From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <fw@deneb.enyo.de>
Received: from albireo.enyo.de (albireo.enyo.de [37.24.231.21])
 by sourceware.org (Postfix) with ESMTPS id 7F2C4389851E
 for <libc-help@sourceware.org>; Thu, 17 Dec 2020 20:55:17 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 7F2C4389851E
Authentication-Results: sourceware.org;
 dmarc=none (p=none dis=none) header.from=deneb.enyo.de
Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=fw@deneb.enyo.de
Received: from [172.17.203.2] (helo=deneb.enyo.de)
 by albireo.enyo.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256)
 id 1kq0It-0000db-WD; Thu, 17 Dec 2020 20:55:16 +0000
Received: from fw by deneb.enyo.de with local (Exim 4.92)
 (envelope-from <fw@deneb.enyo.de>)
 id 1kq0It-0005EB-Rf; Thu, 17 Dec 2020 21:55:15 +0100
From: Florian Weimer <fw@deneb.enyo.de>
To: Ryan Burn <rnickb731@gmail.com>
Cc: Ryan Burn via Libc-help <libc-help@sourceware.org>
Subject: Re: Trouble with portable linking
References: <CACqP_wyc_RU8uMsRaPgrER-yWb4DqdT=wT35wOG6H6pmpWL9BQ@mail.gmail.com>
 <87lfdwdwb4.fsf@mid.deneb.enyo.de>
 <CACqP_wwR2zeXZgtwASAXQ7+HFXz85DeLA8zZH2RGJKGwkiC8vA@mail.gmail.com>
Date: Thu, 17 Dec 2020 21:55:15 +0100
In-Reply-To: <CACqP_wwR2zeXZgtwASAXQ7+HFXz85DeLA8zZH2RGJKGwkiC8vA@mail.gmail.com>
 (Ryan Burn's message of "Thu, 17 Dec 2020 12:47:44 -0800")
Message-ID: <87zh2ccfv0.fsf@mid.deneb.enyo.de>
MIME-Version: 1.0
Content-Type: text/plain
X-Spam-Status: No, score=-6.1 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS,
 SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on
 server2.sourceware.org
X-BeenThere: libc-help@sourceware.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Libc-help mailing list <libc-help.sourceware.org>
List-Unsubscribe: <https://sourceware.org/mailman/options/libc-help>,
 <mailto:libc-help-request@sourceware.org?subject=unsubscribe>
List-Archive: <https://sourceware.org/pipermail/libc-help/>
List-Help: <mailto:libc-help-request@sourceware.org?subject=help>
List-Subscribe: <https://sourceware.org/mailman/listinfo/libc-help>,
 <mailto:libc-help-request@sourceware.org?subject=subscribe>
X-List-Received-Date: Thu, 17 Dec 2020 20:55:19 -0000

* Ryan Burn:

> On Thu, Dec 17, 2020 at 12:14 PM Florian Weimer <fw@deneb.enyo.de> wrote:
>
>> If you want to be compatible with glibc versions that check the
>> embedded soname in symbol versions (which is not visible in the @
>> syntax), you need to build a stub library that defines the required
>> symbol versions in the right shared object.  There is no way to
>> achieve this with .symver directives.
>
> Thanks for the response! Could you elaborate a little more on how I
> can build the stub library?

Here's a script that generates such a stub DSO from an existing full
DSO:

<https://git.centos.org/rpms/compat-glibc/blob/c7/f/SOURCES/dummylib.sh>

It is not completely correct for data symbols; that part needs a bit
of tweaking to get the alignment right.  The resulting assembler file
is architecture-specific because the object sizes and symbol versions
are.

> If I understand correctly, newer versions of glibc will resolve a
> versioned symbol even if the embedded soname doesn't match. Is there a
> way to explicitly define the soname so that I can specify it to
> libpthread?

The link editor copies the soname of the shared object that contains a
versioned symbol definition when it generates the versioned symbol
reference.  That's why I think you need that stub DSO.  It's the only
way I know of that actually works.