Am Mittwoch, den 10.02.2021, 10:32 -0800 schrieb Richard Smith:
> On Wed, Feb 10, 2021 at 12:29 AM Uecker, Martin via Liaison <
> liaison_at_[hidden]> wrote:
>
> > Am Mittwoch, den 10.02.2021, 07:43 +0100 schrieb Martin Uecker:
> > > Am Dienstag, den 09.02.2021, 15:36 -0800 schrieb Hans Boehm via Liaison:
> > > > On Tue, Feb 9, 2021 at 2:57 PM Joseph Myers via Liaison <
> > > > liaison_at_lists.isocpp.org> wrote:
> > > > A further complication (or simplification, depending on how you look
> >
> > at it)
> > > > is that the ABI story here is currently badly broken for everything but
> > > > simple types with size == alignment. The upside is that we can probably
> > > > change more than one might expect, so long as we leave the simple (and
> >
> > by
> > > > far most common) case alone. Everything else is largely broken and
> > > > hopefully unused anyway.
> > > >
> > > > All of which is an argument to properly discuss this at a meeting ...
> >
> > https://godbolt.org/z/5jo3aY
> >
> >
> > Here is a godbolt link for a test program. I tested only x86 on
> > gcc/clang/icc
> > and ABI is already broken. For basic types it works. For complex
> > float/double
> > alignment changes. Atomic struct types are not supported in ICC at all
> > and ABI is inconsistent between GCC C / GCC C++ / clang C++ on the one
> > side and clang C on the other (so also between clang C and C++!).
> >
>
> I've not run through all the cases but I don't think that's accurate.
> Rather, I think we have:
>
> GCC C _Atomic and libstdc++ std::atomic behave the same
> Clang C _Atomic, C++ _Atomic, and libc++ std::atomic behave the same
>
> (Note that the Clang on godbolt uses libstdc++ by default.)

Ok, thank you for the correction. This makes sense.

Martin


> So yes, a complete desaster.
> >
>
> Agreed. The psABI documents still haven't been updated to properly address
> atomic size and alignment, years later. :-(
>