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Subject: Re: libgfortran.so SONAME and powerpc64le-linux ABI changes
To: Michael Meissner <meissner@linux.ibm.com>,
 Jakub Jelinek <jakub@redhat.com>, fortran@gcc.gnu.org, gcc@gcc.gnu.org,
 Tobias Burnus <tobias@codesourcery.com>,
 Segher Boessenkool <segher@kernel.crashing.org>,
 David Edelsohn <dje.gcc@gmail.com>
References: <20211004100754.GL304296@tucnak>
 <YV5rGhDBjX3IxMlX@toto.the-meissners.org>
From: Thomas Koenig <tkoenig@netcologne.de>
Message-ID: <3dacfdf6-6b23-f307-969a-94265b506edb@netcologne.de>
Date: Thu, 7 Oct 2021 08:08:21 +0200
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On 07.10.21 05:35, Michael Meissner via Fortran wrote:
> I tried this at one point.  There are a lot of hidden assumptions that the kind
> number is the number of bytes.  I'm sure it can be tracked down, but the
> problem is with these assumptions is you can't prove a negative (i.e. you never
> know that you've missed some).

So, summing up from the Fortran side, I'd say the best course of action
is to

- make KIND=16 into IEEE QP

- bump the SONAME on on affected systems on POWER and nowhere else

- have a preprocessor flag so we can #ifdef out code which is relevant
   only there

- provide a CONVERT option (have to think of a suitable syntax) to
   do unformatted I/O either in IEEE QP or double double, but only
   on affected systems, so people can set this either via a CONVERT
   option on open or an environment variable.  For OPEN, we should
   extend the existing one, for an environment variable, I'd say
   we should use a new one and reuse the existing parsing routines.

Sounds like a reasonable minimum of user pain to me.

The rest I'll leave to the experts in all things ABI and POWER :-)