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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 2AC70C433ED for ; Wed, 19 May 2021 06:57:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F42116135B for ; Wed, 19 May 2021 06:57:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238396AbhESG6x (ORCPT ); Wed, 19 May 2021 02:58:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233136AbhESG6s (ORCPT ); Wed, 19 May 2021 02:58:48 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A137C06175F; Tue, 18 May 2021 23:57:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=yR4HIbsOuCNiqwnMZ6oojYJI0qVF+NxXEr3UMzE7jxc=; b=sEYpWJdC/PkF58DyVztc24qcVs PHCyER2RbURnpPPvO7FOu8JWqaQy7X55rAuUUhdF6Xb9nUaIC2O2bW8TjC70kU/JyQnHYkbrqzQPa vEAib/TCCJXUY530heLmmpXuYXBt2uGdYCkEv8jyWm1qXDmme9Qwpn8zS0ZrJTB4rXiDmzmM6Cg1K kShPU1otYba2SFM568CPgXlYR6vFYlrNXYvgo6jzF13GwooYkEUxrgvAEQnGaeSsETsPqxicxduRV rr9zueqRHvX1CP3NoFIs5eWyEvSXxt7GWoDtXEZ6LFtS2Y8kiyUvgn8XGz8rDfbQ9M+f93YQLMywm iF74YcMw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1ljG8A-00EhnQ-Vh; Wed, 19 May 2021 06:56:38 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 8593D30021B; Wed, 19 May 2021 08:56:33 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 65F4B2027BB36; Wed, 19 May 2021 08:56:33 +0200 (CEST) Date: Wed, 19 May 2021 08:56:33 +0200 From: Peter Zijlstra To: Josh Poimboeuf Cc: linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Ingo Molnar , x86@kernel.org, willy@infradead.org, masahiroy@kernel.org, michal.lkml@markovi.net Subject: Re: [tip: objtool/core] jump_label, x86: Allow short NOPs Message-ID: References: <20210506194158.216763632@infradead.org> <162082558708.29796.10992563428983424866.tip-bot2@tip-bot2> <20210518195004.GD21560@worktop.programming.kicks-ass.net> <20210518202443.GA48949@worktop.programming.kicks-ass.net> <20210519004411.xpx4i6qcnfpyyrbj@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210519004411.xpx4i6qcnfpyyrbj@treble> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 18, 2021 at 07:44:11PM -0500, Josh Poimboeuf wrote: > I'm not exactly thrilled that objtool now has the power to easily brick > a system :-/ Is it really worth it? The way I look at it is that not running objtool is a bug either way, bricking a system is ofcourse a somewhat more drastic failure mode than missing ORC info for example, but neither are good. As to worth, about half the jump labels are shorter now, this reduces I$ pressure on hot paths. Any little thing to offset the ever increasing bulk seems like a good thing to me. But yes, it would be nice if the assemblers wouldn't suck so bad and this wouldn't need objtool :/ But I've tried poking the tools guys and they don't really seem interested :-( Also, only dirty builds are affected here; clean builds (always recommended afaik, because dep trouble isn't unheard of) are fine. > Anyway, here's one way to fix it. Maybe Masahiro has a better idea. Thanks! lemme go read up on this magic :-)