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 473F2C11F67 for ; Tue, 29 Jun 2021 20:01:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2C4A861DAB for ; Tue, 29 Jun 2021 20:01:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234402AbhF2UEI (ORCPT ); Tue, 29 Jun 2021 16:04:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35658 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233961AbhF2UEF (ORCPT ); Tue, 29 Jun 2021 16:04:05 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 738EFC061760; Tue, 29 Jun 2021 13:01:37 -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=43EXmuxyFngAmR7da1cOLXA97ga+3kbzRG83psgM9Zg=; b=RbzmHRRMrMKfTKX7RoQERx1/qO pKXln50vJgqpCwaXzJIj17d7PPOwwzUme+3HAlQYvsUr4pxyxPDq7R+d3ezX8EDKt13sZh12NLqD/ H3QCe0vAy9NNdICFt3VMVLOJ/EjRR82pn3VX2mb/Sd94qEwJvHBpauaZDJLBSRTdflHeSsZvKkcCi C22+F6vcAasYXHQf/qlKZSK1G5DC2n75K0f+2nII3lzwoK9g2TcgopKmZ05AlvKxizlpT6QtxJA4S e0tGq1zQEPWcS0K+iAm96cSees3mTaMFOBtDdWbFNpAEhe61vqs2fHWh+DZklnW6cX0YgT/PIi5Vx smtIZmUg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1lyJuj-004UIj-PR; Tue, 29 Jun 2021 20:01:04 +0000 Date: Tue, 29 Jun 2021 21:00:57 +0100 From: Matthew Wilcox To: Peter Zijlstra Cc: Josh Poimboeuf , linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Ingo Molnar , x86@kernel.org, masahiroy@kernel.org, michal.lkml@markovi.net, Linus Torvalds 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: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org So this got merged without the corresponding Kbuild update being merged, and my kernel failed to boot. Bisect got as far as $ git bisect good Bisecting: 4 revisions left to test after this (roughly 2 steps) [ab3257042c26d0cd44793c741e2f89bf38b21fe8] jump_label, x86: Allow short NOPs before my sluggish memory remembered this thread from six weeks ago. So if anybody else hits this, do a make clean. On Wed, May 19, 2021 at 08:56:33AM +0200, Peter Zijlstra wrote: > 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 :-)