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[81.2.115.145]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-482dac1113csm707385e9.4.2026.01.29.10.11.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Jan 2026 10:11:22 -0800 (PST) From: Peter Maydell To: gdb-patches@sourceware.org Cc: Thiago Jung Bauermann , Luis , Manos Pitsidianakis Subject: [PATCH] docs: Clarify gdb remote protocol AArch64 SVE and SME handling Date: Thu, 29 Jan 2026 18:11:21 +0000 Message-ID: <20260129181122.1426596-1-peter.maydell@linaro.org> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org The documentation of the AArch64 target features for the gdb remote protocol has some areas where it is unclear about SVE and SME: * it doesn't say what to do if the target has only SME * it isn't clear about what the org.gnu.gdb.aarch64.sve vector register size should be when both SME and SVE are present Clarify/correct the documentation: * org.gnu.gdb.aarch64.sve is effectively "the feature for the z vector registers", and must be provided even when the target only implements SME (because the z registers exist in an SME only CPU) * the z register size and the 'vg' pseudoregister in org.gnu.gdb.aarch64.sve follow the architectural "effective SVE vector length", which might be either the non-streaming SVE vector length or the streaming SVE vector length Reviewed-by: Thiago Jung Bauermann --- gdb/doc/gdb.texinfo | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo index 80f49e21b7e..711a45435ef 100644 --- a/gdb/doc/gdb.texinfo +++ b/gdb/doc/gdb.texinfo @@ -49742,7 +49742,8 @@ Extra registers are allowed in this feature, but they will not affect @subsubsection AArch64 SVE registers feature The @samp{org.gnu.gdb.aarch64.sve} feature is optional. If present, -it means the target supports the Scalable Vector Extension and must contain +it means the target supports either the Scalable Vector Extension (SVE) or +the Scalable Matrix Extension (SME) and must contain the following registers: @itemize @minus @@ -49780,6 +49781,14 @@ vector registers from the @samp{org.gnu.gdb.aarch64.fpu} feature. The first 128 bits of the @samp{z} registers overlap the 128 bits of the @samp{v} registers, so changing one will trigger a change to the other. +@samp{vg} represents the size of the @samp{z} registers, and is what +the Arm architecture defines as the ``Effective SVE vector length''. That +means that if the target implements SME and is in streaming vector mode, +it is the streaming vector length. If the target implements only SME and +not SVE, and is not in streaming vector mode, then @samp{vg} is 2 +(indicating 128-bit vectors) and the @samp{z} registers match the @samp{v} +FPU registers. + For the types of the @samp{z}, @samp{p} and @samp{ffr} registers, please check the aarch64-sve.c file. No XML file is available for this feature because it is dynamically generated based on the current vector length. @@ -49793,6 +49802,9 @@ aarch64-sve.c file, and should match what is described in aarch64-fpu.xml. Extra registers are allowed in this feature, but they will not affect @value{GDBN}. +The @samp{org.gnu.gdb.aarch64.sve} feature is required when the target also +reports support for the @samp{org.gnu.gdb.aarch64.sme} feature. + @subsubsection AArch64 Pointer Authentication registers feature The @samp{org.gnu.gdb.aarch64.pauth} optional feature was introduced so @@ -49948,6 +49960,10 @@ extensions of the architecture. Extra registers are allowed in this feature, but they will not affect @value{GDBN}. +Note that a target with only SME but not SVE support must still +provide the @samp{org.gnu.gdb.aarch64.sve} feature, to expose the +@samp{z} vector registers. + The @samp{org.gnu.gdb.aarch64.sme} feature is required when the target also reports support for the @samp{org.gnu.gdb.aarch64.sme2} feature. -- 2.43.0