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

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

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.

-- 
Thiago