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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-427f009a781sm20879873f8f.30.2025.10.21.06.48.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Oct 2025 06:48:05 -0700 (PDT) Date: Tue, 21 Oct 2025 14:48:03 +0100 From: David Laight To: Borislav Petkov Cc: Sohil Mehta , x86@kernel.org, Dave Hansen , Thomas Gleixner , Ingo Molnar , Jonathan Corbet , "H . Peter Anvin" , Andy Lutomirski , Josh Poimboeuf , Peter Zijlstra , Ard Biesheuvel , "Kirill A . Shutemov" , Xin Li , David Woodhouse , Sean Christopherson , Rick Edgecombe , Vegard Nossum , Andrew Cooper , Randy Dunlap , Geert Uytterhoeven , Kees Cook , Tony Luck , Alexander Shishkin , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org Subject: Re: [PATCH v10 02/15] x86/asm: Introduce inline memcpy and memset Message-ID: <20251021144803.519e6244@pumpkin> In-Reply-To: <20251021124751.GLaPeA9z8BCIe8AudC@fat_crate.local> References: <20251007065119.148605-1-sohil.mehta@intel.com> <20251007065119.148605-3-sohil.mehta@intel.com> <20251021124751.GLaPeA9z8BCIe8AudC@fat_crate.local> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 21 Oct 2025 14:47:51 +0200 Borislav Petkov wrote: > On Mon, Oct 06, 2025 at 11:51:06PM -0700, Sohil Mehta wrote: > > From: "Peter Zijlstra (Intel)" > > > > Provide inline memcpy and memset functions that can be used instead of > > the GCC builtins when necessary. The immediate use case is for the text > > poking functions to avoid the standard memcpy()/memset() calls within an > > RFLAGS.AC=1 context. > > ... because objtool does not allow function calls with AC=1 because... see > objtool/Documentation/objtool.txt, warning type 9, yadda yadda... > But for the purpose of code patching they don't need to be 'rep movsb'. An inline function with a C byte copy loop is fine - provided you do something to stop gcc pessimising it. Obvious options are a volatile pointer (or READ_ONCE()) or a barrier(). David