clang++ no longer ABI-compatible with g++

Bug #1510042 reported by Jeff Abrahamson on 2015-10-26
This bug affects 16 people
Affects Status Importance Assigned to Milestone
llvm-toolchain-3.8 (Debian)
Fix Released
llvm-toolchain-3.8 (Ubuntu)

Bug Description

SRU acceptance criteria: the example successfully links.

On updating ubuntu from 15.04 to 15.10, I see changes in how clang resolves references to some libraries. (I think this is not an ubuntu question but rather a clang question and that I've missed some subtlety on how clang has recently changed. I suspect initially that this is related to the gcc-5 ABI changes, but I'm not sure how to proceed.)

Here's a tiny test example designed only to tickle the phenomenon:

#include <jsoncpp/json/json.h>
#include <iostream>

int main(int argc, char *argv[]) {
    std::cout << argc << " - " << argv[0] << std::endl;
    Json::Reader reader;
    Json::Value root;
    reader.parse("", root, false);
    std::cout << reader.getFormattedErrorMessages() << std::endl;
    return 0;

If I compile like this

clang++ -ggdb3 -Wall -Wextra -std=c++14 -o json_test -ljsoncpp

/tmp/json_test-680d3a.o: In function `main':
/tmp/ undefined reference to `Json::Reader::getFormattedErrorMessages() const'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

And yet the definition appears to be present:

jeff@birdsong:src $ objdump -TC /usr/lib/x86_64-linux-gnu/ | grep getFormatted
000000000000e190 g DF .text 00000000000004d2 Base Json::OurReader::getFormattedErrorMessages[abi:cxx11]() const
000000000000dc70 g DF .text 00000000000004d2 Base Json::Reader::getFormattedErrorMessages[abi:cxx11]() const
jeff@birdsong:src $

The abi:cxx11 suggests I might at least try this

clang++ -ggdb3 -Wall -Wextra -std=c++11 -o json_test -ljsoncpp

but same error. On the other hand, this works fine:

g++ -ggdb3 -Wall -Wextra -std=c++14 -o json_test -ljsoncpp

Fwiw, here's version info:

jeff@birdsong:tmp $ g++ --version
g++ (Ubuntu 5.2.1-22ubuntu2) 5.2.1 20151010
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO

jeff@birdsong:tmp $ clang++ --version
Ubuntu clang version 3.6.2-1 (tags/RELEASE_362/final) (based on LLVM 3.6.2)
Target: x86_64-pc-linux-gnu
Thread model: posix
jeff@birdsong:tmp $

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: libjsoncpp-dev 0.10.5-1
ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3
Uname: Linux 4.2.0-16-generic x86_64
ApportVersion: 2.19.1-0ubuntu3
Architecture: amd64
CurrentDesktop: i3
Date: Mon Oct 26 12:00:40 2015
 gcc-5-base 5.2.1-22ubuntu2
 libc6 2.21-0ubuntu4
 libgcc1 1:5.2.1-22ubuntu2
 libjsoncpp0v5 0.10.5-1
 libstdc++6 5.2.1-22ubuntu2
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-10-23 (2 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: libjsoncpp
UpgradeStatus: Upgraded to wily on 2015-10-23 (2 days ago)

Jeff Abrahamson (jeff-purple) wrote :

assigning to clang

affects: libjsoncpp (Ubuntu) → llvm-toolchain-3.8 (Ubuntu)
affects: libjsoncpp (Debian) → llvm-toolchain-3.8 (Debian)
Changed in llvm-toolchain-3.8 (Debian):
status: Unknown → Confirmed
Matthias Klose (doko) wrote :

yes, clang is not yet aware of the GCC5 mangling

Changed in llvm-toolchain-3.8 (Ubuntu):
status: New → Confirmed
Changed in llvm-toolchain-3.8 (Ubuntu):
importance: Undecided → Medium
Matthias Klose (doko) on 2016-07-09
description: updated
Matthias Klose (doko) on 2016-07-09
Changed in llvm-toolchain-3.8 (Ubuntu Xenial):
status: New → Confirmed
Launchpad Janitor (janitor) wrote :

This bug was fixed in the package llvm-toolchain-3.8 - 1:3.8.1-3ubuntu1

llvm-toolchain-3.8 (1:3.8.1-3ubuntu1) yakkety; urgency=medium

  * Merge with Debian; remaining changes:

llvm-toolchain-3.8 (1:3.8.1-3) unstable; urgency=medium

  * Add -gsplit-dwarf to CXXFLAGS to workaround the memory allocation
    issue on i386 (hopefully)

llvm-toolchain-3.8 (1:3.8.1-2ubuntu2) yakkety; urgency=medium

  * Add support for gcc's attribute abi_tag (needed for compatibility with
    GCC 5's libstdc++); taken from the trunk. Closes: #797038. LP: #1510042.

 -- Matthias Klose <email address hidden> Sat, 09 Jul 2016 17:19:37 +0200

Changed in llvm-toolchain-3.8 (Ubuntu):
status: Confirmed → Fix Released

Hello Jeff, or anyone else affected,

Accepted llvm-toolchain-3.8 into xenial-proposed. The package will build now and be available at in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at . Thank you in advance!

Changed in llvm-toolchain-3.8 (Ubuntu Xenial):
status: Confirmed → Fix Committed
tags: added: verification-needed
Changed in llvm-toolchain-3.8 (Ubuntu Xenial):
importance: Undecided → Medium

the provided example now links.

tags: added: verification-done
removed: verification-needed

The verification of the Stable Release Update for llvm-toolchain-3.8 has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

This bug was fixed in the package llvm-toolchain-3.8 - 1:3.8-2ubuntu4

llvm-toolchain-3.8 (1:3.8-2ubuntu4) xenial-proposed; urgency=medium

  * SRU:
  * Add support for gcc's attribute abi_tag (needed for compatibility with
    GCC 5's libstdc++); taken from the trunk. Closes: #797038. LP: #1510042.

 -- Matthias Klose <email address hidden> Sat, 09 Jul 2016 13:22:59 +0200

Changed in llvm-toolchain-3.8 (Ubuntu Xenial):
status: Fix Committed → Fix Released
Daniel van Vugt (vanvugt) wrote :

This should have been done as bug 1488254, but glad to have a fix.

summary: - linking against -ljsoncpp fails with clang
+ clang++ no longer ABI-compatible with g++
Changed in llvm-toolchain-3.8 (Debian):
status: Confirmed → Fix Released
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