[RFC 0/2] Experimental kunit test for signal context handling

[Thomas Weißschuh]

Hi,

On Thu, Jun 26, 2025 at 09:57:12PM +0200, Benjamin Berg wrote:
> so I saw the UAPI testing framework patches and wondered whether I could
> hack up a kunit test for userspace signal mcontext handling. I already
> had some code, but never knew where to include it. Having it as a kunit
> test in this way seems nice as it makes running the test really simple.

Nice to hear that you find it useful.

> This is a very rough attempt with an extra patch to add sigaction
> support as that is needed by the test.
> 
> Note that this type of test could possibly be shared with the x86
> architecture (though UM does not support all features).

Can the expected feature detection be performed at runtime?
If so I would write the test as x86 kselftest in tools/testing/kselftests/x86/
and then also hook it up for kunit on UML and x86.
This gives you the advantages of all worlds.

For an example see [0]. That is still based on an old version of the framework,
so can't be used as-is. But you should get the idea.

> And, a 64 bit build might even want to include a second 32 bit binary.

Indeed, for compat binaries we'll probably want some sort of common pattern.
Unfortunately it's not as easy as building a second binary when CONFIG_COMPAT=y,
as some architectures have more than 2 supported ABIs. MIPS for example or x86_64
when counting x32.
Or maybe we can just pretend that those don't matter.
Something we can work on when the first series has been merged.

> So, I suppose
> one would ideally want the test to be in arch/x86/tests, with some way
> to pick up it up in arch/x86/um/tests.
> 
> Does this seem sensible in general?

It does.

> Benjamin

[0] https://git.kernel.org/pub/scm/linux/kernel/git/thomas.weissschuh/linux.git/commit/?h=kunit-kselftests-integration&id=14bf93f09eaa328a18e9190f46fa4ee697378617

> 
> Benjamin Berg (2):
>   tools/nolibc: add sigaction()
>   um: add a mcontext FP register handling test
> 
>  arch/x86/um/Makefile                     |   2 +
>  arch/x86/um/tests/Makefile               |  12 +++
>  arch/x86/um/tests/registers.c            |  22 +++++
>  arch/x86/um/tests/test-fp-save-restore.c | 118 +++++++++++++++++++++++
>  tools/include/nolibc/nolibc.h            |   3 +
>  tools/include/nolibc/signal.h            |  34 +++++++
>  6 files changed, 191 insertions(+)
>  create mode 100644 arch/x86/um/tests/Makefile
>  create mode 100644 arch/x86/um/tests/registers.c
>  create mode 100644 arch/x86/um/tests/test-fp-save-restore.c
> 
> -- 
> 2.50.0
>