Python on Windows ARM64

Core Development
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We’ve got our Windows ARM64 buildbot back, thanks to @zware for looking after it. So the plan to make it the default continues as intended.

(Bearing in mind that the change for that is now in the Python install manager, and so will happen in time for 3.15, rather than as part of 3.15. People who want it to be their default now can already set PYTHON_MANAGER_DEFAULT_PLATFORM=-arm64 or "default_platform": "-arm64" in their configuration file).

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Talking with folks at EuroPython and given the fact that lately I’m following closely this platform, I’ve come to the conclusion that I’m volunteering myself to look after this platform.

I don’t have a ton of experience with Windows but I do have permanent access to a Windows on Arm machine (although virtualised with Parallels) and I can take care of it, if it’s needed.

I’ve talked with @chris-eibl and promised to tag him here in case he wants to join the conversation.

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Thanks @diegor, it’ll make a big difference to know that you’re on board for the platform specifically. (Even more core devs are also welcome, though access to the hardware is of course the limiting factor.)

It also means we can start looking at promoting its PEP 11 tier, which is probably worth doing immediately (in time for 3.15).

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Great. If you need help just ping me. @zware can give me access to his build bot. If it helps, I could set up another one in the future if needed (and I gain some Azure credits).

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Have we got you set up with the VS Subscription for core devs yet? Send me an email with your email login address for <my.visualstudio.com> if you need it. That comes with enough monthly credits to run a couple of buildbots, or just to have VMs for testing.

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I’ve created the PR, but we need to wait the approval of the SC: PEP 11: promote aarch64-pc-windows-msvc to Tier 2 by diegorusso · Pull Request #5046 · python/peps · GitHub

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Can you open a ticket on GitHub - python/steering-council: Communications from the Steering Council · GitHub? That’ll make sure it gets added to the queue!

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Thanks, this has been created: Update PEP 11: bump Windows on Arm to Tier 2 · Issue #359 · python/steering-council · GitHub

Let me know if you need anything else.

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The following is mostly a small moan and probably not useful for anyone to respond to.

I’ve hit a second opaque MSVC bug with Windows on ARM. As before, this is a somewhat obscure system which fairly few people have access to. It’s painful to debug solely via Github Actions and most other ways of trying to debugging it seem to involve paying money to Microsoft and/or ARM. (The same could arguably be said for OS X but currently it’s causing me problems much less frequently). My previous compiler bug did get fixed, but on a ~8 month timescale.

So I guess the message is: Windows on ARM64 remains a fairly awkward platform to support.

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30

I don’t think you have to activate Windows anymore, it will just keep working indefinitely? I’ve had an unactivated Windows ARM64 VM for over a year for debugging occasional Windows issues in my projects. As far as I can tell, it shows a popup when you open the settings, and shows a faint watermark in the bottom right sometimes, but doesn’t otherwise prevent anything I’ve needed for this occasional development work.

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Could you share some details/a link anyway? I’d like to make sure the pain gets passed along to the team responsible for the bug, otherwise they’ll just assume that everyone’s happy (because we’re all too good at finding workarounds).

Unfortunately, most of the delay is waiting for updates to the Github images, which often get delayed due to bugs in other parts of the image. There are some improvements to “always install and use the latest compilers on demand”, but the team still don’t believe we should be able to do it without a proper Visual Studio install (even internally… they recently took away the “easy install” feed we used to have).

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Developer Community so I did report it to the correct place (although didn’t spend a lot of effort making it usefully minimal for them)

In fairness to the MSVC team, we did also have a GCC bug recently where they decided to optimise true->false and false->true[1]. So it’s not like the rest of the world is bug free (and Cython itself obviously has it’s fair share of bugs) - it’s just a little harder to find them on more obscure platforms.

  1. This is only a slight exaggeration of the actual issue for dramatic effect… ↩︎

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I saw this thread randomly, and I also just ran into a compiler bug/regression, I’m pretty sure. I rented a Windows on ARM VM from Azure to figure out what was going on. Developer Community

Had to switch to an older compiler version in our CI: Fix Windows ARM test fail by Starbuck5 · Pull Request #4010 · pygame-community/pygame-ce · GitHub

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Maybe related: Windows Arm64 release build fails · Issue #153668 · python/cpython · GitHub
Also a problem during linking, but linker fails with OOM, and only for release builds.
Not yet solved, just checked latest insider build …

Windows on ARM VM from Azure

That’s what I do as well.