Starting work on full GN build

tools/clang/scripts/update.py

Index: tools/clang/scripts/update.py
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
new file mode 100755
index 0000000000000000000000000000000000000000..55b64eeffa9bfd261e97f8d551eb8036efabf203
--- /dev/null
+++ b/tools/clang/scripts/update.py
@@ -0,0 +1,771 @@
+#!/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.
+
+"""Windows can't run .sh files, so this is a Python implementation of
+update.sh. This script should replace update.sh on all platforms eventually."""
+
+import argparse
+import contextlib
+import cStringIO
+import glob
+import os
+import pipes
+import re
+import shutil
+import subprocess
+import stat
+import sys
+import tarfile
+import time
+import urllib2
+import zipfile
+
+# Do NOT CHANGE this if you don't know what you're doing -- see
+# https://code.google.com/p/chromium/wiki/UpdatingClang
+# Reverting problematic clang rolls is safe, though.
+# Note: this revision is only used for Windows. Other platforms use update.sh.
+# TODO(thakis): Use the same revision on Windows and non-Windows.
+# TODO(thakis): Remove update.sh, use update.py everywhere.
+LLVM_WIN_REVISION = '242415'
+
+use_head_revision = 'LLVM_FORCE_HEAD_REVISION' in os.environ
+if use_head_revision:
+  LLVM_WIN_REVISION = 'HEAD'
+
+# This is incremented when pushing a new build of Clang at the same revision.
+CLANG_SUB_REVISION=1
+
+PACKAGE_VERSION = "%s-%s" % (LLVM_WIN_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')
+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, '32bit-compiler-rt')
+CLANG_DIR = os.path.join(LLVM_DIR, 'tools', 'clang')
+LLD_DIR = os.path.join(LLVM_DIR, 'tools', 'lld')
+COMPILER_RT_DIR = os.path.join(LLVM_DIR, 'projects', '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.join(LLVM_DIR, '..', 'llvm-build', 'cr_build_revision')
+BINUTILS_DIR = os.path.join(THIRD_PARTY_DIR, 'binutils')
+VERSION = '3.8.0'
+
+# URL for pre-built binaries.
+CDS_URL = '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']
+
+
+def DownloadUrl(url, output_file):
+  """Download url into output_file."""
+  CHUNK_SIZE = 4096
+  TOTAL_DOTS = 10
+  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
+  print ' Done.'
+
+
+def ReadStampFile():
+  """Return the contents of the stamp file, or '' if it doesn't exist."""
+  try:
+    with open(STAMP_FILE, 'r') as f:
+      return f.read()
+  except IOError:
+    return ''
+
+
+def WriteStampFile(s):
+  """Write s to the stamp file."""
+  if not os.path.exists(os.path.dirname(STAMP_FILE)):
+    os.makedirs(os.path.dirname(STAMP_FILE))
+  with open(STAMP_FILE, 'w') as f:
+    f.write(s)
+
+
+def GetSvnRevision(svn_repo):
+  """Returns current revision of the svn repo at svn_repo."""
+  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 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."""
+  shutil.copy(src, dst)
+  print "Copying %s to %s" % (src, dst)
+
+
+def CopyDirectoryContents(src, dst, filename_filter=None):
+  """Copy the files from directory src to dst
+  with an optional filename filter."""
