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AJvYcCU5YqAPGuRyMxrmeB61CTep8UhEUuEMJOcaEn+8LmVe0mwICYfDWtC03i0ajo9WA5lH1k8=@sourceware.org X-Gm-Message-State: AOJu0Yx+14gdf7aw6glqPhXqyHaPG+HAwxwaaK5CK95UhPvrar7Ku9Rl phjl6xTAniVcotv9tvY6foNq+JpBScJOKki4nrG5yUTOJAYmX9bnF8seL6hUcWf/kJEtcIhrkRx FmfAbyzaa+yXA22hPN6Kc3n8w1ZFDXiI= X-Gm-Gg: AZuq6aKALVFj0HaP4XM71QFDPPZuXyKZ5kuHWUb7e8olCQ9dbNUgmdtLutd/mmoE3Yv jvYKDgWU/DlUaFg0drJU9a2w00GUJoCTaahxhpKA4+B/h9FxBC5Ml+8AYpYwME6xDnNPRcaf4hW MzBAHlqzl8nCqAIZUUa5x6ztLTOFmaMyZyH2e/ttgwqFL3JN9778kkinpTJlIrsXhLYMmPFDwEu tAwhRcCSCsk49gRbWNDInHcutSlLfPM6bPXY1SXo9kbCDnIVDTDu0YPsGx7V4OrvtfMLPg= X-Received: by 2002:a05:6830:ec4:b0:7ce:5139:301b with SMTP id 46e09a7af769-7d184c980acmr2078535a34.8.1769587381483; Wed, 28 Jan 2026 00:03:01 -0800 (PST) MIME-Version: 1.0 References: <87ldhigyao.fsf@linaro.org> In-Reply-To: <87ldhigyao.fsf@linaro.org> Date: Wed, 28 Jan 2026 08:02:53 +0000 X-Gm-Features: AZwV_Qhvi-2z-p5zZFdCW6n5IRKazbdK0OUJvfYz5aFWRYSBi6G-rP5OJcE6FUc Message-ID: Subject: Re: gdb support for SME-without-SVE ? To: Thiago Jung Bauermann Cc: Peter Maydell , gdb@sourceware.org, Manos Pitsidianakis Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.30 X-BeenThere: gdb@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Luis via Gdb Reply-To: Luis Errors-To: gdb-bounces~public-inbox=simark.ca@sourceware.org Sender: "Gdb" On Wed, Jan 28, 2026, 04:24 Thiago Jung Bauermann < thiago.bauermann@linaro.org> wrote: > Hello, > > 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. > Excellent. Thanks for the heads up. > Due to the limitations in the remote protocol that Luis mentioned below, > I can't run the tests against a remote target so I'm only focusing on > local debugging, unfortunately. > > Luis writes: > > > On Tue, Jan 27, 2026, 21:24 Peter Maydell > wrote: > > > > > (2) If the CPU has SME and not SVE, presumably we should still > > > expose org.gnu.gdb.aarch64.sve, as it's where the z registers are. > > > What should we report "vl" as here? How about when the CPU is not > > > in streaming mode and the z regs aren't accessible? > > > > Are there still Z registers without SVE? > > Yes, but they are only accessible while in streaming mode. > > For simplicity, if the inferior isn't in streaming mode I'm making the > SVE registers available in non-streaming mode (i.e., behave as if SVE is > supported) with vg = 2 as Peter mentions below. In this case, the Z > registers are equivalent to the regular vector registers. > > > I don't think this is properly supported in any case. On top of that > > SVE and SME are not properly supported via the remote protocol. In > > theory it works if you don't change vg/svg mid-execution. So no SSVE > > enabling etc. But in practice it does not work well. When the vg/svg > > size changes you end up with overruns or garbage. > > > > The initial implementation of SVE assumed remote debugging wasn't > > important. We're stuck with that until remote protocol enhancements > > are contributed. > > > > Those enhancements have been proposed multiple times but there were > > always downsides and it tends to die and fall into limbo. It mostly > > only affects SVE and SME. Maybe AMX. > > I'm planning to resume this work again in the next few months. Christina > and Klaus from Intel came up with a nice proposal. > Great. Hopefully we can get this restriction lifted and enable dynamic sizes for remote stubs. > -- > Thiago >