From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 6A19A385AC3F for ; Thu, 13 Jan 2022 17:32:27 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 6A19A385AC3F Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-664-c5ArLhnkNcqo84iaSwdrug-1; Thu, 13 Jan 2022 12:32:25 -0500 X-MC-Unique: c5ArLhnkNcqo84iaSwdrug-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 815BB1923B80; Thu, 13 Jan 2022 17:32:24 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.49]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7723B106C065; Thu, 13 Jan 2022 17:32:23 +0000 (UTC) From: Florian Weimer To: Andreas Schwab Cc: libc-alpha@sourceware.org Subject: Re: [PATCH] Fix glibc 2.34 ABI omission (missing GLIBC_2.34 in dynamic loader) References: <87h7bjmnt0.fsf@oldenburg.str.redhat.com> <87czm7qv2f.fsf@igel.home> <875yrzmmw6.fsf@oldenburg.str.redhat.com> <878rwvqtyc.fsf@igel.home> <87sfv3l7ag.fsf@oldenburg.str.redhat.com> <87y2497rp5.fsf@oldenburg.str.redhat.com> Date: Thu, 13 Jan 2022 18:32:21 +0100 In-Reply-To: <87y2497rp5.fsf@oldenburg.str.redhat.com> (Florian Weimer via Libc-alpha's message of "Fri, 24 Dec 2021 20:01:26 +0100") Message-ID: <87zgnzy21m.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-5.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, URIBL_BLACK autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 13 Jan 2022 17:32:28 -0000 * Florian Weimer via Libc-alpha: > * Florian Weimer via Libc-alpha: > >> * Andreas Schwab: >> >>> On Dez 08 2021, Florian Weimer wrote: >>> >>>> * Andreas Schwab: >>>> >>>>> On Dez 08 2021, Florian Weimer via Libc-alpha wrote: >>>>> >>>>>> The glibc 2.34 release really should have added a GLIBC_2.34 >>>>>> symbol to the dynamic loader. >>>>> >>>>> Well, the ship has sailed. >>>> >>>> Has it? It's just software, we can change it. >>> >>> ABI is not software, it's a contract. >> >> But sometimes we have to to fix bugs. Again, what I propose is quite >> different from a simple symbol change because distributions and users >> can fix this now, well before the symbol is going to be used. >> >> I have considered using a stub DSO and mention that instead of libc.so.6 >> in the libc.so linker script. But I'm not sure how we can prevent users >> from linking against the moved symbol by bypassing the linker script. >> That would produce ABI-incompatible binaries. We could turn it into a >> compat symbol, but as long as it's in the dynamic symbol table, some >> people will use it. > > Let me propose a look at this from a different angle. > > Let's say we do not apply this change. Then if we move dlopen (say) > into ld.so, it needs to have a new symbol version, say dlopen@GLIBC_2.36 > (to enable early errors on old glibc even with lazy binding). The net > result will be that dlopen-using binaries linked against glibc 2.36 or > later will not work with glibc 2.34. > > Binaries linked against glibc 2.34 with or without the proposed change > are fully interoperable (forwards and backwards compatible). No new > symbol version/soname combination is ever generated by the link editor > because the GLIBC_2.34 version in ld.so is effectively empty. > Considering the moved dlopen, we would give it version of > dlopen@GLIBC_2.34 (even if the symbol is added in glibc 2.36). Binaries > linked against glibc 2.36 will still fail when running at the initial > version of glibc 2.34. But with the proposed patch here, they will work > even with glibc 2.34. This means that there are no ABI > incompatibilities introduce by this patch, and we enable compatibility > with future symbol moves. Andreas, do you find this line of reasoning convincing? Thanks, Florian