[Bug gold/16388] New: Linking with Gold causes threading strange threading issues

[jpakkane at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16388

            Bug ID: 16388
           Summary: Linking with Gold causes threading strange threading
                    issues
           Product: binutils
           Version: 2.24
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gold
          Assignee: ian at airs dot com
          Reporter: jpakkane at gmail dot com
                CC: ccoutant at google dot com

We have discovered an issue where linking with Gold (on x86-64 without using
lto or any other fancy machinery) causes problems in multithreaded code. More
specifically code that functions perfectly with bfd hangs, freezes or segfaults
when linked with Gold. We have not been able to reduce this to a simple test
case but this is how to replicate the issue.

First you need to install the dependency, which is Unity-api
(https://launchpad.net/unity-api). This is available in Ubuntu 14/04
development version (and possibly 13/10). Otherwise you need to compile from
source.

Then do this to compile and test the regular bfd version:

bzr branch lp:unity-scopes-api (current trunk rev is 114)
cd unity-scopes-api
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=debug ..
make
test/gtest/scopes/internal/Reaper/Reaper_test

This works reliably. Then do a Gold build:

<cd into source root>
mkdir buildgold
cd buildgold
LDFLAGS=-fuse-ld=gold cmake -DCMAKE_BUILD_TYPE=debug ..
make
test/gtest/scopes/internal/Reaper/Reaper_test

This almost always hangs or sometimes segfaults.

It may well be that our code has a bug and Gold only makes it surface. However
we have spent quite a lot of time looking into our code and as far as we can
tell the code should not have bugs.

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