linux-kernel - Re: [RFC PATCH -tip 00/16] in-kernel x86 disassember

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Date:	Tue, 3 Apr 2012 09:31:45 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Masami Hiramatsu <masami.hiramatsu@...il.com>,
	linux-kernel@...r.kernel.org, Huang Ying <ying.huang@...el.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Jason Wessel <jason.wessel@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC PATCH -tip 00/16] in-kernel x86 disassember


* H. Peter Anvin <hpa@...or.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
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