Bug 571600 – sys-devel/clang, sys-devel/llvm - ABI incompatibilty with libstdc++ from sys-devel/gcc-5* due to missing abi-tag support

• Product: Gentoo Linux
• Status: RESOLVED UPSTREAM

[Description Matthias Maier 2016-01-11 22:25:29 UTC]

clang [1] currently does not support the new attribute __abi_tag__ [2] introduced by gcc-5* [3] for dual-abi support.

Unfortunately, this makes clang ABI-incompatible with gcc-5*-compiled code due to different mangling of symbols (that happen to be annotated with the __abi_tag__ attribute):

For example a global symbol
  std::string foo;
is now named `foo[abi:cxx11]' by g++-5* but `foo' by clang.

Gentoo enables the new dual-abi by default.

This is very unfortunate because it renders clang++ (almost) useless [4] on systems with gcc-5*.


[1] https://llvm.org/bugs/show_bug.cgi?id=23529
[2] https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Attributes.html
[3] https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html
[4] With the exception of -stdlib=libc++ and if the full c++ link-interface is compiled by clang, obviously.

[Comment 1 Michał Górny 2016-01-13 15:04:51 UTC]

Added, thanks.

[Comment 2 Michał Górny 2016-01-13 15:05:28 UTC]

Sorry, wrong bug.

[Comment 3 Matthias Maier 2016-01-21 19:34:46 UTC]

Created attachment 423550 [details, diff]
patch that adds abi_tag support (experimental)

This patch is a slightly modified version of the current state of the code
review [1] as of 2016/01/21.

It can be used as a workaround for everyone affected by simply saving it
to
  /etc/portage/patches/sys-devel/llvm/
such that it gets applied through the user_patch mechanism.

We should probably refrain from applying it unconditionally and wait for
upstream's decision/official merge.

[1] http://reviews.llvm.org/D12834

[Comment 4 Bernard Cafarelli 2016-03-14 09:41:36 UTC]

Well, at least there seems to be some upstream activity  (in trunk, not in 3.8):
* First part http://reviews.llvm.org/rL263015 was merged
* Second part has some review activity: http://reviews.llvm.org/D18035

I wonder how a 3.8 backport would behave here...

[Comment 5 Fabio Scaccabarozzi 2016-07-11 09:34:11 UTC]

Created attachment 440340 [details, diff]
Sema part of abi tag support for LLVM

[Comment 6 Fabio Scaccabarozzi 2016-07-11 09:34:31 UTC]

Created attachment 440342 [details, diff]
Mangler part of abi tag support for LLVM

[Comment 7 Fabio Scaccabarozzi 2016-07-11 09:39:10 UTC]

Please see the attached patches.
They were taken from Arch and refreshed for dropping them into /etc/portage/patches:
https://git.archlinux.org/svntogit/packages.git/tree/trunk?h=packages/llvm

I hit bug #587640 when trying to compile rust with system-llvm USE, and realized it was due to this.
Using the patches, I'm finally able to compile rust with system-llvm, so the patches do work, they probably need some testing.
Note that both parts have been merged upstream now, so they should be included in 3.9.0 if I understood the workflow properly.
I tried backporting the patches myself, but a lot of the stuff was against trunk, which meant some functions didn't have the same signatures. Apparently that backporting work was already done in Arch Linux.

[Comment 8 Doug Goldstein (RETIRED) 2016-07-18 14:20:47 UTC]

*** Bug 587640 has been marked as a duplicate of this bug. ***

[Comment 9 Matthias Maier 2016-07-18 15:43:43 UTC]

(In reply to Fabio Scaccabarozzi from comment #7)

> Using the patches, I'm finally able to compile rust with system-llvm, so the
> patches do work, they probably need some testing.

Unfortunately, gcc-5* and gcc-6* have ABI incompatible implementations of the abi-tag feature (basically a bugfix in gcc-6*) [1]. The patchset for clang implements the gcc-6* version and thus does not support gcc-5*.

[1] https://llvm.org/bugs/show_bug.cgi?id=28511

[Comment 10 Matthias Maier 2016-08-02 17:25:25 UTC]

commit 6ccd97198cc1d33b13c6aa69e73ea06b69bf59d5
Author: Matthias Maier <[e-mail]>
Date:   Tue Aug 2 10:19:35 2016 -0500

    sys-devel/llvm: Backport abi-tag support, bug #571600
    
    This applies the abi-tag support patches to 3.8.1-r1.
    
    Unfortunately, gcc-5* and gcc-6* have slightly ABI incompatible
    implementations of the abi-tag feature (basically a bugfix in gcc-6*) [1].
    The patchset for clang implements the gcc-6* version and is thus not fully
    compatible with gcc-5*.
    
    [1] https://llvm.org/bugs/show_bug.cgi?id=28511
    
    Package-Manager: portage-2.2.28

[Comment 11 Michał Górny 2018-03-29 08:01:15 UTC]

I think there's nothing to do for us here. The mangling support is part of current upstream releases, and gcc<6 is no longer really supported anyway.