Re: backwards incompatibility

[Thomas Koenig <tkoenig@netcologne.de>]

Hi Dave,

> It's quite a pain for supporting research systems that the gfortran
> module format changes incompatibly with every (?) new version.

A lot of releases, yes. The problem is that we use a lot of positional
parameters in the files.

I have given a little thought of how to get around that by using some
sort of keyword-value scheme, which by definition are almost infinitely
extensible.

Another possibility would be to write out INTERFACE blocks as *.mod
files, which could then be re-read and re-parsed.

Just two problems: To a) get the design right, and b) get the
implementation right.  This would take a lot of effort, and the
manpower simplfy isn't there (and it hasn't figured high on the
list of priorities).

Of course, volunteers are always welcome.

> For
> instance, you can't mix development packages built with the RHEL system
> compiler with the more recent "devtoolset" compiler needed for hardware
> support.  As far as I know, the proprietary compilers don't have the
> same issue.  I can't find anything written about that, but I haven't
> tried to understand the implementation.  Is there something written?

It's in module.c, no documentation of gfortran's module file has
ever been done. Volunteers welcome...

> Version 8 makes the situation worse by breaking run time compatibility,
> not just build-time, with a different libgfortran shared library
> version.

This had to be done in order to fix long-standing bugs, and to allow
Fortran 2008 compliance.  We tried to stuff as much as possible into
this release, to avoid breaking binary compatibility for as many
releases as possible.

> That already caused considerable disruption with Fedora
> packaging after the switch to GCC 8.

What's the problem? Shipping two versions of shared libraries together
cannot be that hard, can it? OpenSUSE tumbleweed, which already
ships a pre-gcc8, manages this fine.

> With ELF, can't you use versioned
> symbols to avoid a new soname, like libgcc and libgomp do?

There are other systems which command equal attention - AIX, cygwin,
MacOS. Of course, volunteers are always welcome...

Regards

	Thomas