Why is the kernel getting into the undefined instruction handler? It should only use VFP instructions from within a specific section marked by the fpu_kern_* functions

allanjude added reviewers: markj, Klara.Sep 6 2023, 3:34 PM

In D41759#951401, @andrew wrote:

Why is the kernel getting into the undefined instruction handler? It should only use VFP instructions from within a specific section marked by the fpu_kern_* functions

As I understand it, your comment is only true when fpu_kern_enter() is called with FPU_KERN_NOCTX. When an explicit context is provided, I believe the intent is to enable VFP lazily, but that is currently broken. The intent of the patch is to fix fpu_kern_enter() to behave properly when the caller supplies a context.

sys/arm/arm/vfp.c
281	This addition is unrelated to the rest of the patch and should be added separately.

des added a subscriber: des.Nov 7 2023, 7:07 PM

des added inline comments.

sys/arm/arm/undefined.c
354

https://reviews.freebsd.org/D42969 and the rest of the patch series are available for review. They break up this patch into logical commits, plus ensure that we do not erroneously consume an exception if a kernel thread triggers a VFP exception without having entered an FPU section. This lets fpu_kern_enter() work on ARM when a FPU context is supplied by the caller.

allanjude commandeered this revision.Dec 11 2023, 4:19 PM

allanjude abandoned this revision.

allanjude added a reviewer: alex.stetsenko_gmail.com.