[RESEND PATCH] selftests/pidfd: align stack to fix SP alignment exception

[Will Deacon]

On Fri, Jul 18, 2025 at 03:10:32PM -0600, Shuah Khan wrote:
> Can you take a look at this and let me know if this change looks
> good to you both.
> 
> I can take this through my tree after your reviews.

I never got to the point of fully understanding how the test was
supposed to work, but it is true that arm64 requires a 16-byte aligned
stack pointer and this patch appears to achieve that.

Will