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Mon, 21 Jul 2025 07:54:26 -0700 (PDT) Received: from localhost ([2a02:8308:a00c:e200:25d5:2321:c8db:1609]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3b61ca5c8c9sm10755685f8f.85.2025.07.21.07.54.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Jul 2025 07:54:25 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 21 Jul 2025 16:54:25 +0200 Message-Id: Subject: Re: [PATCH] riscv: Add sysctl to control discard of vstate during syscall Cc: "linux-riscv" To: "Drew Fustini" , "Palmer Dabbelt" , =?utf-8?q?Bj=C3=B6rn_T=C3=B6pel?= , "Alexandre Ghiti" , "Paul Walmsley" , "Samuel Holland" , "Drew Fustini" , "Andy Chiu" , "Conor Dooley" , , From: =?utf-8?q?Radim_Kr=C4=8Dm=C3=A1=C5=99?= References: <20250719033912.1313955-1-fustini@kernel.org> In-Reply-To: 2025-07-21T14:35:38+02:00, Radim Kr=C4=8Dm=C3=A1=C5=99 : > Shouldn't the RISC-V Linux syscall ABI be defined somewhere? To clarify this point. My issue is with the following part in Documentation/arch/riscv/vector.rst: >> As indicated by version 1.0 of the V extension [1], vector registers ar= e >> clobbered by system calls. >> [...] >> 1: https://github.com/riscv/riscv-v-spec/blob/master/calling-convention= .adoc The ISA does not say that vector registers are clobbered by system calls. All the ISA says is: "This Appendix is only a placeholder to help explain the conventions used in the code examples, and is not considered frozen or part of the ratification process. The official RISC-V psABI document is being expanded to specify the vector calling conventions." while the RISC-V psABI says: "The calling convention for system calls does not fall within the scope of this document. Please refer to the documentation of the RISC-V execution environment interface (e.g OS kernel ABI, SBI)." We made a circular dependency, misinterpreted the ISA, and probably implemented a suboptimal syscall ABI -- preserving vector registers seems strictly better. > How come we could have broken it with 9657e9b7d253? We changed the ABI once, so maybe we can change it back? Thanks.