From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Martin Subject: Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations Date: Wed, 16 May 2018 16:49:59 +0100 Message-ID: <20180516154957.GT7753@e103592.cambridge.arm.com> References: <1526480447-18185-1-git-send-email-Dave.Martin@arm.com> <20180516152913.GY1392@brightrain.aerifal.cx> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180516152913.GY1392@brightrain.aerifal.cx> Sender: linux-kernel-owner@vger.kernel.org To: Rich Felker Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Richard Henderson , Ivan Kokshaysky , Matt Turner , Russell King , Catalin Marinas , Will Deacon , Tony Luck , Fenghua Yu , Michal Simek , Ralf Baechle , James Hogan , Greentime Hu , Vincent Chen , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Palmer Dabbelt , Albert List-Id: linux-arch.vger.kernel.org On Wed, May 16, 2018 at 11:29:13AM -0400, Rich Felker wrote: > On Wed, May 16, 2018 at 03:20:47PM +0100, Dave Martin wrote: > > There are constraints on defining AT_* auxvec tags that are not > > obvious to the casual maintainer of either the global > > or the arch-specific headers. This is likely > > to lead to mistakes. (I certainly fell foul of it...) > > > > For the benefit of future maintainers, this patch collects the > > relevant information in one place, documenting how the namespace > > needs to be managed, and noting all the values currently in use. > > > > Maintaining a global list may result in some merge conflicts, but > > AT_* values are not added frequently. I'm open to suggestions on > > the best approach. > > > > I also assume that values 38 and 39 may have been used for > > historical purposes, such as an architecture that is no longer > > supported. If they have definitely never been used for anything, > > they could be removed from the "reserved" list. > > On the userspace side (elf.h) all the AT_* constants are in one file. > Why don't we just do the same here and eliminate the > arch/*/include/uapi/asm/auxvec.h files and likewise the need to > manually maintain consistency of the comments about reservations? > > If there are reasons not to do that, I'm not opposed to this patch > as-is. I agree, it would be better to merge them. My concern was that the correct way to get these definitions from userspace is very unclear, so there may be software out there including directly, which would now lack expected definitions. codesearch.debian.net shows no real hits for that, so maybe I'm too paranoid. Since only contains #defines, it may be enough for arch headers to include . Thoughts? Cheers ---Dave From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:50790 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750746AbeEPPuI (ORCPT ); Wed, 16 May 2018 11:50:08 -0400 Date: Wed, 16 May 2018 16:49:59 +0100 From: Dave Martin Subject: Re: [RFC PATCH] UAPI: Document auxvec AT_* namespace policy and note reservations Message-ID: <20180516154957.GT7753@e103592.cambridge.arm.com> References: <1526480447-18185-1-git-send-email-Dave.Martin@arm.com> <20180516152913.GY1392@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180516152913.GY1392@brightrain.aerifal.cx> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Rich Felker Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Richard Henderson , Ivan Kokshaysky , Matt Turner , Russell King , Catalin Marinas , Will Deacon , Tony Luck , Fenghua Yu , Michal Simek , Ralf Baechle , James Hogan , Greentime Hu , Vincent Chen , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Palmer Dabbelt , Albert Ou , Martin Schwidefsky , Heiko Carstens , Yoshinori Sato , "David S. Miller" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Chris Zankel , Max Filippov Message-ID: <20180516154959.CIN9RMXyp8F-OF19ew1b7CfDenb_8pUPLxEAJe6oCo4@z> On Wed, May 16, 2018 at 11:29:13AM -0400, Rich Felker wrote: > On Wed, May 16, 2018 at 03:20:47PM +0100, Dave Martin wrote: > > There are constraints on defining AT_* auxvec tags that are not > > obvious to the casual maintainer of either the global > > or the arch-specific headers. This is likely > > to lead to mistakes. (I certainly fell foul of it...) > > > > For the benefit of future maintainers, this patch collects the > > relevant information in one place, documenting how the namespace > > needs to be managed, and noting all the values currently in use. > > > > Maintaining a global list may result in some merge conflicts, but > > AT_* values are not added frequently. I'm open to suggestions on > > the best approach. > > > > I also assume that values 38 and 39 may have been used for > > historical purposes, such as an architecture that is no longer > > supported. If they have definitely never been used for anything, > > they could be removed from the "reserved" list. > > On the userspace side (elf.h) all the AT_* constants are in one file. > Why don't we just do the same here and eliminate the > arch/*/include/uapi/asm/auxvec.h files and likewise the need to > manually maintain consistency of the comments about reservations? > > If there are reasons not to do that, I'm not opposed to this patch > as-is. I agree, it would be better to merge them. My concern was that the correct way to get these definitions from userspace is very unclear, so there may be software out there including directly, which would now lack expected definitions. codesearch.debian.net shows no real hits for that, so maybe I'm too paranoid. Since only contains #defines, it may be enough for arch headers to include . Thoughts? Cheers ---Dave