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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 74A90C5AC75 for ; Tue, 25 Jan 2022 23:39:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234929AbiAYXjf (ORCPT ); Tue, 25 Jan 2022 18:39:35 -0500 Received: from gate.crashing.org ([63.228.1.57]:54754 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234898AbiAYXjb (ORCPT ); Tue, 25 Jan 2022 18:39:31 -0500 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 20PNVUiB032739; Tue, 25 Jan 2022 17:31:30 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 20PNVSKH032738; Tue, 25 Jan 2022 17:31:28 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Tue, 25 Jan 2022 17:31:28 -0600 From: Segher Boessenkool To: Nick Desaulniers Cc: Josh Poimboeuf , Borislav Petkov , Vasily Gorbik , Linus Torvalds , Ingo Molnar , Dave Hansen , Thomas Gleixner , Peter Zijlstra , Luc Van Oostenryck , x86@kernel.org, llvm@lists.linux.dev, linux-sparse@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot , Nathan Chancellor , linux-toolchains@vger.kernel.org Subject: Re: [PATCH] objtool: prefer memory clobber & %= to volatile & __COUNTER__ Message-ID: <20220125233128.GT614@gate.crashing.org> References: <20220114010526.1776605-1-ndesaulniers@google.com> <20220118192256.jzk5dnceeusq7x7u@treble> <20220118230120.pivvson7qekfiqic@treble> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! On Mon, Jan 24, 2022 at 03:26:36PM -0800, Nick Desaulniers wrote: > I noticed in that report and > https://lore.kernel.org/lkml/202201190702.XNSXrMTK-lkp@intel.com/ > that gcc-9 was used. I wonder if %= has been fixed in gcc-10+? Have > there been other reports with gcc-10+ for my patch? None of the %= code (which is trivial) has been changed since 1992. > If this is fixed in gcc-10, then we can probably add a comment with a > FIXME link to the issue or commit to replace __COUNTER__ with %= one > day. If not, then we can probably come up with a reduced test case > for the GCC devs to take a look at, then add the FIXME comment to > kernel sources. Please open a PR? > I'm more confident that we can remove the `volatile` keyword (I was > thinking about adding a new diagnostic to clang to warn that volatile > is redundate+implied for asm goto or inline asm that doesn't have > outputs) though that's not the problem here and will probably generate > some kernel wide cleanup before we could enable such a flag. Its main value is that it would discourage users from thinking volatile is magic. Seriously worth some pain! > Perhaps > there are known compiler versions that still require the keyword for > those cases for some reason. It was removed from compiler-gcc.h in 3347acc6fcd4 (which changed the minimum required GCC version to GCC 5). Segher