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 61EA447279F; Fri, 2 Oct 2026 09:28:06 +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=1790933290; cv=none; b=TGJZdGTRPd36kOxxNXimYH5Jvo843N2iLy97krw5kMj/M0FysZvl0WdWbBCAa+nkrpXRK38T1igpPA+EOtU4NFo/WYDHuRH8RCpKXSuT4k+zUdts9EKu9xRHCYdNf6Fxn5YEDy5r7lmxfUd2r0yecq+r6UgLqKeHpBloMpZd0KQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790933290; c=relaxed/simple; bh=ey+HfqbT063llCzkfHlDumf8iTEsGPYJdwUxMyASXx0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qstAiYhr7tkUXXu/qg7nH5AFTw0fVw+cuJMyeFDM8ncaTb2rMOFE73jQlcv9VcpB+bvcArpfQosMt+xjKwPUsiCp75l89+x4ZmVsr8F28wlTlzDos0+py9pIHUEdgwQLVqbTLvT3KKZD9SQEr619UoBFDiG/U0D63nPPbYoCjlE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b=JXF9aYC9; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="JXF9aYC9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 424F21F000FF; Fri, 2 Oct 2026 09:28:03 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=zx2c4.com header.i=@zx2c4.com header.a=rsa-sha256 header.s=20210105 header.b=JXF9aYC9 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1790933279; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dtcin0LGddrGq1z73zXhBfHbevxSulJDQC2ODA9S4LA=; b=JXF9aYC9WwUSK4dqsSbWZahQOF5tPs+qWfT6am7iM2kEiqJtJzCVxFzDeTv/m/a4MQVUpO GLRdB7QsZbpopzZdWvYR/SsEQbyfmCcXe2exUQZ5/eF4uZWlcciUWsy7qUj8Yd99apyea/ uqdi3Lw+wZdB/dnq0RpegAZySOW8XXE= Received: by mail.zx2c4.com (OpenSMTPD) with ESMTPSA id 0f473697 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Fri, 2 Oct 2026 09:27:58 +0000 (UTC) Date: Fri, 2 Oct 2026 11:27:54 +0200 From: "Jason A. Donenfeld" To: "Christophe Leroy (CS GROUP)" Cc: Nathan Chancellor , 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 Subject: Re: [PATCH v2] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data() Message-ID: References: <20260930133813.GA3142230@ax162> <20260930151337.GD3142230@ax162> <20261001102059.GA4176271@ax162> <83a874fb-db66-4dc2-8e14-68c7e28ae27c@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <83a874fb-db66-4dc2-8e14-68c7e28ae27c@kernel.org> On Fri, Oct 02, 2026 at 11:18:51AM +0200, Christophe Leroy (CS GROUP) wrote: > > > 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. No, that patch tested this option + actually calling builtin_memset. This new patch has the original code of zeroing a long at a time, but has the inline memset option to prevent future GCC from recognizing that pattern and making it outline. Codegen should be the same. Jason