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 329D6C433EF for ; Wed, 2 Feb 2022 11:46:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231171AbiBBLqb (ORCPT ); Wed, 2 Feb 2022 06:46:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32794 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234359AbiBBLqb (ORCPT ); Wed, 2 Feb 2022 06:46:31 -0500 Received: from wp530.webpack.hosteurope.de (wp530.webpack.hosteurope.de [IPv6:2a01:488:42:1000:50ed:8234::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CB916C061714; Wed, 2 Feb 2022 03:46:30 -0800 (PST) Received: from ip4d144895.dynamic.kabel-deutschland.de ([77.20.72.149] helo=[192.168.66.200]); authenticated by wp530.webpack.hosteurope.de running ExIM with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) id 1nFE5k-0006et-9U; Wed, 02 Feb 2022 12:46:28 +0100 Message-ID: <12e09497-a848-b767-88f4-7dabd8360c5e@leemhuis.info> Date: Wed, 2 Feb 2022 12:46:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Content-Language: en-BS To: Geert Uytterhoeven Cc: "open list:DOCUMENTATION" , Linus Torvalds , workflows@vger.kernel.org, Linux Kernel Mailing List , Jonathan Corbet , Randy Dunlap , regressions@lists.linux.dev, Greg Kroah-Hartman , Lukas Bulwahn References: From: Thorsten Leemhuis Subject: Re: [PATCH v3 1/2] docs: add a document about regression handling In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-bounce-key: webpack.hosteurope.de;linux@leemhuis.info;1643802390;286e733a; X-HE-SMSGID: 1nFE5k-0006et-9U Precedence: bulk List-ID: X-Mailing-List: workflows@vger.kernel.org Hi! I noticed I forgot to reply here: On 26.01.22 15:28, Geert Uytterhoeven wrote: > On Tue, Jan 25, 2022 at 5:45 PM Thorsten Leemhuis wrote: >> +How to create a configuration similar to the one of an older kernel? >> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> + >> +Start a known-good kernel and configure the newer Linux version with ``make >> +olddefconfig``. This makes the kernel's build scripts pick up the configuration >> +file (the `.config` file) from the running kernel as base for the new one you >> +are about to compile; afterwards they set all new configuration options to their >> +default value, which should disable new features that might cause regressions. > > Doing so may actually cause mutations to appear in your .config > when going back and forth (i.e. when bisecting), interfering with > the bisection process. Good point, I knew about this, but hadn't thought of this when writing the text. > To avoid that, I usually start bisecting with > "cp .config /arch//configs/bisect_defconfig", and use > "make bisect_defconfig" in every bisection step. That way all steps > are reproducible, and unaffected by config mutations. That's a really cool trick, thx for mentioning it. But I think it's not needed in the text about regressions and instead better be mentioned in Documentation/admin-guide/bug-bisect.rst. I hope to sooner or later improve (rewrite?) that document anyway and will make sure to keep it in mind for that time. I wonder if there is a way to make this work without messing in the source tree? Took a quick look at the sources. It seems to me that it's possible to "cp .config ~/working.config" and then using "make KBUILD_DEFCONFIG=~/working.config defconfig" at every bisection step. It seems to do the trick as well -- but I only tried briefly, so maybe I might have missed something. Ciao, Thorsten