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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 38241C432BE for ; Thu, 26 Aug 2021 13:54:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0A95E60EFF for ; Thu, 26 Aug 2021 13:54:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242731AbhHZNzW (ORCPT ); Thu, 26 Aug 2021 09:55:22 -0400 Received: from gate.crashing.org ([63.228.1.57]:35066 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229793AbhHZNzU (ORCPT ); Thu, 26 Aug 2021 09:55:20 -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 17QDlx1Q018576; Thu, 26 Aug 2021 08:47:59 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 17QDlwDa018574; Thu, 26 Aug 2021 08:47:58 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Thu, 26 Aug 2021 08:47:58 -0500 From: Segher Boessenkool To: Christophe Leroy Cc: Michael Ellerman , Nathan Chancellor , llvm@lists.linux.dev, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, Paul Mackerras , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v2 2/2] powerpc/bug: Provide better flexibility to WARN_ON/__WARN_FLAGS() with asm goto Message-ID: <20210826134758.GZ1583@gate.crashing.org> References: <389962b1b702e3c78d169e59bcfac56282889173.1618331882.git.christophe.leroy@csgroup.eu> <87h7fcc2m4.fsf@mpe.ellerman.id.au> <3fad8702-278a-d9f9-1882-6958ce570bcc@csgroup.eu> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3fad8702-278a-d9f9-1882-6958ce570bcc@csgroup.eu> User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 26, 2021 at 08:37:09AM +0200, Christophe Leroy wrote: > Le 26/08/2021 à 05:21, Michael Ellerman a écrit : > >This patch seems to fix it. Not sure if that's just papering over it > >though. > > > >diff --git a/arch/powerpc/include/asm/bug.h > >b/arch/powerpc/include/asm/bug.h > >index 1ee0f22313ee..75fcb4370d96 100644 > >--- a/arch/powerpc/include/asm/bug.h > >+++ b/arch/powerpc/include/asm/bug.h > >@@ -119,7 +119,7 @@ __label_warn_on: \ > > \ > > WARN_ENTRY(PPC_TLNEI " %4, 0", \ > > BUGFLAG_WARNING | > > BUGFLAG_TAINT(TAINT_WARN), \ > >- __label_warn_on, "r" (x)); \ > >+ __label_warn_on, "r" (!!(x))); \ > > break; \ > > __label_warn_on: \ > > __ret_warn_on = true; \ > > But for a simple WARN_ON() call: > > void test(unsigned long b) > { > WARN_ON(b); > } > > Without your change with GCC you get: > > 00000000000012d0 <.test>: > 12d0: 0b 03 00 00 tdnei r3,0 > 12d4: 4e 80 00 20 blr > > > With the !! change you get: > > 00000000000012d0 <.test>: > 12d0: 31 23 ff ff addic r9,r3,-1 > 12d4: 7d 29 19 10 subfe r9,r9,r3 > 12d8: 0b 09 00 00 tdnei r9,0 > 12dc: 4e 80 00 20 blr That is because the asm (unlike the builtin) cannot be optimised by the compiler. Segher