From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C59A8C433FF for ; Fri, 9 Aug 2019 22:01:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 97E6C2089E for ; Fri, 9 Aug 2019 22:01:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728680AbfHIWBv (ORCPT ); Fri, 9 Aug 2019 18:01:51 -0400 Received: from gate.crashing.org ([63.228.1.57]:43934 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726157AbfHIWBu (ORCPT ); Fri, 9 Aug 2019 18:01:50 -0400 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x79M0hxV029775; Fri, 9 Aug 2019 17:00:43 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x79M0gEs029774; Fri, 9 Aug 2019 17:00:42 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Fri, 9 Aug 2019 17:00:41 -0500 From: Segher Boessenkool To: Christophe Leroy Cc: Arnd Bergmann , clang-built-linux , Linux Kernel Mailing List , linuxppc-dev , Paul Mackerras , Benjamin Herrenschmidt , kbuild test robot , Nathan Chancellor , Michael Ellerman , Nick Desaulniers Subject: Re: [PATCH] powerpc: fix inline asm constraints for dcbz Message-ID: <20190809220041.GO31406@gate.crashing.org> References: <87h873zs88.fsf@concordia.ellerman.id.au> <20190809182106.62130-1-ndesaulniers@google.com> <20190809220301.Horde.AR6y4Bx4WGIq58V9K0En9g4@messagerie.si.c-s.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190809220301.Horde.AR6y4Bx4WGIq58V9K0En9g4@messagerie.si.c-s.fr> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 09, 2019 at 10:03:01PM +0200, Christophe Leroy wrote: > Arnd Bergmann a écrit : > > >On Fri, Aug 9, 2019 at 8:21 PM 'Nick Desaulniers' via Clang Built > >Linux wrote: > > > >> static inline void dcbz(void *addr) > >> { > >>- __asm__ __volatile__ ("dcbz %y0" : : "Z"(*(u8 *)addr) : "memory"); > >>+ __asm__ __volatile__ ("dcbz %y0" : "=Z"(*(u8 *)addr) :: "memory"); > >> } > >> > >> static inline void dcbi(void *addr) > >> { > >>- __asm__ __volatile__ ("dcbi %y0" : : "Z"(*(u8 *)addr) : "memory"); > >>+ __asm__ __volatile__ ("dcbi %y0" : "=Z"(*(u8 *)addr) :: "memory"); > >> } > > > >I think the result of the discussion was that an output argument only > >kind-of > >makes sense for dcbz, but for the others it's really an input, and clang is > >wrong in the way it handles the "Z" constraint by making a copy, which it > >doesn't do for "m". > > > >I'm not sure whether it's correct to use "m" instead of "Z" here, which > >would be a better workaround if that works. More importantly though, > >clang really needs to be fixed to handle "Z" correctly. > > As the benefit is null, I think the best is probably to reverse my > original commit until at least CLang is fixed, as initialy suggested > by mpe And what about the other uses of "Z"? Also, if you use C routines (instead of assembler code) for the basic "clear a block" and the like routines, as there have been patches for recently, the benefit is not zero. Segher