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 77489C76190 for ; Mon, 22 Jul 2019 18:01:00 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0E736218BE for ; Mon, 22 Jul 2019 18:01:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E736218BE Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45sqCt1ZyCzDqDm for ; Tue, 23 Jul 2019 04:00:58 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=permerror (mailfrom) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 45sq9966mxzDqKj for ; Tue, 23 Jul 2019 03:58:37 +1000 (AEST) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x6MHwIwq002804; Mon, 22 Jul 2019 12:58:18 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x6MHwH9G002785; Mon, 22 Jul 2019 12:58:17 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Mon, 22 Jul 2019 12:58:17 -0500 From: Segher Boessenkool To: Nick Desaulniers Subject: Re: [PATCH v2] powerpc: slightly improve cache helpers Message-ID: <20190722175817.GE20882@gate.crashing.org> References: <20190709064952.GA40851@archlinux-threadripper> <20190719032456.GA14108@archlinux-threadripper> <20190719152303.GA20882@gate.crashing.org> <20190719160455.GA12420@archlinux-threadripper> <20190721075846.GA97701@archlinux-threadripper> <20190721180150.GN20882@gate.crashing.org> <20190722024140.GA55142@archlinux-threadripper> <20190722061940.GZ20882@gate.crashing.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: LKML , clang-built-linux , Paul Mackerras , Nathan Chancellor , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Jul 22, 2019 at 10:21:07AM -0700, Nick Desaulniers wrote: > On Sun, Jul 21, 2019 at 11:19 PM Segher Boessenkool > wrote: > > On Sun, Jul 21, 2019 at 07:41:40PM -0700, Nathan Chancellor wrote: > > > On Sun, Jul 21, 2019 at 01:01:50PM -0500, Segher Boessenkool wrote: > > > > On Sun, Jul 21, 2019 at 12:58:46AM -0700, Nathan Chancellor wrote: > > > > > 0000017c clear_user_page: > > > > > 17c: 94 21 ff f0 stwu 1, -16(1) > > > > > 180: 38 80 00 80 li 4, 128 > > > > > 184: 38 63 ff e0 addi 3, 3, -32 > > > > > 188: 7c 89 03 a6 mtctr 4 > > > > > 18c: 38 81 00 0f addi 4, 1, 15 > > > > > 190: 8c c3 00 20 lbzu 6, 32(3) > > > > > 194: 98 c1 00 0f stb 6, 15(1) > > > > > 198: 7c 00 27 ec dcbz 0, 4 > > > > > 19c: 42 00 ff f4 bdnz .+65524 > > > > > > > > Uh, yeah, well, I have no idea what clang tried here, but that won't > > > > work. It's copying a byte from each target cache line to the stack, > > > > and then does clears the cache line containing that byte on the stack. > > > > > > > > I *guess* this is about "Z" and not about "%y", but you'll have to ask > > > > the clang people. > > > > > > > > Or it may be that they do not treat inline asm operands as lvalues > > > > properly? That rings some bells. Yeah that looks like it. > > > > The code is > > __asm__ __volatile__ ("dcbz %y0" : : "Z"(*(u8 *)addr) : "memory"); > > > > so yeah it looks like clang took that *(u8 *)addr as rvalue, and > > stored that in stack, and then used *that* as memory. > > What's the %y modifier supposed to mean here? It prints a memory address for an indexed operand. If you write just "%0" it prints addresses that are a single register as "0(r3)" instead of "0,r3". Some instructions do not allow offset form. > addr is in the list of > inputs, so what's wrong with using it as an rvalue? It seems to use *(u8 *)addr as rvalue. Asm operands are lvalues. It matters a lot for memory operands. > > Maybe clang simply does not not to treat "Z" the same as "m"? (And "Y" > > and "Q" and "es" and a whole bunch of "w*", what about those?) Segher