From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.7 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id E52377D2EF for ; Tue, 18 Jun 2019 13:32:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729249AbfFRNcc (ORCPT ); Tue, 18 Jun 2019 09:32:32 -0400 Received: from foss.arm.com ([217.140.110.172]:41266 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726088AbfFRNcc (ORCPT ); Tue, 18 Jun 2019 09:32:32 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2CBDA2B; Tue, 18 Jun 2019 06:32:31 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 956973F718; Tue, 18 Jun 2019 06:32:27 -0700 (PDT) Date: Tue, 18 Jun 2019 14:32:25 +0100 From: Dave Martin To: Peter Zijlstra Cc: Florian Weimer , Thomas Gleixner , Yu-cheng Yu , x86@kernel.org, "H. Peter Anvin" , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue Subject: Re: [PATCH v7 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file Message-ID: <20190618133223.GD2790@e103592.cambridge.arm.com> References: <87lfy9cq04.fsf@oldenburg2.str.redhat.com> <20190611114109.GN28398@e103592.cambridge.arm.com> <031bc55d8dcdcf4f031e6ff27c33fd52c61d33a5.camel@intel.com> <20190612093238.GQ28398@e103592.cambridge.arm.com> <87imt4jwpt.fsf@oldenburg2.str.redhat.com> <20190618091248.GB2790@e103592.cambridge.arm.com> <20190618124122.GH3419@hirez.programming.kicks-ass.net> <87ef3r9i2j.fsf@oldenburg2.str.redhat.com> <20190618125512.GJ3419@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190618125512.GJ3419@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, Jun 18, 2019 at 02:55:12PM +0200, Peter Zijlstra wrote: > On Tue, Jun 18, 2019 at 02:47:00PM +0200, Florian Weimer wrote: > > * Peter Zijlstra: > > > > > I'm not sure I read Thomas' comment like that. In my reading keeping the > > > PT_NOTE fallback is exactly one of those 'fly workarounds'. By not > > > supporting PT_NOTE only the 'fine' people already shit^Hpping this out > > > of tree are affected, and we don't have to care about them at all. > > > > Just to be clear here: There was an ABI document that required PT_NOTE > > parsing. > > URGH. > > > The Linux kernel does *not* define the x86-64 ABI, it only > > implements it. The authoritative source should be the ABI document. > > > > In this particularly case, so far anyone implementing this ABI extension > > tried to provide value by changing it, sometimes successfully. Which > > makes me wonder why we even bother to mainatain ABI documentation. The > > kernel is just very late to the party. > > How can the kernel be late to the party if all of this is spinning > wheels without kernel support? PT_GNU_PROPERTY is mentioned and allocated a p_type value in hjl's spec [1], but otherwise seems underspecified. In particular, it's not clear whether a PT_GNU_PROPERTY phdr _must_ be emitted for NT_GNU_PROPERTY_TYPE_0. While it seems a no-brainer to emit it, RHEL's linker already doesn't IIUC, and there are binaries in the wild. Maybe this phdr type is a late addition -- I haven't attempted to dig through the history. For arm64 we don't have this out-of-tree legacy to support, so we can avoid exhausitvely searching for the note: no PT_GNU_PROPERTY -> no note. So, can we do the same for x86, forcing RHEL to carry some code out of tree to support their legacy binaries? Or do we accept that there is already a de facto ABI and try to be compatible with it? >From my side, I want to avoid duplication between x86 and arm64, and keep unneeded complexity out of the ELF loader where possible. Cheers ---Dave [1] https://github.com/hjl-tools/linux-abi/wiki/Linux-Extensions-to-gABI