linux-kernel - Re: [PATCH 1/23] Make register values available to panic notifiers

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Message-ID: <20100412153557.42b3155a@mschwide.boeblingen.de.ibm.com>
Date:	Mon, 12 Apr 2010 15:35:57 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Russell King <rmk@....linux.org.uk>
Cc:	David VomLehn <dvomlehn@...co.com>, to@...mlehn-lnx2.corp.sa.net,
	"linux-arch@...r.kernel.org"@cisco.com, linux-arch@...r.kernel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	maint_arch@...mlehn-lnx2.corp.sa.net
Subject: Re: [PATCH 1/23] Make register values available to panic notifiers

On Mon, 12 Apr 2010 13:27:45 +0100
Russell King <rmk@....linux.org.uk> wrote:

> On Sun, Apr 11, 2010 at 11:06:09PM -0700, David VomLehn wrote:
> > This patch makes panic() and die() registers available to, for example,
> > panic notifier functions.  Panic notifier functions are quite useful
> > for recording crash information, but they don't get passed the register
> > values. This makes it hard to print register contents, do stack
> > backtraces, etc. The changes in this patch save the register state when
> > panic() is called and introduce a function for die() to call that allows
> > it to pass in the registers it was passed.
> 
> Can you explain why you want this?
> 
> I'm wondering about the value of saving the registers; normally when a panic
> occurs, it's because of a well defined reason, and not because something
> went wrong in some CPU register; to put it another way, a panic() is a
> more controlled exception than a BUG() or a bad pointer dereference.

I'm curious about the potential use case as well. So far I only wanted
to know the registers if the panic has been triggered due to an
unexpected fault with panic_on_oops=1 or in_interrupt()==1. If that
happens the die() handler prints the registers. An open coded panic is
easy to analyze, imho no need for the registers.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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