From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from albireo.enyo.de (albireo.enyo.de [37.24.231.21]) by sourceware.org (Postfix) with ESMTPS id CD0F0385B835 for ; Thu, 16 Apr 2020 20:18:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org CD0F0385B835 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 1jPAxm-0006kd-Sh; Thu, 16 Apr 2020 20:18:18 +0000 Received: from fw by deneb.enyo.de with local (Exim 4.92) (envelope-from ) id 1jPAxm-0005WN-Nn; Thu, 16 Apr 2020 22:18:18 +0200 From: Florian Weimer To: Nicholas Piggin via Libc-alpha Cc: Rich Felker , Nicholas Piggin , libc-dev@lists.llvm.org, linuxppc-dev@lists.ozlabs.org, musl@lists.openwall.com Subject: Re: [musl] Powerpc Linux 'scv' system call ABI proposal take 2 References: <1586931450.ub4c8cq8dj.astroid@bobo.none> <20200415225539.GL11469@brightrain.aerifal.cx> <1586994952.nnxigedbu2.astroid@bobo.none> <20200416004843.GO11469@brightrain.aerifal.cx> <1587002854.f0slo0111r.astroid@bobo.none> <20200416023542.GP11469@brightrain.aerifal.cx> <1587004907.ioxh0bxsln.astroid@bobo.none> Date: Thu, 16 Apr 2020 22:18:18 +0200 In-Reply-To: <1587004907.ioxh0bxsln.astroid@bobo.none> (Nicholas Piggin via Libc-alpha's message of "Thu, 16 Apr 2020 12:53:31 +1000") Message-ID: <87wo6fchh1.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-8.6 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS, KAM_NUMSUBJECT, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=no 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-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 16 Apr 2020 20:18:23 -0000 * Nicholas Piggin via Libc-alpha: > We may or may not be getting a new ABI that will use instructions not=20 > supported by old processors. > > https://sourceware.org/legacy-ml/binutils/2019-05/msg00331.html > > Current ABI continues to work of course and be the default for some=20 > time, but building for new one would give some opportunity to drop > such support for old procs, at least for glibc. If I recall correctly, during last year's GNU Tools Cauldron, I think it was pretty clear that this was only to be used for intra-DSO ABIs, not cross-DSO optimization. Relocatable object files have an ABI, too, of course, so that's why there's a ABI documentation needed. For cross-DSO optimization, the link editor would look at the DSO being linked in, check if it uses the -mfuture ABI, and apply some shortcuts. But at that point, if the DSO is swapped back to a version built without -mfuture, it no longer works with those newly linked binaries against the -mfuture version. Such a thing is a clear ABI bump, and based what I remember from Cauldron, that is not the plan here. (I don't have any insider knowledge=E2=80=94I just don't want people to read this think: gosh, yet another POWER ABI bump. But the PCREL stuff *is* exciting!)