From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by sourceware.org (Postfix) with ESMTP id 3E5513814FC9 for ; Tue, 24 May 2022 17:40:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 3E5513814FC9 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=kernel.crashing.org Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 24OHcFD0025599; Tue, 24 May 2022 12:38:15 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 24OHcEu5025598; Tue, 24 May 2022 12:38:14 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Tue, 24 May 2022 12:38:14 -0500 From: Segher Boessenkool To: Nicholas Piggin Cc: linuxppc-dev@lists.ozlabs.org, libc-alpha@sourceware.org, gcc@gcc.gnu.org, Paul E Murphy , Peter Bergner , Michael Ellerman Subject: Re: [PATCH Linux] powerpc: add documentation for HWCAPs Message-ID: <20220524173814.GH25951@gate.crashing.org> References: <20220524093828.505575-1-npiggin@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220524093828.505575-1-npiggin@gmail.com> User-Agent: Mutt/1.4.2.3i X-Spam-Status: No, score=-3.2 required=5.0 tests=BAYES_00, JMQ_SPF_NEUTRAL, KAM_DMARC_STATUS, SPF_HELO_PASS, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 24 May 2022 17:40:21 -0000 Hi! On Tue, May 24, 2022 at 07:38:28PM +1000, Nicholas Piggin wrote: > Thanks for all the comments and corrections. It should be nearing the > point where it is useful now. Yes I do think it would be useful to align > this more with OpenPOWER docs (and possibly eventually move it into the > ABI, given that's the allocator of these numbers) but that's not > done yet. The auxiliary vector is a Linux/glibc thing, it should not be described in more generic ABI documents. It is fine where you have it now afaics. > +Where software relies on a feature described by a HWCAP, it should check the > +relevant HWCAP flag to verify that the feature is present before attempting to > +make use of the feature. > + > +Features should not be probed through other means. When a feature is not > +available, attempting to use it may result in unpredictable behaviour, and > +may not be guaranteed to result in any reliable indication that the feature > +is unavailable. Traditionally VMX was tested for by simply executing an instruction and catching SIGILL. This is portable even. This has worked fine for over two decades, it's a bit weird to declare this a forbidden practice now :-) It certainly isn't recommended for more complex and/or newer things. > +verstions. (typo. spellcheck maybe?) Segher