From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <libc-alpha-return-102711-listarch-libc-alpha=sources.redhat.com@sourceware.org>
Received: (qmail 59422 invoked by alias); 14 Jun 2019 13:09:47 -0000
Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm
Precedence: bulk
List-Id: <libc-alpha.sourceware.org>
List-Subscribe: <mailto:libc-alpha-subscribe@sourceware.org>
List-Archive: <http://sourceware.org/ml/libc-alpha/>
List-Post: <mailto:libc-alpha@sourceware.org>
List-Help: <mailto:libc-alpha-help@sourceware.org>, <http://sourceware.org/ml/#faqs>
Sender: libc-alpha-owner@sourceware.org
Received: (qmail 59412 invoked by uid 89); 14 Jun 2019 13:09:47 -0000
Authentication-Results: sourceware.org; auth=none
X-Spam-SWARE-Status: No, score=-6.5 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS autolearn=ham version=3.3.1 spammy=H*f:sk:1085273, H*i:sk:1085273
X-HELO: mx1.redhat.com
From: Florian Weimer <fweimer@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: carlos <carlos@redhat.com>,  Joseph Myers <joseph@codesourcery.com>,  Szabolcs Nagy <szabolcs.nagy@arm.com>,  libc-alpha <libc-alpha@sourceware.org>,  Thomas Gleixner <tglx@linutronix.de>,  Ben Maurer <bmaurer@fb.com>,  Peter Zijlstra <peterz@infradead.org>,  "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,  Boqun Feng <boqun.feng@gmail.com>,  Will Deacon <will.deacon@arm.com>,  Dave Watson <davejwatson@fb.com>,  Paul Turner <pjt@google.com>,  Rich Felker <dalias@libc.org>,  linux-kernel <linux-kernel@vger.kernel.org>,  linux-api <linux-api@vger.kernel.org>
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>
	<c16c9785-7f8c-430b-a4df-a53e47bf1600@redhat.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 13:09:00 -0000
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-SW-Source: 2019-06/txt/msg00320.txt.bz2

* 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