Windows ARM64 support

[alinpahontu2912]

Hi, I'm writing to ask about potential support for Windows ARM64 devices in future releases.
Currently, the anycpu wheel installed on Windows ARM64 is only around 25KB and lacks the libsndfile DLL, which makes the package unusable on this platform. From what I can see libsndfile DLLs for WinARM64 appear to be available. GitHub Actions now also supports Windows ARM64 runners, so it seems like it should be possible to build and publish a proper win_arm64 wheel—similar to what's already done for other platforms.

Please consider adding support for this, as it would greatly improve usability on Windows ARM devices.

Thanks for your work on the project!

[bastibe]

Neither numpy nor cffi support Windows ARM64. I have an ARM64 build of libsndfile ready and an ARM64 device for testing, but without Numpy and CFFI, there's no use.

Furthermore, Python currently does not distinguish between native-ARM64 and x64-running-on-ARM64, so even if numpy and CFFI did support Windows ARM64, there'd be no way for soundfile to distinguish between running natively and emulated.

[sabonerune]

Numpy and cffi appear to be in the process of providing Windows ARM64 wheels.
python-cffi/cffi#109
numpy/numpy#22530
I think it's about time to start preparing.
There are several ideas for identifying DLLs.

1. sysconfig.get_platform()
   Inaccurate
   https://docs.python.org/3/library/sysconfig.html#sysconfig.get_platform
   It's simpler and more accurate than environment variables.
   It cannot be used with versions less than 3.2, in which case it is x86.

try:
    from sysconfig import get_platform
    is_arm64 = get_platform() == "win-arm64"
except ImportError:
    is_arm64 = False

NOTE: #462 already broke support below 3.5.
NOTE2: I can't find any issues or PRs to fix the build, and if this continues, the package will be released with the wrong metadata!

2. os.environ["PROCESSOR_ARCHITECTURE"]
   Maybe it's inaccurate.
   https://learn.microsoft.com/windows/win32/winprog64/wow64-implementation-details

3. win32 API
   Use Win32API's GetSystemInfo with ctypes.
   It's accurate but tedious.
   https://learn.microsoft.com/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsysteminfo

[bastibe]

get_platform reports arm64, even if we're running an x64 python on an arm64 machine.

[sabonerune]

On Windows sysconfig.get_platform() gets the information from sys.version.

The following code returns win-amd64 when run with Python x64 on the windows-11-arm runner.
python -c "import sysconfig;print(sysconfig.get_platform())"

[bastibe]

Interesting. My Surface 11 reports arm64, even if running x64 python. I wonder what's the difference to the windows-11-arm runner.

[sabonerune]

I couldn't find the answer.

https://github.com/python/cpython/blob/3.13/Lib/sysconfig/__init__.py#L611-L618
sysconfig.get_platform() may return sys.platform.

I thought this code would only run in very rare cases if you built it in a way that is not officially supported.
This assumption appears to have been incorrect.

[bastibe]

AFAIK, Windows supports cross-platform DLL loading, so it might actually be possible to load ARM64 DLLs from an x64 python. We'll try it out once numpy and CFFI are available.

[alpinedelight]

@sabonerune's method seems to work on my machine.

py -3.13-arm64 -c "import sysconfig;import os;print(sysconfig.get_platform(),' ',os.getpid());input('x')"
py -3.12 -c "import sysconfig;import os;print(sysconfig.get_platform(),' ',os.getpid());input('x')"

I added getpid() and input() to get PID and keep the process open to inspect in taskmanager.

...

AFAIK, Windows supports cross-platform DLL loading, so it might actually be possible to load ARM64 DLLs from an x64 python. We'll try it out once numpy and CFFI are available.

I can also confirm it (Windows or CFFI?) isn't happy using DLL's interchangeably - you need the right DLL.

[sabonerune]

@alpinedelight
The problem is that sysconfig.get_platform() may not work as expected.
It should not be used unless you can confirm that the conditions under which it does not work are unusual and rare.

[alpinedelight]

Tested python versions 3.8, 3.10, 3.12, 3.13 from Microsoft store and installing directly (MSI and winget).
Seem to get the right output when comparing to what Windows reports in task manager.
@bastibe where/how did you install yours?

[bastibe]

Whatever caused that behavior earlier, it seems to have been fixed. I just reinstalled a new version of Python, and now sysconfig.get_platform() correctly reports either ARM64 or AMD64, depending only on the version of Python.

Good.

We're still missing official arm64 builds for cffi, but there are experimental builds available at https://github.com/cgohlke/win_arm64-wheels.