+  if not os.path.exists(dst):
+    os.makedirs(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, LLVM_WIN_REVISION, dir)
+
+  command = ['svn', 'checkout', '--force', url + '@' + LLVM_WIN_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 RevertPreviouslyPatchedFiles():
+  print 'Reverting previously patched files'
+  files = [
+    '%(clang)s/test/Index/crash-recovery-modules.m',
+    '%(clang)s/unittests/libclang/LibclangTest.cpp',
+    '%(compiler_rt)s/lib/asan/asan_rtl.cc',
+    '%(compiler_rt)s/test/asan/TestCases/Linux/new_array_cookie_test.cc',
+    '%(llvm)s/test/DebugInfo/gmlt.ll',
+    '%(llvm)s/lib/CodeGen/SpillPlacement.cpp',
+    '%(llvm)s/lib/CodeGen/SpillPlacement.h',
+    '%(llvm)s/lib/Transforms/Instrumentation/MemorySanitizer.cpp',
+    '%(clang)s/test/Driver/env.c',
+    '%(clang)s/lib/Frontend/InitPreprocessor.cpp',
+    '%(clang)s/test/Frontend/exceptions.c',
+    '%(clang)s/test/Preprocessor/predefined-exceptions.m',
+    '%(llvm)s/test/Bindings/Go/go.test',
+    '%(clang)s/lib/Parse/ParseExpr.cpp',
+    '%(clang)s/lib/Parse/ParseTemplate.cpp',
+    '%(clang)s/lib/Sema/SemaDeclCXX.cpp',
+    '%(clang)s/lib/Sema/SemaExprCXX.cpp',
+    '%(clang)s/test/SemaCXX/default2.cpp',
+    '%(clang)s/test/SemaCXX/typo-correction-delayed.cpp',
+    '%(compiler_rt)s/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc',
+    '%(compiler_rt)s/test/tsan/signal_segv_handler.cc',
+    '%(compiler_rt)s/lib/sanitizer_common/sanitizer_coverage_libcdep.cc',
+    '%(compiler_rt)s/cmake/config-ix.cmake',
+    '%(compiler_rt)s/CMakeLists.txt',
+    '%(compiler_rt)s/lib/ubsan/ubsan_platform.h',
+    ]
+  for f in files:
+    f = f % {
+        'clang': CLANG_DIR,
+        'compiler_rt': COMPILER_RT_DIR,
+        'llvm': LLVM_DIR,
+        }
+    if os.path.exists(f):
+      os.remove(f)  # For unversioned files.
+      RunCommand(['svn', 'revert', f])
+
+
+def ApplyLocalPatches():
+  # There's no patch program on Windows by default.  We don't need patches on
+  # Windows yet, and maybe this not working on Windows will motivate us to
+  # remove patches over time.
+  assert sys.platform != 'win32'
+
+  # Apply patch for tests failing with --disable-pthreads (llvm.org/PR11974)
+  clang_patches = [ r"""\
+--- test/Index/crash-recovery-modules.m	(revision 202554)
++++ test/Index/crash-recovery-modules.m	(working copy)
+@@ -12,6 +12,8 @@
+ 
+ // REQUIRES: crash-recovery
+ // REQUIRES: shell
++// XFAIL: *
++//    (PR11974)
+ 
+ @import Crash;
+""", r"""\
+--- unittests/libclang/LibclangTest.cpp (revision 215949)
++++ unittests/libclang/LibclangTest.cpp (working copy)
+@@ -431,7 +431,7 @@
+   EXPECT_EQ(0U, clang_getNumDiagnostics(ClangTU));
+ }
+
+-TEST_F(LibclangReparseTest, ReparseWithModule) {
++TEST_F(LibclangReparseTest, DISABLED_ReparseWithModule) {
+   const char *HeaderTop = "#ifndef H\n#define H\nstruct Foo { int bar;";
+   const char *HeaderBottom = "\n};\n#endif\n";
+   const char *MFile = "#include \"HeaderFile.h\"\nint main() {"
+"""
+      ]
+
+  # This Go bindings test doesn't work after bootstrap on Linux, PR21552.
+  llvm_patches = [ r"""\
+--- test/Bindings/Go/go.test    (revision 223109)
++++ test/Bindings/Go/go.test    (working copy)
+@@ -1,3 +1,3 @@
+-; RUN: llvm-go test llvm.org/llvm/bindings/go/llvm
++; RUN: true
+ 
+ ; REQUIRES: shell
+"""
+      ]
+
+  # The UBSan run-time, which is now bundled with the ASan run-time, doesn't
+  # work on Mac OS X 10.8 (PR23539).
