Re: [PATCH] docs: Clarify gdb remote protocol AArch64 SVE and SME handling

[Peter Maydell <peter.maydell@linaro.org>]

On Fri, 20 Mar 2026 at 03:02, Thiago Jung Bauermann
<thiago.bauermann@linaro.org> wrote:
>
> Hello,
>
> Peter Maydell <peter.maydell@linaro.org> writes:
>
> > On Mon, 2 Feb 2026 at 23:41, Luis <luis.machado.foss@gmail.com> wrote:
> >>
> >> Hi,
> >>
> >>
> >> On 30/01/2026 09:36, Peter Maydell wrote:
> >> > On Thu, 29 Jan 2026 at 23:18, Luis <luis.machado.foss@gmail.com> wrote:
> >> >> I don't feel comfortable setting this is stone before we have a
> >> >> patch that clarifies how this separation between SVE and SME is
> >> >> achieved.
> >> >
> >> > I agree that we don't want to commit this until we're happy that
> >> > it's the right thing. This patch is my attempt to put down in a
> >> > concrete form how I think this should work.
> >> >
> >> > When you talk about "a patch that clarifies how this separation
> >> > between SVE and SME is achieved", what do you mean? A patch to
> >> > gdb? With this proposal, current gdb I think should work without
> >> > changes. The changes Thiago has are all because of the way that
> >> > the Linux ptrace API has chosen to represent SVE and SME, AIUI.
> >>
> >> We need a couple things from what I can see.
> >>
> >> First we need to teach gdb about SME without SVE, and that's what Thiago
> >> is working on. I´d like to see that patch first before we adjust the
> >> documentation for the SME-but-no-SVE mode. Just to make sure things match.
> >
> > Hi -- I just wanted to come back to this thread to ask how
> > the "native (ptrace) gdb SME-no-SVE" support is going. Do
> > we now have that landed, or at least solid enough that we are
> > happy to update the remote-protocol documentation?
>
> I was about to submit the patches when I ran the full GDB testsuite
> (I had been running a subset during development) and found a few
> regressions I need to fix. I don't expect big changes though, and
> I will submit the patches soon.
>
> The essence of the changes is that if the target has SME but not SVE,
> then GDB uses a target description with SVE but with vq = 1, meaning
> that the SVE register set has the same size as the FPSIMD regset.

How does it see the actual vector registers, then ? Those will
have a larger size than vq=1, but there is no separate place
to report them, at least in the remote protocol...

-- PMM