From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B1019C31E4B for ; Fri, 14 Jun 2019 13:24:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F1762133D for ; Fri, 14 Jun 2019 13:24:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728094AbfFNNYi (ORCPT ); Fri, 14 Jun 2019 09:24:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40634 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727729AbfFNNYh (ORCPT ); Fri, 14 Jun 2019 09:24:37 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E82FD31628E1; Fri, 14 Jun 2019 13:24:31 +0000 (UTC) Received: from oldenburg2.str.redhat.com (dhcp-192-180.str.redhat.com [10.33.192.180]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 918A339C3; Fri, 14 Jun 2019 13:24:25 +0000 (UTC) From: Florian Weimer To: Mathieu Desnoyers Cc: carlos , Joseph Myers , Szabolcs Nagy , libc-alpha , Thomas Gleixner , Ben Maurer , Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , Will Deacon , Dave Watson , Paul Turner , Rich Felker , linux-kernel , linux-api Subject: Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10) References: <20190503184219.19266-1-mathieu.desnoyers@efficios.com> <802638054.3032.1560506584705.JavaMail.zimbra@efficios.com> <87ftocwkei.fsf@oldenburg2.str.redhat.com> <1635690189.3049.1560507249693.JavaMail.zimbra@efficios.com> <87tvcsv1pk.fsf@oldenburg2.str.redhat.com> <1190407525.3131.1560516910936.JavaMail.zimbra@efficios.com> <1085273942.3137.1560517301721.JavaMail.zimbra@efficios.com> <87d0jguxdk.fsf@oldenburg2.str.redhat.com> <1779359826.3226.1560518318701.JavaMail.zimbra@efficios.com> Date: Fri, 14 Jun 2019 15:24:24 +0200 In-Reply-To: <1779359826.3226.1560518318701.JavaMail.zimbra@efficios.com> (Mathieu Desnoyers's message of "Fri, 14 Jun 2019 09:18:38 -0400 (EDT)") Message-ID: <87wohoti47.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Fri, 14 Jun 2019 13:24:37 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mathieu Desnoyers: > ----- On Jun 14, 2019, at 3:09 PM, Florian Weimer fweimer@redhat.com wrote: > >> * Mathieu Desnoyers: >> >>> But my original issue remains: if I define a variable called __rseq_handled >>> within either the main executable or the preloaded library, it overshadows >>> the libc one: >>> >>> efficios@compudjdev:~/test/libc-sym$ ./a >>> __rseq_handled main: 0 0x56135fd5102c >>> __rseq_abi.cpu_id main: 29 0x7fcbeca6d5a0 >>> efficios@compudjdev:~/test/libc-sym$ LD_PRELOAD=./s.so ./a >>> __rseq_handled s.so: 0 0x558f70aeb02c >>> __rseq_abi.cpu_id s.so: -1 0x7fdca78b7760 >>> __rseq_handled main: 0 0x558f70aeb02c >>> __rseq_abi.cpu_id main: 27 0x7fdca78b7760 >>> >>> Which is unexpected. >> >> Why is this unexpected? It has to be this way if the main program uses >> a copy relocation of __rseq_handled. As long as there is just one >> address across the entire program and ld.so initializes the copy of the >> variable that is actually used, everything will be fine. > > Here is a printout of the __rseq_handled address observed by ld.so, it > does not match: > > LD_PRELOAD=./s.so ./a > elf: __rseq_handled addr: 7f501c98a140 > __rseq_handled s.so: 0 0x55817a88d02c > __rseq_abi.cpu_id s.so: -1 0x7f501c983760 > __rseq_handled main: 0 0x55817a88d02c > __rseq_abi.cpu_id main: 27 0x7f501c983760 Where do you print the address? Before or after the self-relocation of the dynamic loader? The address is only correct after self-relocation. Thanks, Florian