From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 72937 invoked by alias); 22 Dec 2016 01:40:16 -0000 Mailing-List: contact binutils-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: binutils-owner@sourceware.org Received: (qmail 72916 invoked by uid 89); 22 Dec 2016 01:40:15 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-4.8 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_NONE,RP_MATCHES_RCVD,SPF_PASS autolearn=ham version=3.3.2 spammy=realised, veto, reserved X-Spam-User: qpsmtpd, 2 recipients X-HELO: mailapp01.imgtec.com Received: from mailapp01.imgtec.com (HELO mailapp01.imgtec.com) (195.59.15.196) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 22 Dec 2016 01:40:14 +0000 Received: from HHMAIL01.hh.imgtec.org (unknown [10.100.10.19]) by Forcepoint Email with ESMTPS id 1196FD02CFEA3; Thu, 22 Dec 2016 01:40:10 +0000 (GMT) Received: from [10.20.78.42] (10.20.78.42) by HHMAIL01.hh.imgtec.org (10.100.10.21) with Microsoft SMTP Server id 14.3.294.0; Thu, 22 Dec 2016 01:40:10 +0000 Date: Thu, 22 Dec 2016 01:40:00 -0000 From: "Maciej W. Rozycki" To: Joseph Myers CC: Aaro Koskinen , , Faraz Shahbazker , "libc-alpha@sourceware.org" , Aurelien Jarno Subject: Re: [RFC] [MIPS] Enable non-executable PT_GNU_STACK support v2 In-Reply-To: Message-ID: References: <56A15768.20005@imgtec.com> <56A157AF.8080504@imgtec.com> <56A6BF93.5010401@imgtec.com> <56B4EC43.7040000@imgtec.com> <20160811210118.GA5342@aurel32.net> <20161222003609.3fdfjx6at2f5ffuv@raspberrypi-2.musicnaut.iki.fi> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-SW-Source: 2016-12/txt/msg00370.txt.bz2 On Thu, 22 Dec 2016, Joseph Myers wrote: > > I thought 4 was reserved for IFUNC, meaning that support for 5 implied > > support for IFUNC (because a simple comparison is all that's available to > > tell whether glibc supports the features required by an executable / > > shared library; it's a single ABI version number, not a bitmask of > > features used) and so the ordering was forced. Certainly the patch here > > lists IFUNC before MIPS_GNU_STACK, and I don't think the libc-abis system > > supports gaps in the numbering (you'd need to put in a dummy name if 4 is > > now to be unused, but then the dummy name would be visible when you run > > libc.so.6, which it shouldn't be). > > The natural way to address that issue, incidentally, would be to reassign > number 4 to MIPS_GNU_STACK and say that IFUNC will get number 5 when > ready. (All the other comments about patch proposals that are explicitly > for review not RFC, with rationale, architecture-independent pieces split > out etc., still apply.) Unfortunately binutils 2.27 have been released which already set ABI version to 5 despite that they do not support IFUNC. So we cannot retroactively make version 5 imply IFUNC support, and consequently we cannot make version 4 imply IFUNC support either, as we work under the assumption that any given ABI version supports all the previous (lower-numbered) ABI versions' features. We can make version 4 imply MIPS_GNU_STACK because it will not break the said assumption, and I suppose it may help with chosing reasonable ABI names for versions 4 and 5 if we cannot support gaps (why?). However IFUNC will have to use version 6 or higher. Have I missed anything? Regrettably I haven't realised I need to veto the binutils change before it was upstreamed, or at least back it out before 2.27 went out; sorry about that. Maciej