+  compiler_rt_patches = [ r"""\
+--- CMakeLists.txt	(revision 241602)
++++ CMakeLists.txt	(working copy)
+@@ -305,6 +305,7 @@
+       list(APPEND SANITIZER_COMMON_SUPPORTED_OS iossim)
+     endif()
+   endif()
++  set(SANITIZER_MIN_OSX_VERSION "10.7")
+   if(SANITIZER_MIN_OSX_VERSION VERSION_LESS "10.7")
+     message(FATAL_ERROR "Too old OS X version: ${SANITIZER_MIN_OSX_VERSION}")
+   endif()
+"""
+      ]
+
+  for path, patches in [(LLVM_DIR, llvm_patches),
+                        (CLANG_DIR, clang_patches),
+                        (COMPILER_RT_DIR, compiler_rt_patches)]:
+    print 'Applying patches in', path
+    for patch in patches:
+      print patch
+      p = subprocess.Popen( ['patch', '-p0', '-d', path], stdin=subprocess.PIPE)
+      (stdout, stderr) = p.communicate(input=patch)
+      if p.returncode != 0:
+        raise RuntimeError('stdout %s, stderr %s' % (stdout, stderr))
+
+
+def DeleteChromeToolsShim():
+  shutil.rmtree(CHROME_TOOLS_SHIM_DIR, ignore_errors=True)
+
+
+def CreateChromeToolsShim():
+  """Hooks the Chrome tools into the LLVM build.
+
+  Several Chrome tools have dependencies on LLVM/Clang libraries. The LLVM build
+  detects implicit tools in the tools subdirectory, so this helper install a
+  shim CMakeLists.txt that forwards to the real directory for the Chrome tools.
+
+  Note that the shim directory name intentionally has no - or _. The implicit
+  tool detection logic munges them in a weird way."""
+  assert not any(i in os.path.basename(CHROME_TOOLS_SHIM_DIR) for i in '-_')
+  os.mkdir(CHROME_TOOLS_SHIM_DIR)
+  with file(os.path.join(CHROME_TOOLS_SHIM_DIR, 'CMakeLists.txt'), 'w') as f:
+    f.write('# Automatically generated by tools/clang/scripts/update.py. ' +
+            'Do not edit.\n')
+    f.write('# Since tools/clang is located in another directory, use the \n')
+    f.write('# two arg version to specify where build artifacts go. CMake\n')
+    f.write('# disallows reuse of the same binary dir for multiple source\n')
+    f.write('# dirs, so the build artifacts need to go into a subdirectory.\n')
+    f.write('# dirs, so the build artifacts need to go into a subdirectory.\n')
+    f.write('if (CHROMIUM_TOOLS_SRC)\n')
+    f.write('  add_subdirectory(${CHROMIUM_TOOLS_SRC} ' +
+              '${CMAKE_CURRENT_BINARY_DIR}/a)\n')
+    f.write('endif (CHROMIUM_TOOLS_SRC)\n')
+
+
+def AddCMakeToPath():
+  """Download CMake and add it to PATH."""
+  if sys.platform == 'win32':
+    zip_name = 'cmake-3.2.2-win32-x86.zip'
+    cmake_dir = os.path.join(LLVM_BUILD_TOOLS_DIR,
+                             'cmake-3.2.2-win32-x86', 'bin')
+  else:
+    suffix = 'Darwin' if sys.platform == 'darwin' else 'Linux'
+    zip_name = 'cmake310_%s.tgz' % suffix
+    cmake_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'cmake310', 'bin')
+  if not os.path.exists(cmake_dir):
+    if not os.path.exists(LLVM_BUILD_TOOLS_DIR):
+      os.makedirs(LLVM_BUILD_TOOLS_DIR)
+    # The cmake archive is smaller than 20 MB, small enough to keep in memory:
+    with contextlib.closing(cStringIO.StringIO()) as f:
+      DownloadUrl(CDS_URL + '/tools/' + zip_name, f)
+      f.seek(0)
+      if zip_name.endswith('.zip'):
+        zipfile.ZipFile(f).extractall(path=LLVM_BUILD_TOOLS_DIR)
+      else:
+        tarfile.open(mode='r:gz', fileobj=f).extractall(path=
+            LLVM_BUILD_TOOLS_DIR)
+  os.environ['PATH'] = cmake_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('2013')
+  return vs_version
+
+
+def UpdateClang(args):
+  print 'Updating Clang to %s...' % PACKAGE_VERSION
+  if ReadStampFile() == PACKAGE_VERSION:
+    print 'Already up to date.'
