From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752288Ab2DCHbw (ORCPT <rfc822;w@1wt.eu>);
	Tue, 3 Apr 2012 03:31:52 -0400
Received: from mail-wg0-f44.google.com ([74.125.82.44]:54838 "EHLO
	mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751239Ab2DCHbu (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 3 Apr 2012 03:31:50 -0400
Date: Tue, 3 Apr 2012 09:31:45 +0200
From: Ingo Molnar <mingo@kernel.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Masami Hiramatsu <masami.hiramatsu@gmail.com>,
        linux-kernel@vger.kernel.org, Huang Ying <ying.huang@intel.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Jason Wessel <jason.wessel@windriver.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [RFC PATCH -tip 00/16] in-kernel x86 disassember
Message-ID: <20120403073145.GB26826@gmail.com>
References: <20120401160229.4502.2541.stgit@shimauta>
 <4F7A21B6.8000700@zytor.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4F7A21B6.8000700@zytor.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* H. Peter Anvin <hpa@zytor.com> wrote:

> On 04/01/2012 09:02 AM, Masami Hiramatsu wrote:
> > Hi,
> > 
> > Here is a series of patches of the in-kernel x86 disassembler
> > for the latest tip tree.
> > This will show you a pretty disassembled code instead of
> > just a digital code sequence when you gets a kernel panic etc.
> > (I know, we also have script/decodecode for the panic use)
> > 
> > This feature is not for users, but mainly for kernel developers
> > who can understand disassembly code of x86 ;). This is just like
> > a joke feature in kernel. (yeah, I spend my spare time for this.
> > It's my fun :))
> > 
> 
> This is cool, but I have one major reservation about it: it 
> will make kernel panics take a lot more screen real estate 
> without containing more information, and we already have 
> problems with things scrolling off way too easily.

Yes, I'm not sure we want to do it by default.

> For that reason I would like to request that this *only* 
> enabled by an explicit command-line option or similar 
> (disasm_oops, maybe?), so that the user has to opt-in.

The existing oops setup knob is an early_param() in 
kernel/panic.c, "oops=".

I'd suggesting extending that in an obvious way. Currently the 
only option that exists is "oops=panic", so a comma delimited 
list of attributes would be the natural extension, allowing:

	oops=panic
	oops=panic,disasm
	oops=disasm

Detail: it should do a strncmp(5, str, "disas"), so that every 
usual variant works: oops=disasm, oops=disassemble, etc.

> [...]  In other words, if *you* are debugging your own kernel, 
> and don't expect to ship oopses off to someone else.

Probably a DEBUG .config option as well, so that distros can 
enable it. OTOH, CONFIG_CMDLINE allows the setting of such 
parameters as well.

Thanks,

	Ingo