[build] Always keep gold plugin in sync with clang version

The old logic made the cfi build fail on each clang update.

Bug: chromium:726584
Change-Id: Ia24181d3bc92eb18116c2ac2b42ac2c68f02ce25
Reviewed-on: https://chromium-review.googlesource.com/518185Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45601}

.gitignore

@@ -36,6 +36,7 @@
 /base
 /build
 /buildtools
+/gypfiles/.gold_plugin
 /gypfiles/win_toolchain.json
 /hydrogen.cfg
 /obj

DEPS

@@ -262,13 +262,6 @@ hooks = [
         'v8/third_party/binutils/download.py',
     ],
   },
-  {
-    # Pull gold plugin if needed or requested via GYP_DEFINES.
-    # Note: This must run before the clang update.
-    'name': 'gold_plugin',
-    'pattern': '.',
-    'action': ['python', 'v8/gypfiles/download_gold_plugin.py'],
-  },
   {
     # Pull clang if needed or requested via GYP_DEFINES.
     # Note: On Win, this should run after win_toolchain, as it may use it.
@@ -276,6 +269,12 @@ hooks = [
     'pattern': '.',
     'action': ['python', 'v8/tools/clang/scripts/update.py', '--if-needed'],
   },
+  {
+    # Pull gold plugin if needed or requested via GYP_DEFINES.
+    'name': 'gold_plugin',
+    'pattern': '.',
+    'action': ['python', 'v8/gypfiles/download_gold_plugin.py'],
+  },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",

gypfiles/download_gold_plugin.py

@@ -41,25 +41,25 @@ 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
+GOLD_PLUGIN_VERSION_FILE = os.path.join(CHROME_SRC, 'gypfiles', '.gold_plugin')
 
 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.'
+  previous_version = ''
+  if os.path.exists(GOLD_PLUGIN_VERSION_FILE):
+    with open(GOLD_PLUGIN_VERSION_FILE) as f:
+      previous_version = f.read().strip()
+  if (os.path.exists(GOLD_PLUGIN_PATH) and previous_version == CLANG_REVISION):
+    # Bailout if gold plugin is up-to-date. This requires the script to be run
+    # after the clang update step.
+    print 'Skipping gold plugin download (up to date).'
     return 0
 
-  # Make sure this works on empty checkouts (i.e. clang not downloaded yet).
-  if not os.path.exists(LLVM_BUILD_PATH):
-    os.makedirs(LLVM_BUILD_PATH)
+  # Make sure clang has been downloaded already.
+  assert os.path.exists(LLVM_BUILD_PATH)
 
   targz_name = 'llvmgold-%s.tgz' % CLANG_REVISION
   remote_path = '%s/%s' % (CLANG_BUCKET, targz_name)
@@ -75,6 +75,9 @@ def main():
                         stderr=open('/dev/null', 'w'))
   subprocess.check_call(['tar', 'xzf', targz_name])
   os.remove(targz_name)
+
+  with open(GOLD_PLUGIN_VERSION_FILE, 'w') as f:
+    f.write(CLANG_REVISION)
   return 0
 
 if __name__ == '__main__':