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 6753B4FC8CD; Wed, 30 Sep 2026 13:38:25 +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=1790775515; cv=none; b=Mm5Bt3fjQYJW28CBHvF+jFZj2JenQ/2t29XaPOkTziYOgS2g6ebLLvL1LGvB28wCrTk0N4Xr9e09KRDWuEiGXT9kplZj5/OP77Zm9xnKNEogHOHCXQWoB3GTJtfpVgzMGg18t0XLLbpgKR6gI+4Aniwh7MDQM/osuYZB6jA/nIc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790775515; c=relaxed/simple; bh=Z/y/h04Kuor6b1R5DzL4Dbxlj9a2OKgjlPvSGbDTUxE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=oiRY/QAAbRUAyL11LboFX7535LxtYg2+v0mHZOvcEKSb4xHCHkRKcazrv3Zr7adukrqlVbY2X/OxrWQMeyNoZf1N0u1u5my2BKkHEviMGkG5tbr2618mbaqKNmFRAMTH/P8Gz9cpQhxjUd/wGXJUe8oJ3F7+0FZETNgrI4QUQ70= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=f+lk879y; 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="f+lk879y" 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> 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=us-ascii Content-Disposition: inline In-Reply-To: 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