Re: [boost] ABI issues with -std

Subject: Re: [boost] ABI issues with -std
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2018-08-19 20:19:52

On Sun, Aug 19, 2018 at 6:17 PM, Peter Dimov via Boost
<boost_at_[hidden]> wrote:
> At some point, we'll need to acknowledge the problem which results from
> building Boost with one -std and user code with another, and deal with it
> somehow, if just by documenting.
>
> Most of our libraries don't suffer from it at the moment but Boost.System
> does, because of my changes; its ABI changes between 03/11/14. So I'm going
> to take the initial hit. :-)
>
> POSIX platforms have long been able to ignore ABI issues so we don't mangle
> the library names there at all, but now whether one builds Boost for C++03,
> C++11 or C++14 matters, and there's nothing to prevent linking C++xx to
> C++yy. Even with --layout=versioned, the cxxstd level is not encoded.
>
> The fact that the default C++ standard differs between g++ and clang++
> doesn't help; when following the instructions of doing "b2 install", with
> g++6 and above you get C++14, but with g++5 or clang++ you get C++03. The
> latter is very rarely what one wants today.

Our libraries should build into binaries that are suitable for linking
with user's code in any C++ version, otherwise standard Boost binaries
in Linux distributions will be compatible only with one C++ version,
which is not practical.

Could you expand on what causes the ABI difference and why it can't be
unified? I know it may be ugly, but libstdc++ does maintain ABI
stability somehow, we could follow its example.

If we can't or don't want to make Boost.System ABI-portable then I'd
rather revert the changes to Boost.System and maybe create
Boost.System2 for C++11 and up.