[Distutils] Wheel files for PPC64le

[Nick Coghlan]

On 24 March 2017 at 05:00, Leonardo Bianconi <
leonardo.bianconi at eldorado.org.br> wrote:

> Hi all!
>
> I have been discussed the creation of a PEP, that describes how to create
> wheel
> files for the PPC64le architecture on wheel-builders
> (https://mail.python.org/pipermail/wheel-builders/) since January
> (https://mail.python.org/pipermail/wheel-builders/2017-January/000245.html
> ).
>

Thanks Leonardo!


>
> As all discussion from that list are done, the next step is it be reviewed
> here, and then create a draft on github,


You can submit the PR to the PEPs repo whenever you're ready - it's
actually handy to have the PEP number assigned fairly early as a convenient
reference for the proposal.



> The ``manylinux3`` policy
> =========================
>
> Based on PEP 513 [1]_, the policy follows the same rules and library
> dependencies, but with the following versions for backward compatibility
> and base Operational System:
>
> * Backward compatibility versions:
>     GLIBC <= 2.17
>     CXXABI <= 1.3.7
>     GLIBCXX <= 3.4.9
>     GCC <= 4.8.5
>
> * Base Operational System:
>   The stock O.S. release need to be the CentOS 7 [4]_, as it is the first
>   CentOS release available for PowerPC64 little endian.
>
> The tag version for ppc64le architecture starts with 3 (``manylinux3_``),
> as it
> is supposed to be the version to match the CentOS 7 [4]_ in the future of
> the
> tag for x86_64/i686 architecture. There is the possibility of both tags
> diverge
> until it reaches the version 3, then a new PEP may be create to converge
> both to the manylinux baseline.
>

Having manylinuxN consistently align with CentOS(N+4) seems reasonable to
me for simplicity's sake, but there should be a discussion in the PEP
around how that aligns with ppc64le support on other LTS distros (mainly
Debian and Ubuntu).

Given the relative dates involved, I'd expect manylinux-style binaries
compiled on CentOS 7 to also work on Ubuntu 14.04, 16.04 and Debian 8, but
the PEP should explicitly confirm that the nominated symbol versions above
are available on all of those distros.


> Compilation of Compliant Wheels
> ===============================
>
> As compiling wheel files that meet the ``manylinux3`` standard for
> PowerPC64
> little endian requires a specific Linux distro and version, the following
> tool
> is provided:
>
>
> Docker Image (Will be implemented when CentOS be available on Docker)
> ------------
>
> The Docker Image is based on CentOS 7 [4]_, which is the first PowerPC 64
> little endian CentOS release. The Image contains all necessary tools in the
> requested version to build wheel files (gcc, g++ and gfortran 4.8.5).
>

These seem to be present now: https://hub.docker.com/r/ppc64le/centos/tags/

I'm not clear on the provenance of the 'ppc64le' user account though, so
I've asked for clarification: ttps://
twitter.com/ncoghlan_dev/status/845099237117329408



> Platform detection for Installers
> =================================
>
> The platform detection is almost the same as described in PEP 513 [1]_, but
> with the following proposed change:
>
> 1. Add the platform ppc64le in the platform list as a compatible one:
>    [``linux-x86_64``, ``linux-i686``, ``linux-ppc64le``]
> 2. Add an if to switch architecture and consider the correct version of the
>    GLIBC on ``return have_compatible_glibc(2, 5)``.
>

I don't think is quite that simple, as installers need to be able to figure
out:

- on manylinux3 compatible platforms, prefer manylinux3 to manylinux1
- on manylinux3 *in*compatible platforms, only consider manylinux1

And that means asking the question: when combined with the option of the
distro-provided `_manylinux` module, is "have_compatible_glibc(2, 5) and
not have_compatible_glibc(2, 17)" an adequate check for the latter case?
(My inclination is to say "yes", but it would be helpful to have some more
concrete data on glibc versions in different distros of interest)

Beyond that, I think the main open question would be: do we go ahead and
define the full `manylinux3` specification now? CentOS 7+, Ubuntu 14.04+,
Debian 8+ compatibility still covers a *lot* of distros and deployments,
and doing so means folks can bring the latest versions of gcc to bear on
their code, rather than being limited to the last version that was made
available for RHEL/CentOS 5 (gcc 4.8).

Going down that path would also means things would be simpler on the PyPI
front - it could just allow manylinux3 for any architecture and let
installers decide whether or not to use them.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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