linux-kernel - Re: [PATCH] x86: push old stack address on irqstack for unwinder

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Message-ID: <49838F39.6060603@zytor.com>
Date:	Fri, 30 Jan 2009 15:37:29 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Martin Hicks <mort@....com>
CC:	tglx@...utronix.de, mingo@...hat.com, heukelum@...lshack.com,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: push old stack address on irqstack for unwinder

Martin Hicks wrote:
> Hi,
> 
> KDB was using this information.  Could this be pushed towards 2.6.29 please?
> 
> This re-adds the old stack pointer to the top of the irqstack to help
> with unwinding.  It was removed in commit d99015b1abbad743aa049b439c1e1dede6d0fa49
> as part of the save_args out-of-line work.
> 

This bothers me... why should we add even a single instruction to what 
is arguably the single hottest path in the kernel to support an 
out-of-tree debugger, especially if kgdb (which is in-tree) doesn't need it?

What does kgdb do differently (or is kgdb broken too)?

	-hpa
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