linux-kernel - Re: [PATCH v3 1/2] docs: add a document about regression handling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <12e09497-a848-b767-88f4-7dabd8360c5e@leemhuis.info>
Date:   Wed, 2 Feb 2022 12:46:27 +0100
From:   Thorsten Leemhuis <linux@...mhuis.info>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        workflows@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>,
        regressions@...ts.linux.dev,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: Re: [PATCH v3 1/2] docs: add a document about regression handling

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 <linux@...mhuis.info> 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 <src>/arch/<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