github-hosted runner, win32-arm64 fails to due to missing tool cache and permissions errors

[starpit]

Description:
When using GitHub-hosted runners, with win32-arm64, this action always seems to fail. I have tried "3.x", "3.11", "3.12", and "3.13". In all cases, the action finds no such python in the hosted tool cache, then tries to download the python build (succeeds), and then install it (fails with permissions issues, presumably, while editing the windows registry).

No problems with x64 and x86.

Action version:
v5

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Tools version:

3.x, 3.11, 3.12, 3.13

Repro steps:
Try win32 with arm64.

Expected behavior:
It should be in the tool cache, no?

Actual behavior:
Not in tool cache, and subsequent failure to install the downloaded tool.

Example output:
https://github.com/IBM/spnl/actions/runs/17279551436/job/49044713563

[gowridurgad]

Hi @starpit,
Thank you for creating this issue. We will investigate it and provide feedback as soon as we have some updates.

[gowridurgad]

Hi @starpit, Just to clarify:
The windows-latest GitHub-hosted runner is based on x64 architecture and does not support ARM64 natively.
If you specifically need to run your workflow on Windows ARM64, you have two options:

1. Set up a self-hosted runner on a Windows ARM64 machine, which allows you to customize the environment and architecture according to your requirements.
2. Use the windows-11-arm runner, which provides a managed Windows ARM64 environment.

Please let us know if you have any further questions or need assistance!

[starpit]

Thanks for looking into this. It still seems like there is a problem. Why is there an x64 version in the hosted tool cache? Even so, shouldn't setup-python, when provided with architecture: arm64 detect this and... somehow fix it?

🐍 Found CPython 3.13 at C:\hostedtoolcache\windows\Python\3.13.5\x64\python.exe, CPython 3.12 at C:\hostedtoolcache\windows\Python\3.12.10\arm64\python.exe

[gowridurgad]

Hi @starpit, thanks for following up!

After testing the Windows ARM64 runner, we can confirm it does include both ARM64 and x64 Python builds in the hosted tool cache. Here is a reference run. This is expected because the runner can run x64 binaries via emulation. However, only the ARM64 versions are intended to be used natively when you specify architecture: 'arm64'.

We tested this and confirmed it correctly detects and uses the ARM64 build from the tool cache and completes successfully without attempting a fallback download. Here is a reference run.
So to clarify, x64 Python versions are present in the tool cache, but they are not selected when architecture: 'arm64' is explicitly provided.

If you’re still encountering issues, could you please confirm which runner label you’re currently using? For ARM64 compatibility, we recommend using runs-on: windows-11-arm.

[starpit]

Thanks for digging! It looks like this is a maturin issue. PyO3/maturin#2692

Though: why does the hosted tools cache contain x64 3.13 and arm64 3.12? At least this is what is detected (by maturin) via py --list-paths. I would have expected to see x64 and arm64 of both? Or at least arm64 of both, since after all this is a windows-11-arm image...

[gowridurgad]

Hi @starpit, to clarify, the tool cache on the windows 11 arm runner currently includes:

• Python 3.13: both x64 and arm64 builds
• Python 3.12: only the arm64 build

The availability of specific Python versions and architectures in the tool cache depends on how the ARM64 runner image is built and maintained, which in turn relies on upstream support and availability at the time the image is created.

As you noted in PyO3/maturin#2692, maturin may incorrectly detect and attempt to use an x64 Python version when building for ARM64 especially since both architectures are present in the cache leading to misconfiguration during builds. To avoid this, as suggested in PyO3/maturin-action#346, set architecture: 'arm64' . This ensures the correct native ARM64 Python version is selected and prevents fallback to the wrong architecture.

If you observe missing or inconsistent availability of Python versions or architectures on the windows 11 arm runner, we recommend opening an issue in the @actions/partner-runner-images repository for further investigation.

[gowridurgad]

Hi @starpit, Just a gentle reminder regarding this issue, If you have any updates or need further assistance, Please let us know.