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[63.157.97.90]) by smtp.gmail.com with ESMTPSA id y12-20020aa78f2c000000b00581dd94be3asm9023586pfr.61.2023.01.10.21.23.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Jan 2023 21:23:30 -0800 (PST) Message-ID: Date: Tue, 10 Jan 2023 21:23:26 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: Auto-enabling V unit and/or use of elf attributes (was Re: Adding V-ext regs to signal context w/o expanding kernel struct sigcontext to avoid glibc ABI break) Content-Language: en-US To: Vineet Gupta , Kito Cheng Cc: Philipp Tomsich , Andy Chiu , Vincent Chen , Florian Weimer , Rich Felker , Andrew Waterman , Palmer Dabbelt , =?UTF-8?Q?Christoph_M=c3=bcllner?= , davidlt@rivosinc.com, Arnd Bergmann , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Szabolcs Nagy , Greentime Hu , Aaron Durbin , Andrew de los Reyes , linux-riscv , GNU C Library References: <1631497278-29829-1-git-send-email-vincent.chen@sifive.com> <7430f494-9b43-5e03-c1e9-6b83e2611a11@rivosinc.com> <91ef3c45-165f-d2b3-7c77-322c01802c41@rivosinc.com> <18465ca3-934f-5b3e-170c-1ff0edea3a89@rivosinc.com> <1f8f1d21-4a19-54fe-8b29-bf9e2a8501d7@rivosinc.com> <3a838afe-974b-60bb-a0e5-83e366ec652e@rivosinc.com> <3923eeee-e4dc-0911-40bf-84c34aee962d@linaro.org> In-Reply-To: <3923eeee-e4dc-0911-40bf-84c34aee962d@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Richard Henderson via Libc-alpha Reply-To: Richard Henderson Errors-To: libc-alpha-bounces+e=80x24.org@sourceware.org Sender: "Libc-alpha" On 1/10/23 17:22, Richard Henderson wrote: > And, surely, there's some minimal vector configuration for which the allocation must succeed. To answer my own question here, no, there does not seem to be a way to cap VLMAX in the OS or the hypervisor -- vsetvli rd, r0, e8 will always set VL to the VLMAX for which the cpu is configured. (ARM SVE can artificially limit the vector length. Linux chooses the default vector length so that state fits within the existing 4k signal stack frame. This is good enough for the vector usage within e.g. strlen. In order to take advantage of any larger vector length the hardware may support, one must use a prctl.) r~