On Tue, Sep 18, 2018 at 08:46:46AM -0400, Richard Yao wrote: > > > On Sep 17, 2018, at 12:40 PM, Vadim A. Misbakh-Soloviov <gen...@mva.name> > > wrote: > > > > I'd prefer to wait another replies on the list for the main theme of this e- > > mail, but this problem also affects C (so, as **c**flags and C standards), > > so > > solution shoudn't be c++ specific, imho. > You would think that, but the C standard version does not effect ABI > compatibility. We had a very long discussion about this in OpenZFS because > the other platforms were using C99 while we had backported everything to C89 > on Linux because of the Linux kernel. No one could find a single example of > ABI breakage caused by mixing and matching C89 and C99 (C99 LKM and C89 > kernel). After a few years of not a single example being raised, the Linux > team lead opted to adopt C99. > > Now, there are flags affecting the ABI, but those are separate from the C > standard version. As for C++, mixing standard versions does go badly because > new language features require ABI changes. > >
Yes, since mixing standard versions is not so good, and many ebuilds hard-code it with append-cxxflags, I think it's worth discussing a better solution that will avoid unnecessary breakage. The big problem is going from C++14 to C++17 as mentioned before. The 'noexcept' became part of the mangled name. C++17 also removes features, so there will be code that will need to be changed to compile as well. If we have a system-wide setting, we can start warning upstreams about it at least when things break. Cheers, -Guilherme
