        CopyFile(os.path.join(sanitizer_include_dir, f),
+                 aux_sanitizer_include_dir)
+
+  if args.with_android:
+    make_toolchain = os.path.join(
+        ANDROID_NDK_DIR, 'build', 'tools', 'make_standalone_toolchain.py')
+    for target_arch in ['aarch64', 'arm', 'i686']:
+      # Make standalone Android toolchain for target_arch.
+      toolchain_dir = os.path.join(
+          LLVM_BUILD_DIR, 'android-toolchain-' + target_arch)
+      RunCommand([
+          make_toolchain,
+          '--api=' + ('21' if target_arch == 'aarch64' else '19'),
+          '--force',
+          '--install-dir=%s' % toolchain_dir,
+          '--stl=stlport',
+          '--arch=' + {
+              'aarch64': 'arm64',
+              'arm': 'arm',
+              'i686': 'x86',
+          }[target_arch]])
+      # Android NDK r9d copies a broken unwind.h into the toolchain, see
+      # http://crbug.com/357890
+      for f in glob.glob(os.path.join(toolchain_dir, 'include/c++/*/unwind.h')):
+        os.remove(f)
+
+      # Build ASan runtime for Android in a separate build tree.
+      build_dir = os.path.join(LLVM_BUILD_DIR, 'android-' + target_arch)
+      if not os.path.exists(build_dir):
+        os.mkdir(os.path.join(build_dir))
+      os.chdir(build_dir)
+      cflags = ['--target=%s-linux-androideabi' % target_arch,
+                '--sysroot=%s/sysroot' % toolchain_dir,
+                '-B%s' % toolchain_dir]
+      android_args = base_cmake_args + [
+        '-DCMAKE_C_COMPILER=' + os.path.join(LLVM_BUILD_DIR, 'bin/clang'),
+        '-DCMAKE_CXX_COMPILER=' + os.path.join(LLVM_BUILD_DIR, 'bin/clang++'),
+        '-DLLVM_CONFIG_PATH=' + os.path.join(LLVM_BUILD_DIR, 'bin/llvm-config'),
+        '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
+        '-DCMAKE_CXX_FLAGS=' + ' '.join(cflags),
+        '-DANDROID=1']
+      RmCmakeCache('.')
+      RunCommand(['cmake'] + android_args + [COMPILER_RT_DIR])
+      RunCommand(['ninja', 'libclang_rt.asan-%s-android.so' % target_arch])
+
+      # And copy it into the main build tree.
+      runtime = 'libclang_rt.asan-%s-android.so' % target_arch
+      for root, _, files in os.walk(build_dir):
+        if runtime in files:
+          shutil.copy(os.path.join(root, runtime), asan_rt_lib_dst_dir)
+
+  # Run tests.
+  if args.run_tests or use_head_revision:
+    os.chdir(LLVM_BUILD_DIR)
+    RunCommand(['ninja', 'cr-check-all'], msvc_arch='x64')
+  if args.run_tests:
+    if sys.platform == 'win32':
+      CopyDiaDllTo(os.path.join(LLVM_BUILD_DIR, 'bin'))
+    os.chdir(LLVM_BUILD_DIR)
+    RunCommand(['ninja', 'check-all'], msvc_arch='x64')
+
+  WriteStampFile(PACKAGE_VERSION)
+  print 'Clang update was successful.'
+  return 0
+
+
+def main():
+  parser = argparse.ArgumentParser(description='Build Clang.')
+  parser.add_argument('--bootstrap', action='store_true',
+                      help='first build clang with CC, then with itself.')
+  parser.add_argument('--if-needed', action='store_true',
+                      help="run only if the script thinks clang is needed")
+  parser.add_argument('--force-local-build', action='store_true',
+                      help="don't try to download prebuild binaries")
+  parser.add_argument('--gcc-toolchain', help='set the version for which gcc '
+                      'version be used for building; --gcc-toolchain=/opt/foo '
+                      'picks /opt/foo/bin/gcc')
+  parser.add_argument('--lto-gold-plugin', action='store_true',
+                      help='build LLVM Gold plugin with LTO')
+  parser.add_argument('--llvm-force-head-revision', action='store_true',
+                      help=('use the revision in the repo when printing '
+                            'the revision'))
+  parser.add_argument('--print-revision', action='store_true',
+                      help='print current clang revision and exit.')
+  parser.add_argument('--print-clang-version', action='store_true',
+                      help='print current clang version (e.g. x.y.z) and exit.')
+  parser.add_argument('--run-tests', action='store_true',
+                      help='run tests after building; only for local builds')
+  parser.add_argument('--tools', nargs='*',
+                      help='select which chrome tools to build',
+                      default=['plugins', 'blink_gc_plugin'])
+  parser.add_argument('--without-android', action='store_false',
+                      help='don\'t build Android ASan runtime (linux only)',
+                      dest='with_android',
+                      default=sys.platform.startswith('linux'))
+  args = parser.parse_args()
+
+  if args.lto_gold_plugin and not args.bootstrap:
+    print '--lto-gold-plugin requires --bootstrap'
+    return 1
+  if args.lto_gold_plugin and not sys.platform.startswith('linux'):
+    print '--lto-gold-plugin is only effective on Linux. Ignoring the option.'
+    args.lto_gold_plugin = False
+
+  if args.if_needed:
+    is_clang_required = False
+    # clang is always used on Mac and Linux.
+    if sys.platform == 'darwin' or sys.platform.startswith('linux'):
+      is_clang_required = True
+    # clang requested via $GYP_DEFINES.
+    if re.search(r'\b(clang|asan|lsan|msan|tsan)=1',
+                 os.environ.get('GYP_DEFINES', '')):
+      is_clang_required = True
+    # clang previously downloaded, keep it up to date.
+    # If you don't want this, delete third_party/llvm-build on your machine.
+    if os.path.isdir(LLVM_BUILD_DIR):
+      is_clang_required = True
+    if not is_clang_required:
+      return 0
+    if re.search(r'\b(make_clang_dir)=', os.environ.get('GYP_DEFINES', '')):
+      print 'Skipping Clang update (make_clang_dir= was set in GYP_DEFINES).'
+      return 0
+
+  global CLANG_REVISION, PACKAGE_VERSION
+  if args.print_revision:
+    if use_head_revision or args.llvm_force_head_revision:
+      print GetSvnRevision(LLVM_DIR)
+    else:
+      print PACKAGE_VERSION
+    return 0
+
+  if args.print_clang_version:
+    sys.stdout.write(VERSION)
+    return 0
+
+  # Don't buffer stdout, so that print statements are immediately flushed.
+  # Do this only after --print-revision has been handled, else we'll get
+  # an error message when this script is run from gn for some reason.
+  sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
+
+  if use_head_revision:
+    # Use a real revision number rather than HEAD to make sure that the stamp
+    # file logic works.
+    CLANG_REVISION = GetSvnRevision(LLVM_REPO_URL)
+    PACKAGE_VERSION = CLANG_REVISION + '-0'
+
+    args.force_local_build = True
+    if 'OS=android' not in os.environ.get('GYP_DEFINES', ''):
+      # Only build the Android ASan rt on ToT bots when targetting Android.
+      args.with_android = False
+
+  return UpdateClang(args)
+
+
+if __name__ == '__main__':
+  sys.exit(main())