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 0F7EFC31E4B for ; Fri, 14 Jun 2019 13:09:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D84B620850 for ; Fri, 14 Jun 2019 13:09:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727928AbfFNNJq (ORCPT ); Fri, 14 Jun 2019 09:09:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49814 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726874AbfFNNJp (ORCPT ); Fri, 14 Jun 2019 09:09:45 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 5F695368E0; Fri, 14 Jun 2019 13:09:35 +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 19C891001B1B; Fri, 14 Jun 2019 13:09:28 +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> <914051741.43025.1560348011775.JavaMail.zimbra@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> Date: Fri, 14 Jun 2019 15:09:27 +0200 In-Reply-To: <1085273942.3137.1560517301721.JavaMail.zimbra@efficios.com> (Mathieu Desnoyers's message of "Fri, 14 Jun 2019 09:01:41 -0400 (EDT)") Message-ID: <87d0jguxdk.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 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Fri, 14 Jun 2019 13:09:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * 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. Thanks, Florian