+    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
+    cds_full_url = CDS_URL + '/Win/' + cds_file
+
+    # Check if there's a prebuilt binary and if so just fetch that. That's
+    # faster, and goma relies on having matching binary hashes on client and
+    # server too.
+    print 'Trying to download prebuilt clang'
+
+    # clang packages are smaller than 50 MB, small enough to keep in memory.
+    with contextlib.closing(cStringIO.StringIO()) as f:
+      try:
+        DownloadUrl(cds_full_url, f)
+        f.seek(0)
+        tarfile.open(mode='r:gz', fileobj=f).extractall(path=LLVM_BUILD_DIR)
+        print 'clang %s unpacked' % PACKAGE_VERSION
+        # Download the gold plugin if requested to by an environment variable.
+        # This is used by the CFI ClusterFuzz bot.
+        if 'LLVM_DOWNLOAD_GOLD_PLUGIN' in os.environ:
+          RunCommand(['python', CHROMIUM_DIR+'/build/download_gold_plugin.py'])
+        WriteStampFile(PACKAGE_VERSION)
+        return 0
+      except urllib2.HTTPError:
+        print 'Did not find prebuilt clang %s, building locally' % cds_file
+
+  AddCMakeToPath()
+
+  RevertPreviouslyPatchedFiles()
+  DeleteChromeToolsShim()
+
+  Checkout('LLVM', LLVM_REPO_URL + '/llvm/trunk', LLVM_DIR)
+  Checkout('Clang', LLVM_REPO_URL + '/cfe/trunk', CLANG_DIR)
+  if sys.platform == 'win32':
+    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)
+    # While we're bundling our own libc++ on OS X, we need to compile libc++abi
+    # into it too (since OS X 10.6 doesn't have libc++abi.dylib either).
+    Checkout('libcxxabi', LLVM_REPO_URL + '/libcxxabi/trunk', LIBCXXABI_DIR)
+
+  if args.with_patches and sys.platform != 'win32':
+    ApplyLocalPatches()
+
+  cc, cxx = None, None
+  cflags = cxxflags = ldflags = []
+
+  # 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.
+  # TODO(thakis): Some bots are still on 10.6 (nacl...), so for now bundle
+  # libc++.dylib.  Remove this once all bots are on 10.7+, then use
+  # -DLLVM_ENABLE_LIBCXX=ON and change deployment_target to 10.7.
+  deployment_target = ''
+
+  if sys.platform == 'darwin':
+    # 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++', '-nostdinc++',
+                '-I' + os.path.join(LIBCXX_DIR, 'include')] + cflags
+    if args.bootstrap:
+      deployment_target = '10.6'
+
+  base_cmake_args = ['-GNinja',
+                     '-DCMAKE_BUILD_TYPE=Release',
+                     '-DLLVM_ENABLE_ASSERTIONS=ON',
+                     '-DLLVM_ENABLE_THREADS=OFF',
+                     ]
+
+  if args.bootstrap:
+    print 'Building bootstrap compiler'
+    if not os.path.exists(LLVM_BOOTSTRAP_DIR):
+      os.makedirs(LLVM_BOOTSTRAP_DIR)
+    os.chdir(LLVM_BOOTSTRAP_DIR)
+    bootstrap_args = base_cmake_args + [
+        '-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)
+    RunCommand(['cmake'] + bootstrap_args + [LLVM_DIR], msvc_arch='x64')
+    RunCommand(['ninja'], msvc_arch='x64')
+    if args.run_tests:
+      RunCommand(['ninja', 'check-all'], msvc_arch='x64')
+    RunCommand(['ninja', 'install'], msvc_arch='x64')
+
+    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++')
+    print 'Building final compiler'
+
+  if sys.platform == 'darwin':
+    # Build libc++.dylib while some bots are still on OS X 10.6.
