From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 121208 invoked by alias); 21 Sep 2017 11:19:57 -0000 Mailing-List: contact gdb-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sourceware.org Received: (qmail 121186 invoked by uid 89); 21 Sep 2017 11:19:55 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD,SPF_PASS autolearn=ham version=3.3.2 spammy=HContent-Transfer-Encoding:8bit X-Spam-User: qpsmtpd, 2 recipients X-HELO: foss.arm.com Received: from foss.arm.com (HELO foss.arm.com) (217.140.101.70) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 21 Sep 2017 11:19:54 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 13B4880D; Thu, 21 Sep 2017 04:19:53 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 86C3F3F58C; Thu, 21 Sep 2017 04:19:50 -0700 (PDT) Date: Thu, 21 Sep 2017 11:19:00 -0000 From: Dave Martin To: Alan Hayward Cc: Dave Martin , "linux-arch@vger.kernel.org" , "libc-alpha@sourceware.org" , "gdb@sourceware.org" , Ard Biesheuvel , Szabolcs Nagy , Catalin Marinas , Yao Qi , Will Deacon , Richard Sandiford , nd , Alex =?iso-8859-1?Q?Benn=E9e?= , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v2 14/28] arm64/sve: Backend logic for setting the vector length Message-ID: <20170921111937.GA17434@e103592.cambridge.arm.com> References: <1504198860-12951-1-git-send-email-Dave.Martin@arm.com> <1504198860-12951-15-git-send-email-Dave.Martin@arm.com> <20170920110902.GG24231@e103592.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-SW-Source: 2017-09/txt/msg00073.txt.bz2 On Wed, Sep 20, 2017 at 06:08:21PM +0000, Alan Hayward wrote: > > > On 20 Sep 2017, at 12:09, Dave Martin wrote: [...] > >> Given, sve_set_vector_length is called when setting the vector length in > >> PTRACE_SETREGSET, it looks to me like if you set VL to a value that’s not > >> supported by the hardware, then it’s going to round down to the previous value. > >> Is that correct? I’m not sure if that’s explained in the docs? > > > > Does this cover it? > > > > "On success, the calling thread's vector length is changed to the > > largest value supported by the system that is less than or equal to vl." > > > > (For ptrace, I just cross-reference the PR_SVE_SET_VL behaviour, above.) > > For ptrace is it worth mentioning user should do a GET after a SET to confirm > what VL value was actually set? This seems worth a clarification -- I'd thought this was already mentioned, but it isn't. How about: The caller must make a further GETREGSET call if it needs to know what VL is actually set by SETREGSET, unless is it known in advance that the requested VL is supported. [...] Cheers ---Dave