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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Making the same mistake as the broken C interface to fortran
Date: Tue, 02 Jul 2019 21:57:23 +0100
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Date: 2019-07-02T21:57:23+01:00
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Chris M Moore <zmower@ntlworld.com> writes:

> Read this interesting article today:
>
> https://lwn.net/SubscriberLink/791393/41d57555202e8cdb/
>
> Synopsis: C interfaces to Fortran makes some assumptions about how to
> call fortran ABIs (I don't need to pass the hidden length parameter if
> its a character*1) but now Gfortran has optimisations which assume a
> different calling convention (Thou shalt pass the hidden length).
>
> There are work arounds (compile fortran with
> ‑fno‑optimize‑sibling‑calls) but it seems that the proper fix is to
> pass the hidden length parameter.
>
> I had a quick look at the LAPACK bindings and they both seem to use
> Ada characters. :/

The code generated with Convention=Fortran should abide by the ABI, and
if that says to pass a hidden length parameter then that's what should
happen.

I don't know enough x86_64 (or thumb) assembler to be at all sure, but
it looks to me as though no length parameter gets passed.