+    libcxxbuild = os.path.join(LLVM_BUILD_DIR, 'libcxxbuild')
+    if os.path.isdir(libcxxbuild):
+      RmTree(libcxxbuild)
+    libcxxflags = ['-O3', '-std=c++11', '-fstrict-aliasing']
+
+    # libcxx and libcxxabi both have a file stdexcept.cpp, so put their .o files
+    # into different subdirectories.
+    os.makedirs(os.path.join(libcxxbuild, 'libcxx'))
+    os.chdir(os.path.join(libcxxbuild, 'libcxx'))
+    RunCommand(['c++', '-c'] + cxxflags + libcxxflags +
+                glob.glob(os.path.join(LIBCXX_DIR, 'src', '*.cpp')))
+
+    os.makedirs(os.path.join(libcxxbuild, 'libcxxabi'))
+    os.chdir(os.path.join(libcxxbuild, 'libcxxabi'))
+    RunCommand(['c++', '-c'] + cxxflags + libcxxflags +
+               glob.glob(os.path.join(LIBCXXABI_DIR, 'src', '*.cpp')) +
+               ['-I' + os.path.join(LIBCXXABI_DIR, 'include')])
+
+    os.chdir(libcxxbuild)
+    libdir = os.path.join(LIBCXX_DIR, 'lib')
+    RunCommand(['cc'] + glob.glob('libcxx/*.o') + glob.glob('libcxxabi/*.o') +
+        ['-o', 'libc++.1.dylib', '-dynamiclib', '-nodefaultlibs',
+         '-current_version', '1', '-compatibility_version', '1', '-lSystem',
+         '-install_name', '@executable_path/libc++.dylib',
+         '-Wl,-unexported_symbols_list,' + libdir + '/libc++unexp.exp',
+         '-Wl,-force_symbols_not_weak_list,' + libdir + '/notweak.exp',
+         '-Wl,-force_symbols_weak_list,' + libdir + '/weak.exp'])
+    if os.path.exists('libc++.dylib'):
+      os.remove('libc++.dylib')
+    os.symlink('libc++.1.dylib', 'libc++.dylib')
+    ldflags += ['-stdlib=libc++', '-L' + libcxxbuild]
+
+    if args.bootstrap:
+      # Now that the libc++ headers have been installed and libc++.dylib is
+      # built, delete the libc++ checkout again so that it's not part of the
+      # main build below -- the libc++(abi) tests don't pass on OS X in
+      # bootstrap builds (http://llvm.org/PR24068)
+      RmTree(LIBCXX_DIR)
+      RmTree(LIBCXXABI_DIR)
+      cxxflags = ['-stdlib=libc++', '-nostdinc++',
+                  '-I' + os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR,
+                                      'include/c++/v1')
+                  ] + cflags
+
+  # Build clang.
+  binutils_incdir = ''
+  if sys.platform.startswith('linux'):
+    binutils_incdir = os.path.join(BINUTILS_DIR, 'Linux_x64/Release/include')
+
+  # If building at head, define a macro that plugins can use for #ifdefing
+  # out code that builds at head, but not at LLVM_WIN_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 = 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,
+      '-DCHROMIUM_TOOLS_SRC=%s' % os.path.join(CHROMIUM_DIR, 'tools', 'clang'),
+      '-DCHROMIUM_TOOLS=%s' % ';'.join(args.tools)]
+  # 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)
+
+  if not os.path.exists(LLVM_BUILD_DIR):
+    os.makedirs(LLVM_BUILD_DIR)
+  os.chdir(LLVM_BUILD_DIR)
+  RunCommand(['cmake'] + cmake_args + [LLVM_DIR],
+             msvc_arch='x64', env=deployment_env)
+  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':
+    CopyFile(os.path.join(LLVM_BUILD_DIR, 'libc++.1.dylib'),
+             os.path.join(LLVM_BUILD_DIR, 'bin'))
+    # 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')])
+
+  # Do an x86 build of compiler-rt to get the 32-bit ASan run-time.
+  # TODO(hans): Remove once the regular build above produces this.
