Roll buildtools and clang for 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
index 55b64eeffa9bfd261e97f8d551eb8036efabf203..100bdec5cc88dd60957affff4f16c1ffb2d6eda4 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -3,12 +3,12 @@
 # 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."""
+"""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 contextlib
-import cStringIO
+import distutils.spawn
 import glob
 import os
 import pipes
@@ -18,26 +18,25 @@ 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://code.google.com/p/chromium/wiki/UpdatingClang
+# https://chromium.googlesource.com/chromium/src/+/master/docs/updating_clang.md
 # 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'
+CLANG_REVISION = '282487'
 
 use_head_revision = 'LLVM_FORCE_HEAD_REVISION' in os.environ
 if use_head_revision:
-  LLVM_WIN_REVISION = 'HEAD'
+  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" % (LLVM_WIN_REVISION, CLANG_SUB_REVISION)
+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__))
@@ -47,71 +46,135 @@ 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, '32bit-compiler-rt')
+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_DIR = os.path.join(LLVM_DIR, 'projects', 'compiler-rt')
+# 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.join(LLVM_DIR, '..', 'llvm-build', 'cr_build_revision')
+STAMP_FILE = os.path.normpath(
+    os.path.join(LLVM_DIR, '..', 'llvm-build', 'cr_build_revision'))
 BINUTILS_DIR = os.path.join(THIRD_PARTY_DIR, 'binutils')
-VERSION = '3.8.0'
+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 = 'https://commondatastorage.googleapis.com/chromium-browser-clang'
+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
-  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
+  num_retries = 3
+  retry_wait_s = 5  # Doubled at each retry.
+
   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():
+    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(STAMP_FILE, 'r') as f:
-      return f.read()
+    with open(path, 'r') as f:
+      return f.read().rstrip()
   except IOError:
     return ''
 
 
-def WriteStampFile(s):
+def WriteStampFile(s, path=STAMP_FILE):
   """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:
+  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)
@@ -129,6 +192,15 @@ def RmTree(dir):
   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
@@ -163,15 +235,15 @@ def RunCommand(command, msvc_arch=None, env=None, fail_hard=True):
 
 def CopyFile(src, dst):
   """Copy a file from src to dst."""
-  shutil.copy(src, 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."""
-  if not os.path.exists(dst):
-    os.makedirs(dst)
+  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):
@@ -181,9 +253,9 @@ def CopyDirectoryContents(src, dst, filename_filter=None):
 
 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)
+  print "Checking out %s r%s into '%s'" % (name, CLANG_REVISION, dir)
 
-  command = ['svn', 'checkout', '--force', url + '@' + LLVM_WIN_REVISION, dir]
+  command = ['svn', 'checkout', '--force', url + '@' + CLANG_REVISION, dir]
   if RunCommand(command, fail_hard=False):
     return
 
@@ -195,120 +267,9 @@ def Checkout(name, url, dir):
   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():
+  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)
 
 
@@ -337,30 +298,53 @@ def CreateChromeToolsShim():
     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-3.2.2-win32-x86.zip'
+    zip_name = 'cmake-3.4.3-win32-x86.zip'
     cmake_dir = os.path.join(LLVM_BUILD_TOOLS_DIR,
-                             'cmake-3.2.2-win32-x86', 'bin')
+                             'cmake-3.4.3-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')
+    zip_name = 'cmake343_%s.tgz' % suffix
+    cmake_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'cmake343', '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)
+    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
@@ -377,99 +361,152 @@ def GetVSVersion():
   # 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')
+  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
-  if ReadStampFile() == PACKAGE_VERSION:
-    print 'Already up to date.'
-    return 0
+
+  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
-    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
-
+    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()
 
-  RevertPreviouslyPatchedFiles()
   DeleteChromeToolsShim()
 
   Checkout('LLVM', LLVM_REPO_URL + '/llvm/trunk', LLVM_DIR)
   Checkout('Clang', LLVM_REPO_URL + '/cfe/trunk', CLANG_DIR)
-  if sys.platform == 'win32':
+  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)
-    # 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()
+    # 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
-  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'
+  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'
-    if not os.path.exists(LLVM_BOOTSTRAP_DIR):
-      os.makedirs(LLVM_BOOTSTRAP_DIR)
+    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),
@@ -477,11 +514,18 @@ def UpdateClang(args):
         ]
     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')
@@ -493,61 +537,78 @@ def UpdateClang(args):
     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'
 
-  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 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.
-  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.
+  # 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']
@@ -559,7 +620,13 @@ def UpdateClang(args):
     deployment_env = os.environ.copy()
     deployment_env['MACOSX_DEPLOYMENT_TARGET'] = deployment_target
 
-  cmake_args = base_cmake_args + [
+  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),
@@ -567,19 +634,26 @@ def UpdateClang(args):
       '-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)]
-  # 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)
+  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:
@@ -587,17 +661,21 @@ def UpdateClang(args):
     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.
+  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.
-  if not os.path.exists(COMPILER_RT_BUILD_DIR):
-    os.makedirs(COMPILER_RT_BUILD_DIR)
+  # 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).
@@ -608,13 +686,21 @@ def UpdateClang(args):
   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')]
-  RunCommand(['cmake'] + compiler_rt_args + [LLVM_DIR],
-              msvc_arch='x86', env=deployment_env)
+                         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':
@@ -624,17 +710,35 @@ def UpdateClang(args):
   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_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)
-  CopyDirectoryContents(asan_rt_lib_src_dir, asan_rt_lib_dst_dir,
-                        r'^.*-i386\.lib$')
-  CopyDirectoryContents(asan_rt_lib_src_dir, asan_rt_lib_dst_dir,
-                        r'^.*-i386\.dll$')
+  # 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])
 
-  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
@@ -644,22 +748,69 @@ def UpdateClang(args):
     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)
+    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(GetVSVersion().SetupScript('x64') +
-               ['&&', 'ninja', 'cr-check-all'])
+    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(GetVSVersion().SetupScript('x64') +
-               ['&&', 'ninja', 'check-all'])
+    RunCommand(['ninja', 'check-all'], msvc_arch='x64')
 
   WriteStampFile(PACKAGE_VERSION)
   print 'Clang update was successful.'
@@ -667,31 +818,6 @@ def UpdateClang(args):
 
 
 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.')
@@ -699,6 +825,14 @@ def main():
                       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',
@@ -708,16 +842,19 @@ def main():
   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')
-
+  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.
@@ -727,7 +864,7 @@ def main():
     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.
+    # 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
@@ -737,9 +874,9 @@ def main():
       print 'Skipping Clang update (make_clang_dir= was set in GYP_DEFINES).'
       return 0
 
-  global LLVM_WIN_REVISION, PACKAGE_VERSION
+  global CLANG_REVISION, PACKAGE_VERSION
   if args.print_revision:
-    if use_head_revision:
+    if use_head_revision or args.llvm_force_head_revision:
       print GetSvnRevision(LLVM_DIR)
     else:
       print PACKAGE_VERSION
@@ -757,12 +894,13 @@ def main():
   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'
+    CLANG_REVISION = GetSvnRevision(LLVM_REPO_URL)
+    PACKAGE_VERSION = CLANG_REVISION + '-0'
 
     args.force_local_build = True
-    # Skip local patches when using HEAD: they probably don't apply anymore.
-    args.with_patches = False
+    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)