libgfortran.so SONAME and powerpc64le-linux ABI changes

Segher Boessenkool segher@kernel.crashing.org
Fri Oct 15 22:36:46 GMT 2021


Thank you for writing this out Bill!

On Fri, Oct 15, 2021 at 08:50:08AM -0500, Bill Schmidt wrote:
> Longer term, we have the question of supporting more Power targets.  AIX will continue to
> use only double-double.

Yes.  So it will be virtually no cost to continue supporting
double-double on all targets (implementation cost that is -- maintenance
cost will actually be negative for keeping it for a while, old data
sticks around for a very long time.)

> It is agreed that it would be useful for 32- and 64-bit BE Linux
> to support IEEE QP as well, on some future timeline.  The first step towards this is to
> develop and document ABI for IEEE QP on those targets.  The simplest approach that everyone
> seemed to like is for these ABIs to require AltiVec support in order for IEEE QP to be
> supported.  This allows parameters and return values to always be passed in vector registers,
> whether implemented with hardware instructions or a soft-float library.  libquadmath can
> be built for these targets.

This is a great choice for the ABIs that have AltiVec enabled, yes.  It
requires almost no modification to the parameter passing for them
(ignoring the obvious fact that it changes where long double is passed,
if long double now is IEEE QP; similarly, KIND=16), it can be just the
same as anything else passed in VRs.

At a later date we can consider having QP for ABIs without AltiVec as
well, if there is any interest in that.  Since there exists no such
thing yet, having QP passed in VRs will be easy to do everywhere :-)


Segher


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