Remove 31/32-bit s390 Linux support (s390-linux-gnu triplet)

[tiran]

BPO	43179
Nosy	@tiran, @mcepl, @ambv, @stratakis, @glaubitz, @jrtc27
PRs	bpo-43179: Drop 31/32-bit Linux s390 platform support #24534 bpo-43179: Generalise alignment for optimised string routines #24624
Files	gcc-s390.txt: GCC macro definitions for Linux on Z in 31 bit mode gcc-s390x.txt: GCC macro definitions for Linux on Z in 64 bit mode

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-02-09.11:41:13.580>
labels = ['interpreter-core', '3.10']
title = 'Remove 31/32-bit s390 Linux support (s390-linux-gnu triplet)'
updated_at = <Date 2022-01-31.12:02:06.622>
user = 'https://github.com/tiran'

bugs.python.org fields:

activity = <Date 2022-01-31.12:02:06.622>
actor = 'fweimer'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2021-02-09.11:41:13.580>
creator = 'christian.heimes'
dependencies = []
files = ['49817', '49818']
hgrepos = []
issue_num = 43179
keywords = ['patch']
message_count = 56.0
messages = ['386709', '386983', '386984', '386985', '386986', '386996', '386997', '386999', '387000', '387002', '387003', '387004', '387005', '387006', '387008', '387009', '387010', '387019', '387021', '387022', '387025', '387038', '387093', '387094', '387095', '387096', '387097', '387114', '387130', '387132', '387156', '387161', '387162', '387165', '387167', '387176', '387202', '387203', '387227', '387255', '387257', '387258', '387261', '387262', '387263', '387265', '387456', '387457', '387458', '387459', '387460', '387465', '389103', '389104', '389887', '412198']
nosy_count = 9.0
nosy_names = ['christian.heimes', 'mcepl', 'Arfrever', 'lukasz.langa', 'fweimer', 'David.Edelsohn', 'cstratak', 'glaubitz', 'jrtc27']
pr_nums = ['24534', '24624']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue43179'
versions = ['Python 3.10']

[tiran]

configure.ac contains triplet definitions for s390 and s390x mainframes. While s390x (Linux on IBM Z) is still widely supported, s390 is not. s390 was released in 1990 and discontinued in 1998, https://en.wikipedia.org/wiki/IBM_System/390

Ariadne Conill from Alpine pointed out that:

Linux has not supported booting on traditional 31-bit s390 since
Linux 4.1 in 2015. If you can't boot s390 (not s390x) with a modern
kernel, it is absurd to demand that other projects support s390.

pyca/cryptography#5771 (comment)

I propose to remove check for __s390__ from configure.ac and configure.

We might also want to remove __alpha__, __hppa__, and __m68k__ at a later point. DEC hasn't been around for a long time.

[glaubitz]

I'm a Debian Developer and maintainer for multiple Debian Ports architectures.

Please don't remove support for Alpha, HPPA, m68k, ia64, PowerPC, SuperH, SPARC as we're still maintaining these in Debian.

Here are the latest build results for Python3.9 in Debian with build logs for all these architectures:

https://buildd.debian.org/status/package.php?p=python3.9&suite=sid

There are no issues reported and we heavily rely on Python.

[glaubitz]

And, FWIW, I generally don't quite understand what the problem with old triplet definitions in configure.ac are. I assume they don't hurt anyone, do they?

You never know what usecases your users have and as long as a code snippet doesn't interfere with other code, I don't see little point in removing it.

[tiran]

It's about setting expectations. For some users, the presence of a platform triplet implies support for a platform.

[glaubitz]

That's an argument I have personally never heard before and I have been dealing with a lot of architecture support in many packages.

FWIW, lots of upstream projects have targets which are officially supported and others which are there but not supported and that was never really a problem.

As long as the architectures are being maintained in the Linux kernel, GCC, binutils and glibc, they can be considered usable and maintained.

The m68k architecture for example has a very active and large community due to the popularity of retro computing. This has lead to efforts which will soon bring Rust support to M68k and the Amiga.

I therefore don't really understand what you gain when you make it harder for downstreams to use Python.

[tiran]

That's an argument I have personally never heard before and I have been dealing with a lot of architecture support in many packages.

I opened this ticket after a user told me that they grepped the source code of Python, found the string "s390", and concluded that s390 is still supported by us.

This ticket is really just about s390. I said that we *might* want to remove other platform at a *later* point. For now I don't mind to keep them. We could also put unsupported platforms behind a --enable-unsupported-platforms guard. The option would allow you to compile on retro platforms and serve as indicator that the platform is not supported by us.

[vstinner]

I propose to remove check for __s390__ from configure.ac and configure.

I don't see a big benefit of removing a few lines of configure.ac. It's not like it's a big maintenance burden.

It's about setting expectations. For some users, the presence of a platform triplet implies support for a platform.

I maintain https://pythondev.readthedocs.io/platforms.html : unofficial list of platforms and C compilateurs supported by Python, and the different kinds of support levels (supported, best effort, not supported).

[vstinner]

Does AIX support the s390 architecture?

[glaubitz]

I opened this ticket after a user told me that they grepped the source code of Python, found the string "s390", and concluded that s390 is still supported by us.

Because one user was surprised by a few lines in configure.ac, the conclusion is to remove support for that architecture?

That's a very odd justification.

If it really just affects configure.ac, I don't really see a point in removing them. Even in OpenJDK we keep such unofficial architectures in configure.ac (with my OpenJDK upstream maintainer hat on).

[tiran]

Does AIX support the s390 architecture?

The platform triplet is s390-linux-gnu, not AIX.

Because one user was surprised by a few lines in configure.ac, the conclusion is to remove support for that architecture?

You are misinterpreting my words. My initial posting explains that the hardware platform is no longer supported by any of our supported operating systems. I want to make it obvious that the platform has been dropped half a decade ago.