Automatically download gold plugin for cfi builds.

build/download_gold_plugin.py

 #!/usr/bin/env python
 # Copyright 2015 the V8 project authors. All rights reserved.
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Script to download LLVM gold plugin from google storage."""
 
 import json
 import os
+import re
 import shutil
 import subprocess
 import sys
 import zipfile
 
 SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
 CHROME_SRC = os.path.abspath(os.path.join(SCRIPT_DIR, os.pardir))
 sys.path.insert(0, os.path.join(CHROME_SRC, 'tools'))
 
 import find_depot_tools
 
 DEPOT_PATH = find_depot_tools.add_depot_tools_to_path()
 GSUTIL_PATH = os.path.join(DEPOT_PATH, 'gsutil.py')
 
 LLVM_BUILD_PATH = os.path.join(CHROME_SRC, 'third_party', 'llvm-build',
                                'Release+Asserts')
 CLANG_UPDATE_PY = os.path.join(CHROME_SRC, 'tools', 'clang', 'scripts',
                                'update.py')
 CLANG_REVISION = os.popen(CLANG_UPDATE_PY + ' --print-revision').read().rstrip()
 
 CLANG_BUCKET = 'gs://chromium-browser-clang/Linux_x64'
 
+GOLD_PLUGIN_PATH = os.path.join(LLVM_BUILD_PATH, 'lib', 'LLVMgold.so')
+
+sys.path.insert(0, os.path.join(CHROME_SRC, 'tools', 'clang', 'scripts'))
+
+import update
+
 def main():
+  if not re.search(r'cfi_vptr=1', os.environ.get('GYP_DEFINES', '')):
+    # Bailout if this is not a cfi build.
+    print 'Skipping gold plugin download for non-cfi build.'
+    return 0
+  if (os.path.exists(GOLD_PLUGIN_PATH) and
+      update.ReadStampFile().strip() == update.PACKAGE_VERSION):
+    # Bailout if clang is up-to-date. This requires the script to be run before
+    # the clang update step! I.e. afterwards clang would always be up-to-date.
+    print 'Skipping gold plugin download. File present and clang up to date.'
+    return 0
+
   targz_name = 'llvmgold-%s.tgz' % CLANG_REVISION
   remote_path = '%s/%s' % (CLANG_BUCKET, targz_name)
 
   os.chdir(LLVM_BUILD_PATH)
 
   # TODO(pcc): Fix gsutil.py cp url file < /dev/null 2>&0
   # (currently aborts with exit code 1,
   # https://github.com/GoogleCloudPlatform/gsutil/issues/289) or change the
   # stdin->stderr redirect in update.py to do something else (crbug.com/494442).
   subprocess.check_call(['python', GSUTIL_PATH,
                          'cp', remote_path, targz_name],
                         stderr=open('/dev/null', 'w'))
   subprocess.check_call(['tar', 'xzf', targz_name])
   os.remove(targz_name)
   return 0
 
 if __name__ == '__main__':
   sys.exit(main())