+  if not os.path.exists(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 != 'win32':
+    compiler_rt_args += ['-DLLVM_CONFIG_PATH=' +
+                         os.path.join(LLVM_BUILD_DIR, 'bin', 'llvm-config')]
+  RunCommand(['cmake'] + compiler_rt_args + [LLVM_DIR],
+              msvc_arch='x86', env=deployment_env)
+  RunCommand(['ninja', 'compiler-rt'], msvc_arch='x86')
+
+  # 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', 'clang',
+                                     VERSION, 'lib', platform)
+  asan_rt_lib_dst_dir = os.path.join(LLVM_BUILD_DIR, 'lib', 'clang',
+                                     VERSION, 'lib', platform)
+  CopyDirectoryContents(asan_rt_lib_src_dir, asan_rt_lib_dst_dir,
+                        r'^.*-i386\.lib$')
+  CopyDirectoryContents(asan_rt_lib_src_dir, asan_rt_lib_dst_dir,
+                        r'^.*-i386\.dll$')
+
+  CopyFile(os.path.join(asan_rt_lib_src_dir, '..', '..', 'asan_blacklist.txt'),
+           os.path.join(asan_rt_lib_dst_dir, '..', '..'))
+
+  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')
+    if not os.path.exists(aux_sanitizer_include_dir):
+      os.makedirs(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)
+
+  # Run tests.
+  if args.run_tests or use_head_revision:
+    os.chdir(LLVM_BUILD_DIR)
+    RunCommand(GetVSVersion().SetupScript('x64') +
+               ['&&', 'ninja', 'cr-check-all'])
+  if args.run_tests:
+    os.chdir(LLVM_BUILD_DIR)
+    RunCommand(GetVSVersion().SetupScript('x64') +
+               ['&&', 'ninja', 'check-all'])
+
+  WriteStampFile(PACKAGE_VERSION)
+  print 'Clang update was successful.'
+  return 0
+
+
+def main():
+  if not sys.platform in ['win32', 'cygwin']:
+    # For non-Windows, fall back to update.sh.
+    # TODO(hans): Make update.py replace update.sh completely.
+
+    # This script is called by gclient. gclient opens its hooks subprocesses
+    # with (stdout=subprocess.PIPE, stderr=subprocess.STDOUT) and then does
+    # custom output processing that breaks printing '\r' characters for
+    # single-line updating status messages as printed by curl and wget.
+    # Work around this by setting stderr of the update.sh process to stdin (!):
+    # gclient doesn't redirect stdin, and while stdin itself is read-only, a
+    # dup()ed sys.stdin is writable, try
+    #   fd2 = os.dup(sys.stdin.fileno()); os.write(fd2, 'hi')
+    # TODO: Fix gclient instead, http://crbug.com/95350
+    if '--no-stdin-hack' in sys.argv:
+      sys.argv.remove('--no-stdin-hack')
+      stderr = None
+    else:
+      try:
+        stderr = os.fdopen(os.dup(sys.stdin.fileno()))
+      except:
+        stderr = sys.stderr
+    return subprocess.call(
+        [os.path.join(os.path.dirname(__file__), 'update.sh')] + sys.argv[1:],
+        stderr=stderr)
+
+  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('--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-patches', action='store_false',
+                      help="don't apply patches (default)", dest='with_patches',
+                      default=True)
+
+  # For now, these flags are only used for the non-Windows flow, but argparser
+  # gets mad if it sees a flag it doesn't recognize.
+  parser.add_argument('--no-stdin-hack', action='store_true')
+
+  args = parser.parse_args()
+
+  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 LLVM_WIN_REVISION, PACKAGE_VERSION
+  if args.print_revision:
+    if use_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.
+    LLVM_WIN_REVISION = GetSvnRevision(LLVM_REPO_URL)
+    PACKAGE_VERSION = LLVM_WIN_REVISION + '-0'
+
+    args.force_local_build = True
+    # Skip local patches when using HEAD: they probably don't apply anymore.
+    args.with_patches = False
+
+  return UpdateClang(args)
+
+
+if __name__ == '__main__':
+  sys.exit(main())