From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2FAB9CA5FC5 for ; Wed, 30 Sep 2026 13:38:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Ig13N2tfIjFRsSeqDuP4ixyXHADT+oxuPpwsFpsBiHk=; b=n8BUo0i9LYE0gvUIaY8qLd3Iw6 BP4ktvj8r27Z74fscZqjm2LVGrR375V3/IC99sYKXG+BD3qHJbTe/smkHBeolYQTta0XrAEbIvsI7 siuqMgXElLYdMhocb2ZW9dbcBdxGChPpH2ezJ7ejizFZv6mYnuVW8Mf6g2bt+LjDZof8l6uNqAeGW JMF335WD6mQpQ0VXaWFLvJz8Tc9+XYIXcmjZmMNylbxt1NZqUepGh/iVa4Yr+YSFsUut6afRnW9so sHZp73rCyNgMFahUqeqdolPI/xOWbV9uW9K1hz64PO1sELwc8CnnI7vBLAtkqm9Jm04hMK28yqtwN v40qTuDw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xBuVz-000000069Zy-1tsw; Wed, 30 Sep 2026 13:38:31 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xBuVs-000000069YN-0esx; Wed, 30 Sep 2026 13:38:25 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 3D5BC6025A; Wed, 30 Sep 2026 13:38:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBD6B1F000FF; Wed, 30 Sep 2026 13:38:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790775502; bh=Ig13N2tfIjFRsSeqDuP4ixyXHADT+oxuPpwsFpsBiHk=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=f+lk879yO1tcwpxTCZ8Vu9BSZUmqzoN86ot1Geu5VLUsqPRG9EiYd59TtYmDI/DQx b8PpR9XUHRj0fTYkMmqXQuU21rsM9TF4RTV+0y9feymcUMVNsiCzbuBPKCg7LcBInO A8qletS7Fjls0KgPrzllrFG2yFr3jSqVabH3BfItoBP22iHLl1D1M+B10unFPxeYbS DoBEprp5b4czipy9XTDOYyQwloYcLFKkBr+bQORPpJFN8w65Cv7oGrANxZ7mpBtWFH X/3FQ1hd+ZdBx+IV0FxW43+cOBuEql4F0qrdZWn1SclMvfp5mjwnEyjv/+mEW0gQs2 c0/P6Q0/ruZRw== Date: Wed, 30 Sep 2026 15:38:13 +0200 From: Nathan Chancellor To: Nick Desaulniers Cc: "Jason A. Donenfeld" , "Christophe Leroy (CS GROUP)" , 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: <20260930133813.GA3142230@ax162> References: <20260925-vdso-getrandom-avoid-memset-llvm-24-v2-1-ce640f872393@kernel.org> <9d1c338b-368f-4ea2-a12e-c28d49adff5e@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Sep 29, 2026 at 11:24:11AM -0700, Nick Desaulniers wrote: > arch/arm64/kvm/hyp/nvhe/Makefile has this pattern for exactly the same > problem I suspect. Maybe that's the right tool in the toolbox? > > ``` > diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile > index 8dbf2532a573..27fa72d8fb86 100644 > --- a/arch/riscv/kernel/vdso/Makefile > +++ b/arch/riscv/kernel/vdso/Makefile > @@ -27,7 +27,7 @@ asflags-y += -DVDSO_CFI=1 > endif > > # Files to link into the vdso > -obj-vdso = $(patsubst %, %.o, $(vdso-syms)) note.o > +obj-vdso = $(patsubst %, %.o, $(vdso-syms)) note.o ../../lib/memset.o > > ifdef CONFIG_VDSO_GETRANDOM > obj-vdso += vgetrandom-chacha.o > ``` > Fixes `make -skj"$(nproc)" ARCH=riscv LLVM=1 mrproper allmodconfig > vdso_prepare` for me, as per For the record, this also happens with the 32-bit PowerPC vDSO, as I noted in the commit message of v2. I should update the issue too, I only realized this after wider testing. So if this is the route we want to go, we would need a memset() for that vDSO as well. > https://github.com/ClangBuiltLinux/linux/issues/2183 > (Nathan, don't forget to link to that in the commit message) Yes, thanks, I have added it for v3. > I'm surprised I didn't need -fno-semantic-interposition (or one of the > related flags... -fvisibility=hidden) > > If we want to get better, (if performance matters here and we want to > trade source+build system complexity for absolute code perf) I would > start with that, then worry about clawing back performance via things > like: > - __builtin_memset_inline > - -finline-stringops=memset > - -ffunction-sections+-Wl,--gc-sections to dead code eliminate the out > of line copy of memset, though IIRC there's potential for wasted space > due to alignment requirements (maybe the out of line copy of memset is > smaller...idk) Yeah, I guess it is ultimately up to the maintainers what route they prefer. -- Cheers, Nathan