Re: gdb support for SME-without-SVE ?

[Peter Maydell via Gdb <gdb@sourceware.org>]

On Tue, 27 Jan 2026 at 14:21, Simon Marchi <simark@simark.ca> wrote:
>
>
>
> On 2026-01-27 06:31, Peter Maydell via Gdb wrote:
> > Hi: is GDB for Arm intended to support configurations where the target
> > CPU has SME but not SVE?
> >
> > We're just implementing support for that in QEMU for using SME
> > with the hvf hypervisor accelerator on macos systems, but when
> > we tried connecting gdb to QEMU gdb crashed:
> >
> >   (gdb) target remote localhost:1234
> >   Remote debugging using localhost:1234
> >   ../../gdb/aarch64-tdep.c:3068: internal-error:
> > aarch64_pseudo_register_type: bad register number 160
> >   A problem internal to GDB has been detected,
> >   further debugging may prove unreliable.
> >   Fatal signal: Abort trap: 6
> >
> > https://lore.kernel.org/qemu-devel/CAAjaMXZLG2aBtStRhyvmdENj1Z+Mx05BmDgyYUoYrc_ZnHwyVQ@mail.gmail.com/
> >
> > Is this a known missing feature in GDB, or is it a config that's
> > supposed to work but we've got the XML register description wrong
> > somehow?
> >
> > It looks from the aarch64-tdep.c code like perhaps GDB assumes
> > that the Vn vector registers only exist with SVE, but they also
> > exist in SME-only CPUs.
>
> Not an ARM expert, but from what I read, SME builds on top of SVE, so I
> would guess that having SME implies having SVE.

No, it does not imply it. SVE plus SME is a very common config,
but the Apple M4 chip has SME without SVE.

-- PMM