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,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 97E06C76191 for ; Sun, 21 Jul 2019 18:02:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E11720828 for ; Sun, 21 Jul 2019 18:02:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727197AbfGUSCW (ORCPT ); Sun, 21 Jul 2019 14:02:22 -0400 Received: from gate.crashing.org ([63.228.1.57]:40017 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726902AbfGUSCV (ORCPT ); Sun, 21 Jul 2019 14:02:21 -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 x6LI1qEv002640; Sun, 21 Jul 2019 13:01:52 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x6LI1oKj002637; Sun, 21 Jul 2019 13:01:50 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Sun, 21 Jul 2019 13:01:50 -0500 From: Segher Boessenkool To: Nathan Chancellor Cc: Christophe Leroy , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH v2] powerpc: slightly improve cache helpers Message-ID: <20190721180150.GN20882@gate.crashing.org> References: <45hnfp6SlLz9sP0@ozlabs.org> <20190708191416.GA21442@archlinux-threadripper> <20190709064952.GA40851@archlinux-threadripper> <20190719032456.GA14108@archlinux-threadripper> <20190719152303.GA20882@gate.crashing.org> <20190719160455.GA12420@archlinux-threadripper> <20190721075846.GA97701@archlinux-threadripper> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190721075846.GA97701@archlinux-threadripper> 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 Sun, Jul 21, 2019 at 12:58:46AM -0700, Nathan Chancellor wrote: > I have attached the disassembly of arch/powerpc/kernel/mem.o with > clear_page (working) and broken_clear_page (broken), along with the side > by side diff. My assembly knowledge is fairly limited as it stands and > it is certainly not up to snuff on PowerPC so I have no idea what I am > looking for. Please let me know if anything immediately looks off or if > there is anything else I can do to help out. You might want to use a disassembler that shows most simplified mnemonics, and you crucially should show the relocations. "objdump -dr" works nicely. > 0000017c clear_user_page: > 17c: 38 80 00 80 li 4, 128 > 180: 7c 89 03 a6 mtctr 4 > 184: 7c 00 1f ec dcbz 0, 3 > 188: 38 63 00 20 addi 3, 3, 32 > 18c: 42 00 ff f8 bdnz .+65528 That offset is incorrectly disassembled, btw (it's a signed field, not unsigned). > 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. Segher