From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 725DF470456; Fri, 2 Oct 2026 09:18:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790932739; cv=none; b=XyeOzRTZSe2inKlrdAJF1DdsjW6RDfIOsBbnWaSb4rZYhovW/akuXwa6Ll5I6ZQtHBQQm0oW5kIiPbMPqP9jt6GcN82yNFQtl+Rj53U4zxRNAIr3grvcOJZUBp2JNlRUjvCBhPls+D6Rmj7FPei57GH/nXq4XTmwTw1A8Tov65A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790932739; c=relaxed/simple; bh=suekEUMK13TAHHU4Cf2etsAqCGbQmsK5+r24aKbCtI4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gyByd98LZHdwDb6yM2MrFJwcm9PJUiDVZsrU908X7ViUQWMyxZfdRr5PIEjjk7rMgJerBhNFbKJc5wIeqjHMlCE3OSaiuMgXSvQXk1KgjfDXNJCF76xSPbVMHYYE6CtO/dcD6sgK+ZCiQtRRsk/K8RkjfpFWvfNGI8agl+ESMxw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Bib7a0PM; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Bib7a0PM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 854CD1F000FF; Fri, 2 Oct 2026 09:18:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790932738; bh=kUPal21B/mSeq/i2I0fVbafYDiAiPgFaWqso5GBNYgw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Bib7a0PM9uB/Juf5Fvu+oSR5+RsFmNc22FbQ3W8GIqtnemb+ACt71CTBw2sib4s92 fFnF4433pDjiEGcg7x5zAEvURZ47Q+qrMo2IYrA95mk7vxbQjDv/9+rywF+rGaZ2P7 MWKHtnnqTQ8pjgpyCRbNP4t/CulAsggec5uV/Q4dsuX2d3LyZTJU72PUMvHEvpTwms bQHF6mNjpQkROI+pb8cwG0OWRm4RbVW2IZfgTwGPNyr7ZCIRlyeoMH50oI1zzLRcfH fUDv5QFMQ3ZAiDD1vUKWIdfRDKrY3rzo4o2Sj1ojPFTeN/KT1OBRSYQl++2ya2NmOw blTAYWLPs3B3Q== Message-ID: <83a874fb-db66-4dc2-8e14-68c7e28ae27c@kernel.org> Date: Fri, 2 Oct 2026 11:18:51 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data() To: "Jason A. Donenfeld" , Nathan Chancellor Cc: Nick Desaulniers , Andy Lutomirski , Thomas Gleixner , Theodore Ts'o , Vincenzo Frascino , Bill Wendling , Justin Stitt , Catalin Marinas , Will Deacon , Mark Rutland , Huacai Chen , WANG Xuerui , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, llvm@lists.linux.dev References: <20260930133813.GA3142230@ax162> <20260930151337.GD3142230@ax162> <20261001102059.GA4176271@ax162> Content-Language: fr-FR From: "Christophe Leroy (CS GROUP)" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Le 01/10/2026 à 12:48, Jason A. Donenfeld a écrit : > On Thu, Oct 01, 2026 at 12:20:59PM +0200, Nathan Chancellor wrote: >> control. The change that introduced -max-store-memset only did it to >> "allow fine-tuning of the inlining threshold for performance analysis >> and optimization". If they decide to remove it for whatever reason, >> we're back to square one. > > I suppose all the more reason to get -finline-stringops=memset added to > clang. Then the dual-default thing you came up with below will naturally > start choosing the first option when it becomes available. > >> I know something like below would be uglier due to the ifdef but it >> would avoid changing anything for GCC while clearing up the issue at >> hand for clang in a guaranteed stable and succinct manner. > > But then we're back to the byte-by-byte codegen that Christophe pointed > out. > >> If that is not acceptable, something like the following does appear to >> work for me. > > Okay, great, let's do that. > > Does this commit seem okay with you? I used the diff you sent below and > adjusted the commit message: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.zx2c4.com%2Flinux-rng%2Fcommit%2F%3Fid%3D56ff95ee85715047eb5b5220243778af657778c8&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cd89b4de22ff94b6be71208df1fa9839a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639264485055490029%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=Vxf8xRCdLavtw4Dmi%2B49FY1lJDWtm%2BjKv7f8BxKTGq4%3D&reserved=0 > The commit message says: Similarly, GCC has -finline-stringops=memset to do the same [4], should this issue ever hit future version of GCC. Why default "-finline-stringops=memset" if $(cc-option,-finline-stringops=memset), have we identified cases where build fail without that or is it just for future provision ? As shown in my previous email, with GCC 16 on powerpc32 we get a slightly better code without this option. --- diff --git a/init/Kconfig b/init/Kconfig index 8583d9f06c52..98d8d7fa64c5 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -173,6 +173,11 @@ config CC_HAS_ALLOC_TOKEN config CC_HAS_MULTIDIMENSIONAL_NONSTRING def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) = { };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror) +config CC_OPT_INLINE_MEMSET + string + default "-finline-stringops=memset" if $(cc-option,-finline-stringops=memset) + default "-mllvm -max-store-memset=4294967295" if $(cc-option,-mllvm -max-store-memset=4294967295) + config LD_CAN_USE_KEEP_IN_OVERLAY # ld.lld prior to 21.0.0 did not support KEEP within an overlay description # https://github.com/llvm/llvm-project/pull/130661