binutils: Embed a relative path to the LLVM lib directory in binaries' rpaths.

third_party/binutils/build-one.sh

 #!/bin/sh
 # Copyright 2014 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 build binutils found in /build/binutils-XXXX when inside a chroot.
 # Don't call this script yourself, instead use the build-all.sh script.
 
 set -e
 
 if [ -z "$1" ]; then
  echo "Directory of binutils not given."
  exit 1
 fi
 
 cd "$1"
+
+# Ask the dynamic loader to load libstdc++ from the LLVM build directory if
+# available. That copy of libstdc++ is required by the gold plugin in the same
+# directory. The dynamic loader expects the relative path to start with $ORIGIN,
+# but because of escaping issues
+# (https://sourceware.org/ml/binutils/2009-05/msg00252.html)
+# we embed a dummy path with $ replaced with z and fix it up later.
+export LDFLAGS='-Wl,-rpath,zORIGIN/../../../../llvm-build/Release+Asserts/lib'
+
 ./configure --enable-gold=default --enable-threads --enable-plugins \
   --prefix=/build/output
 make -j8 all
 make install
+
+# Fix up zORIGIN -> $ORIGIN.
+bins="`echo /build/output/*/bin/*`"

[krasin, 2015/09/02 03:09:53]

I believe that generally "$(echo /build/output/*/bin/*)" is the preferable
syntax in bash, since it allows nesting. Here, it's probably find to keep as is.

[pcc, 2015/09/05 03:10:06]

Done.

+sed -i.orig 's,zORIGIN/\.\.,$ORIGIN/..,g' $bins

[krasin, 2015/09/02 03:09:53]

1) why do we need this trick with echo?

[pcc, 2015/09/05 03:10:06]

The sed -i command will leave .orig files behind. We don't want them to appear
in the for loop below. Added comment clarifying.

+

[krasin, 2015/09/02 03:09:53]

2) can you please explain how did you chose the sed command?

why isn't it just 's/zORIGIN/$ORIGIN/g'? Am I missing something?

[pcc, 2015/09/05 03:10:06]

Yes it can be that instead. I wrote the longer sed command before stumbling
across the trick for verifying the edit distance.

+# Verify that we changed only one byte per executable.
+for bin in $bins; do
+  test "`cmp -l $bin.orig $bin | wc -l`" = 1

[krasin, 2015/09/02 03:09:54]

Can you please make this script to output some message in case, if this
comparison fails? Something that would hint that we need to chose a more
intricate placeholder than just zORIGIN.

That would save some time for the one who will have this script failed.

[pcc, 2015/09/05 03:10:06]

Done.

+done
+
+rm /build/output/*/bin/*.orig