From owner-freebsd-hackers@freebsd.org Fri Feb 21 12:03:30 2020 Return-Path: Delivered-To: freebsd-hackers@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 6195025BB91 for ; Fri, 21 Feb 2020 12:03:30 +0000 (UTC) (envelope-from joerg@bec.de) Received: from relay8-d.mail.gandi.net (relay8-d.mail.gandi.net [217.70.183.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 48P98d3tKFz45jn for ; Fri, 21 Feb 2020 12:03:29 +0000 (UTC) (envelope-from joerg@bec.de) X-Originating-IP: 93.205.161.59 Received: from bec.de (p5DCDA13B.dip0.t-ipconnect.de [93.205.161.59]) (Authenticated sender: joerg@bec.de) by relay8-d.mail.gandi.net (Postfix) with ESMTPSA id 9BC611BF209 for ; Fri, 21 Feb 2020 12:03:27 +0000 (UTC) Date: Fri, 21 Feb 2020 13:03:25 +0100 From: Joerg Sonnenberger To: freebsd-hackers@freebsd.org Subject: Re: How much libc++ ABI changes FreeBSD can consume? Message-ID: <20200221120325.GA86511@bec.de> Mail-Followup-To: freebsd-hackers@freebsd.org References: <20200220141655.GP29554@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.3 (2019-02-01) X-Rspamd-Queue-Id: 48P98d3tKFz45jn X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=none (mx1.freebsd.org: domain of joerg@bec.de has no SPF policy when checking 217.70.183.201) smtp.mailfrom=joerg@bec.de X-Spamd-Result: default: False [-1.33 / 15.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; HAS_XOIP(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; IP_SCORE(-1.26)[ip: (-3.45), ipnet: 217.70.176.0/20(-1.57), asn: 29169(-1.27), country: FR(0.00)]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-hackers@freebsd.org]; TO_DN_NONE(0.00)[]; AUTH_NA(1.00)[]; RCPT_COUNT_ONE(0.00)[1]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; RECEIVED_SPAMHAUS_PBL(0.00)[59.161.205.93.khpj7ygk5idzvmvt5x4ziurxhy.zen.dq.spamhaus.net : 127.0.0.10]; MIME_TRACE(0.00)[0:+]; DMARC_NA(0.00)[bec.de]; NEURAL_HAM_MEDIUM(-0.87)[-0.865,0]; R_SPF_NA(0.00)[]; RCVD_IN_DNSWL_LOW(-0.10)[201.183.70.217.list.dnswl.org : 127.0.5.1]; R_DKIM_NA(0.00)[]; SUBJECT_ENDS_QUESTION(1.00)[]; ASN(0.00)[asn:29169, ipnet:217.70.176.0/20, country:FR]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 21 Feb 2020 12:03:30 -0000 On Fri, Feb 21, 2020 at 03:24:32AM -0600, Zhihao Yuan wrote: > On Thu, Feb 20, 2020 at 8:17 AM Konstantin Belousov wrote: > > > > 3. Is MFC required for libc++ updates? If so, how > > > does that affect ABI changes? > > It is highly desirable to get libc++ synced between head and all actively > > supported stable versions. > > > > > 4. Is there any desire to make C++ ABI breakage > > > smoother by ultilzing mechanisms such as > > > Symbol.map? > > Yes. More expanded answer below. > > > > Right now any libc++ ABI breakage requires dso version bump. We try hard > > to avoid that because it trivially leads to a situation when multiple > > libc++'s are loaded into same process, unless everything is recompiled > > against same lib. In other words, bumping version for such fundamental > > library is too troublesome. > > > > Symver provides a solution for gradual ABI changes, but by policy > > we never provide symbol versioning for third-party libraries unless > > upstream maintains the versioning. The reason is that we cannot enforce > > upstream ABI policy, which would make versioning broken by updates and > > then pointless. > > > > So for instance libstdc++.so from gcc is versioned, while ncurses are not. > > > > To summarize what I heard, even if libc++ > stabilizes V2 ABI, we do not want to do an > "ABI break since release 1X" thing. If we > really upgrade, we break all stable versions. > And we hope/encourage libc++ to > version symbols like what libstdc++ does, > correct? Symbol versioning helps really little for this kind of ABI breaks. It still ends up effectively being a flag day as libraries build before and after don't interact that well with each other. Joerg