Re: gdb support for SME-without-SVE ?

Peter Maydell via Gdb
2026-01-30T09:42:24Z

On Fri, 30 Jan 2026 at 04:28, Thiago Jung Bauermann
<thiago.bauermann@linaro.org> wrote:
>
> Peter Maydell <peter.maydell@linaro.org> writes:
>
> > On Thu, 29 Jan 2026 at 09:10, Peter Maydell <peter.maydell@linaro.org> wrote:
> >>
> >> On Thu, 29 Jan 2026 at 04:12, Thiago Jung Bauermann
> >> <thiago.bauermann@linaro.org> wrote:
> >> >
> >> > Peter Maydell <peter.maydell@linaro.org> writes:
> >> >
> >> > > On Wed, 28 Jan 2026 at 04:24, Thiago Jung Bauermann
> >> > > <thiago.bauermann@linaro.org> wrote:
> >> > >> I'm currently implementing SME-only (i.e. without SVE) support in GDB
> >> > >> for Linux userspace debugging. It's mostly done, I just need to test a
> >> > >> few things, polish the code and prepare the patches. I'm hoping to send
> >> > >> the patches next week.
> >> > >
> >> > > Let me know if a QEMU setup emulating "SME only" would be helpful
> >> > > for you with that.
> >> >
> >> > It would indeed! If there's a branch I can build, it would make my
> >> > testing quicker, and the regression testing more complete.
> >>
> >> I'll get one sorted out later today (the patches I have right now
> >> have a few issues I need to fix).
> >
> > This branch:
> >
> > https://gitlab.com/pm215/qemu/-/commits/sme-no-sve
>
> Thank you very much!
>
> > should let you create an SME-only CPU with "-cpu max,sve=off".
> > I have not given it much more than a very cursory testing, so
> > let me know if you run into any problems with it.
>
> Unfortunately I hit a kernel oops reliably when trying to run a GDB testcase:
>
> [ 156.387143] Internal error: Oops - Undefined instruction: 0000000002000000 [#1] SMP

> The same kernel and userspace binaries work fine in Arm FVP.

Thanks for testing -- this looks like it's going to be a QEMU
bug where we're accidentally making something UNDEF when it
should work when SME is present. I'll have a look at it.

-- PMM