linux-kernel - Re: [git pull] kgdb-light -v9

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Message-Id: <20080212102636.02715270192@magilla.localdomain>
Date:	Tue, 12 Feb 2008 02:26:35 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ingo Molnar <mingo@...e.hu>, "Frank Ch. Eigler" <fche@...hat.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [git pull] kgdb-light -v9

> You silently overwrite any user ptrace hw breakpoints right? To do it cleanly 
> would still require a reservation frame work.

There was work underway on that before (hw_breakpoint).  I'm not entirely
sure you want to use fancy stuff like that in kgdb.  It's nice for kgdb to
be as self-contained as possible, so you can debug everything else with it.
If you're going to rely on lots of higher-level infrastructure, it could be
using kprobes for its software breakpoint handling, too.

At any rate, I think it would be good if the hw breakpoint support in kgdb
were chopped out into a separate patch.  First make kgdb work with no code
touching debug registers at all.  Then a second patch can add the hw
breakpoint support.  The latter one can be mulled over or replaced with a
hw_breakpoint merge or just put off for a while because it's a big can of
worms to multiplex the use of the debug registers.

Thanks,
Roland
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