Bug#875618: openblas: please enable build on s390x

[Sébastien Villemot]

[CC’ing the debian-s390 at lists.debian.org list; s390 folks, please keep the bug
in CC on replies]

Dear Graham,

On Tue, Sep 12, 2017 at 07:28:04PM +0200, Graham Inggs wrote:
> Source: openblas
> Version: 0.2.20+ds-1
> Severity: wishlist

> From Changelog.txt in OpenBLAS 0.2.20:
> 
> IBM Z: * New target z13 with BLAS3 optimizations
> 
> I have just checked, and openblas/0.2.20-3 builds successfully on
> zelenka.debian.org.
> Please enable building on s390x.

Unfortunately it does not look that simple. OpenBLAS is optimized for z13, but
our s390x port is supposed to support all the z systems (see [1]).

In particular, the OpenBLAS build system adds the "-march=z13 -mzvector"
compilation flags. If I remove them, then the package fails to build on
zelenka: it complains about unknown assembly instructions, which are not
present on old z-systems. This is the proof that OpenBLAS cannot produce a
binary generic enough for our s390x port.

So unless I am missing something, it’s not possible to enable building for
s390x until 1) OpenBLAS supports older z-systems or 2) the hardware
requirements for the Debian s390x port are upgraded.

Best,

[1] https://www.debian.org/releases/stable/s390x/ch02s01.html.en#idm45373715987328

-- 
⢀⣴⠾⠻⢶⣦⠀  Sébastien Villemot
⣾⠁⢠⠒⠀⣿⡁  Debian Developer
⢿⡄⠘⠷⠚⠋⠀  http://sebastien.villemot.name
⠈⠳⣄⠀⠀⠀⠀  http://www.debian.org
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