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 A17804D0CEB; Wed, 30 Sep 2026 14:21:33 +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=1790778102; cv=none; b=TEYUvW71P78StC3E2E96eo+jXy5p6rWa2WX3LSqhGW50bHY5wkjXxjEXlyLkCG4AcXugFSYPqlC4XGDpRgaFevxytTwfdaeinDPIU8btDfVvXEwT8r2w3tzPgemQKtZYKGv456D20TcvU96eA14az5U2W+h+p4Wht51Apdn8tp0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790778102; c=relaxed/simple; bh=kPxdLIHgctd4mGb5ljs1Z0kF/Hg2+/RBCFtsiT4urG0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Vwyf/CLUKxtJtFmseJz4+aVqtAF+hFkA7AmB6FEZkn1LXz5yBzi6489Jm60OD+KFb7jPedwx7cdUyylRn2G3vHqtOK3f42A8AQ8/H+YKo1MiRzjymbv2qOIu+Bx7mlrnIw28M/97qsr9xVuGik82peRwsJHS9c2bDsktxjCdgVg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b=kkRK91cQ; 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="kkRK91cQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2F7A1F00893; Wed, 30 Sep 2026 14:21:28 +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=kkRK91cQ DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1790778087; 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: in-reply-to:in-reply-to:references:references; bh=zcThwgFUB4BfR5xfqdh6THtQYRaz9GGWFb0MJecCduw=; b=kkRK91cQzj+9vwUYtmGxpP6XHVefTkbHAXdd3nIiFVR+tOEuf0OaDl9hKkY9dgnZA+uIja kvvsMMlW1aun0HmpF4USkn2HKIB/ExvhSKaoIDBa5/FJ8DgYeE/zmuK/55JeWGBQCXPp3h CRPitXuJosLH57qy20oRmbXytVm4JwY= Received: by mail.zx2c4.com (OpenSMTPD) with ESMTPSA id de3a0bd1 (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Wed, 30 Sep 2026 14:21:26 +0000 (UTC) Date: Wed, 30 Sep 2026 16:21:21 +0200 From: "Jason A. Donenfeld" To: Nathan Chancellor Cc: Nick Desaulniers , "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: References: <20260925-vdso-getrandom-avoid-memset-llvm-24-v2-1-ce640f872393@kernel.org> <9d1c338b-368f-4ea2-a12e-c28d49adff5e@kernel.org> <20260930133813.GA3142230@ax162> 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 In-Reply-To: <20260930133813.GA3142230@ax162> On Wed, Sep 30, 2026 at 03:38:13PM +0200, Nathan Chancellor wrote: > 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. I think linking in an out-of-line memset.o is not appealing. This isn't a general library or something. So let's just go with your v2 approach, fixed up in the ways we mentioned.