Re: gdb support for SME-without-SVE ?

Peter Maydell via Gdb
2026-01-30T18:34:53Z

On Fri, 30 Jan 2026 at 18:18, Thiago Jung Bauermann
<thiago.bauermann@linaro.org> wrote:
> Peter Maydell <peter.maydell@linaro.org> writes:
> > With my updated QEMU
> > (which you can find in the new "sme-no-sve-2" in my gitlab repo)
> > that can now run the tests without making the kernel fall over.
> > It reports:
> >
> > # of expected passes 241
> > # of unexpected failures 37
> >
> > Is that the same as you see on the fast model, or does this
> > indicate that I still have more QEMU bugs to track down?
> > (Peeking into gdb.log, these failures seem to be run-on
> > failures from the program under test getting a SIGILL
> > in initialize_zt_state(), so my guess is QEMU is still not
> > quite right.)
>
> Indeed, there seems to be something off with QEMU.
> On FVP, all the tests pass:
>
> === gdb Summary ===
>
> # of expected passes 278

Just to check, does your FVP have the SME2p1 feature ?
(Should show up as "sme2p1" in the feature list in /proc/cpuinfo
in the guest.) The SIGILL is happening on the attempt to set ZT0:

/* Initialize ZT0. */
/* ldr zt0, x0 */
__asm __volatile (".word 0xe11f8000");

because QEMU thinks that EL0 doesn't have access to ZT0.
If your FVP isn't emulating SME2p1 then the test code will
return early before getting to that part of the function.

-- PMM