From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id C79573896829 for ; Tue, 18 May 2021 16:59:19 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org C79573896829 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-517-pVBi9XyCOJikO2NTNTLxOA-1; Tue, 18 May 2021 12:59:17 -0400 X-MC-Unique: pVBi9XyCOJikO2NTNTLxOA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8EC281005D47; Tue, 18 May 2021 16:59:16 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-112-137.ams2.redhat.com [10.36.112.137]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3959119C97; Tue, 18 May 2021 16:59:14 +0000 (UTC) From: Florian Weimer To: Tulio Magno Quites Machado Filho Cc: "Lucas A. M. Magalhaes" , libc-alpha@sourceware.org Subject: Re: [PATCH 2/3] powerpc64le: Check HWCAP bits against compiler build flags References: <162076753769.316372.10532385586864995177@fedora.local> <87im3owe4q.fsf@oldenburg.str.redhat.com> <871racxavs.fsf@linux.ibm.com> Date: Tue, 18 May 2021 18:59:13 +0200 In-Reply-To: <871racxavs.fsf@linux.ibm.com> (Tulio Magno Quites Machado Filho's message of "Wed, 12 May 2021 11:52:23 -0300") Message-ID: <874kf05672.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, 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-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: Tue, 18 May 2021 16:59:21 -0000 * Tulio Magno Quites Machado Filho: > Florian Weimer via Libc-alpha writes: > >> I tried to allude in the commit message that this is expected. Maybe I >> should drop the POWER10 check? > > I don't think this is necessary. > Even if you removed the P10 check, I don't think the P9 check is guaranteed to > work because when _ARCH_PWR9 is set, the compiler is allowed to use P9 > instructions in this function before the test is executed. > > I think this patch is trying to improve the error message to the user. > > With that said, it doesn't hurt to copy your explanation as a source code > comment, i.e.: > > /* This approach does not work for the POWER10 because the bootstrap > relocation already uses PCREL instructions, so the detection code does > not actually run. */ What about this instead? /* This check is not actually reached when building for POWER10 and running on POWER9 because there are faulting PCREL instructions before this point. */ Thanks, Florian