From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.0 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 152CB1F462 for ; Fri, 14 Jun 2019 13:24:58 +0000 (UTC) DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:cc:subject:references:date:in-reply-to :message-id:mime-version:content-type; q=dns; s=default; b=RCBO7 JqWfSCMqxb76o6FDLO3JpGkeR7WrQAo93Eg5hAYDnSfefpo2moK5zTB0g+EwxuaW MGsTNOTyhh1AY/BCqFSfOVjx/H/ErA5icangErjhTkrHeAiMXuNOXwraqdTVALnp I14s4XuM5k3u2a1IYKaNh4oTvFnkj1UbcPOSP8= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:cc:subject:references:date:in-reply-to :message-id:mime-version:content-type; s=default; bh=McZwyHnxQhn sDCa8XnyMVYmvwRI=; b=BnJOiVhMGNDAgBLssySMMfV5t5IZfu/1rHewupIgOA3 mqzDQycoRc5UXzkLAesngaZ1wq9YMypWqYglZBqrWy64PUT1jsH2JoxrO89uD8GI 1AYOhMklwiHjQrsBbewA/mxnRT+2Q9zzTSgRO8dZLdcn8uXL5IpG8wVB8PeOjsfQ = Received: (qmail 88083 invoked by alias); 14 Jun 2019 13:24:45 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 87958 invoked by uid 89); 14 Jun 2019 13:24:40 -0000 Authentication-Results: sourceware.org; auth=none X-HELO: mx1.redhat.com 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 * 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