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 639693858036 for ; Sat, 30 Apr 2022 11:27:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 639693858036 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-622-ZExffrq5MiCX2xqPPklM-Q-1; Sat, 30 Apr 2022 07:27:19 -0400 X-MC-Unique: ZExffrq5MiCX2xqPPklM-Q-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3BFBC1C04B7E; Sat, 30 Apr 2022 11:27:19 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.193.187]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 32952815A; Sat, 30 Apr 2022 11:27:18 +0000 (UTC) From: Florian Weimer To: Alan Modra via Libc-alpha Cc: Adhemerval Zanella , Alan Modra Subject: Re: Use __ehdr_start rather than _begin in _dl_start_final References: Date: Sat, 30 Apr 2022 13:27:16 +0200 In-Reply-To: (Alan Modra via Libc-alpha's message of "Sat, 30 Apr 2022 08:31:56 +0930") Message-ID: <87zgk2yfor.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 2.79 on 10.11.54.5 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, SPF_HELO_NONE, SPF_NONE, TXREP 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: Sat, 30 Apr 2022 11:27:22 -0000 * Alan Modra via Libc-alpha: > On Thu, Apr 28, 2022 at 04:37:53PM +0930, Alan Modra wrote: >> On Wed, Apr 27, 2022 at 03:54:27PM -0300, Adhemerval Zanella wrote: >> > >> > >> > On 27/04/2022 09:35, Alan Modra via Libc-alpha wrote: >> > > __ehdr_start is already used in rltld.c:dl_main, and can serve the >> > > same purpose as _begin. Besides tidying the code, using linker >> > > defined section relative symbols rather than "-defsym _begin=0" better >> > > reflects the intent of _dl_start_final use of _begin, which is to >> > > refer to the load address of ld.so rather than absolute address zero. >> > > >> > > The motive for this patch is to finally tidy ppc32 GNU ld treatment of >> > > absolute symbols. On ppc32, the reference to _begin generates a GOT >> > > entry. A GOT entry for an absolute symbol shouldn't be dynamically >> > > relocated, so this usage in glibc of an absolute _begin will fail once >> > > I fix ppc32 ld. Note that on many other targets, including ppc64, gcc >> > > generates pc relative or got-pointer relative addressing for _begin. >> > > ie. the compiler assumes _begin is *not* at an absolute address, and >> > > generally linkers go along with that. >> > >> > Does it mean that once you fix it, newer binutils will start to fail >> > to build older glibc releases for powerpc32? >> >> Not necessarily. I found these issues with absolute symbols in glibc >> by inspecting object files. Possibly dl_rtld_map.l_map_start == 0 >> causes no problem, I'll know when I have set up a test environment for >> ppc32 that lets me build and run a ppc32 glibc. > > Just tst-dl_find_object regresses on a glibc ld.so that uses _begin. I think _dl_find_dso_for_object will go wrong as well, potentially misidentifying dlopen/dlsym/atexit callers. But I think you should proceed with your binutils fix, and we should backport the glibc fix. Thanks, Florian