Re: libgfortran.so SONAME and powerpc64le-linux ABI changes

[David Edelsohn <dje.gcc@gmail.com>]

On Wed, Oct 6, 2021 at 11:19 AM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> On Wed, Oct 06, 2021 at 08:59:53AM +0200, Thomas Koenig wrote:
> > On 05.10.21 23:54, Segher Boessenkool wrote:
> > >>There is also the issue of binary data.  If some user has written
> > >>out data in double double and wants to read it in as IEEE quad,
> > >>the results are going to be garbage.  Another option for CONVERT
> > >>might be the solution to that, or, as you wrote, having a
> > >>REAL(KIND=15).  It should be inaccessible via SELECTED_REAL_KIND,
> > >>though.
> > >
> > >That means flipping the default on all PowerPC to no longer be double-
> > >double.  This means that you should have IEEE QP work everywhere, or the
> > >people who do need more than double precision will have no recourse.
> >
> > I think we can exclude big-endian POWER from this - they do not have
> > IEEE QP support, correct?  So, exclude that from the SONAME change.
>
> Not correct, no.  IEEE QP works fine in either endianness.

This needs to be described with more granularity.  IEEE QP
instructions work with either endianness.

IEEE QP is enabled and supported for PPC64 LE Linux on Power.  The
transition is under discussion.

PPC64 BE Linux on Power does not define IEEE QP.  The ABI could be
updated and IEEE QP could be enabled, but PPC64 BE is not planning
future releases from Linux distros.

IEEE QP for PPC64 FreeBSD on Power is an open question for the FreeBSD
community.

AIX on Power will continue to use double-double long double format.
GCC, LLVM, IBM Open XL and IBM XL compilers will continue to implement
and support the double-double format on AIX.

Thanks, David

P.S. This is my personal understanding and not an official statement
of support or product guidance from IBM.