pkg/wamr: Added support for THUMB_VFP in wamr Makefile

[bmewen]

Contribution description

Edited wamr Makefile to support THUMB_VFP

Testing procedure

Build and test with arduino-nano-33-ble (nrf52840 cpu) for THUMB_VFP mode and built with nrf51dk for THUMB mode.

Issues/PRs references

[benpicco]

Change looks good, you want to follow the commit title convention though, so plaese change the commit message to something like

pkg/wamr: add support for THUMB_VFP

You can do so with git rebase -i HEAD~2 - then you can also squash your commits.

[riot-ci]

Murdock results

✔️ PASSED

150058e pkg/wamr: Added support of THUMB_VFP

Success	Failures	Total	Runtime
10065	0	10066	14m:41s

Artifacts

• Documentation preview

[benpicco]

Thank you for the patch!

[maribu]

Nit picking: Would it be possible to disable hardware FPU support if that is provided, and is this something that we need to be prepared for?

I think just using FEATURES_USED instead of FEATURES_PROVIDED would work. But there is a CI test that will fail if anyone uses the FEAUTRES_USED variable, which would prevent this from getting merged. I wonder if that CI check has outlived its usefulness anyway.

In either case, I think merging this is an improvement and this concern should not block this. But maybe we could add a follow up, if there is any merit to my concern.

[bmewen]

Regarding the FEATURES_USED vs FEATURES_PROVIDED, since from my understanding VFP is an extension and therefore provides the same capabilities as the normal architecture I think that as long it doesn't create performance issues it should be used if the feature is provided.

[maribu]

Note that the ABI between hardfp and softfp is not compatible. You can safely run softfp code on a hardfpu MCU (if floats are actually used softfp will be both slower and larger, though). But you cannot link objects compiled for a softfp ABI together with objects compiled for a hardfp ABI.