CFI: download LLVM Gold plugin, if requested by env var or GYP_DEFINES.

tools/clang/scripts/update.sh

Index: tools/clang/scripts/update.sh
diff --git a/tools/clang/scripts/update.sh b/tools/clang/scripts/update.sh
index 8195f990cdbee03dd9b7fa9500d1ae8fdf44f9f5..9a04e0a70bb21995423d41c3974dfa3940495635 100755
--- a/tools/clang/scripts/update.sh
+++ b/tools/clang/scripts/update.sh
@@ -53,6 +53,12 @@ if [[ -z "$LLVM_DOWNLOAD_GOLD_PLUGIN" ]]; then
   LLVM_DOWNLOAD_GOLD_PLUGIN=
 fi
 
+if [[ "$GYP_DEFINES" =~ .*cfi_vptr=1.* ]] || \

[hans, 2015/10/09 21:42:48]

Doesn't this still need to be guarded by "if Linux ..."?

[krasin, 2015/10/09 21:50:18]

Done.

+   [[ "$GYP_DEFINES" =~ .*buildtype=Official.* ]] || \
+   [[ "$GYP_DEFINES" =~ .*branding=Chrome.* ]] ; then

[Nico, 2015/10/09 21:40:10]

Let's do the same as
https://code.google.com/p/chromium/codesearch#chromium/src/build/linux/sysroo...
and only do this if the latter 2 are both true; drop the first

[krasin, 2015/10/09 21:50:18]

Done.

+  # LLVM Gold plugin is required to build with this configuration.
+  LLVM_DOWNLOAD_GOLD_PLUGIN=1
+fi
 
 # Die if any command dies, error on undefined variable expansions.
 set -eu
@@ -235,7 +241,10 @@ if [[ -f "${STAMP_FILE}" ]]; then
        [[ "${PREVIOUSLY_BUILT_REVISON}" = \
           "${PACKAGE_VERSION}" ]]; then
     echo "Clang already at ${PACKAGE_VERSION}"
-    exit 0
+    if [[ -z "${LLVM_DOWNLOAD_GOLD_PLUGIN}" ]] || \
+       [[ -f "${LLVM_BUILD_DIR}/lib/LLVMgold.so" ]]; then

[Nico, 2015/10/09 21:40:10]

with this setup it can theoretically happen that an old LLVMgold plugin happens
to be around. if that turns out to be a problem, I suppose we could have another
stamp file for the plugin, but I think this is fine as-is for nmow.

[krasin, 2015/10/09 21:50:18]

I raised this point, Hans correctly pointed out that we delete the whole
directory, if a new version of Clang is downloaded (including the plugin):
https://codereview.chromium.org/1373043003/#msg13

[Nico, 2015/10/09 21:52:37]

Smart guy, that Hans!

+      exit 0
+    fi
   fi
 fi
 # To always force a new build if someone interrupts their build half way.