linux-kernel - Re: [PATCH 0/3][RFC] x86: Catch stray non-kprobe breakpoints

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Date:	Tue, 29 Jan 2008 22:54:46 +0530
From:	"Abhishek Sagar" <sagar.abhishek@...il.com>
To:	ananth@...ibm.com
Cc:	LKML <linux-kernel@...r.kernel.org>, jkenisto@...ibm.com,
	"Masami Hiramatsu" <mhiramat@...hat.com>,
	"Ingo Molnar" <mingo@...e.hu>
Subject: Re: [PATCH 0/3][RFC] x86: Catch stray non-kprobe breakpoints

On 1/29/08, Ananth N Mavinakayanahalli <ananth@...ibm.com> wrote:
> > May be I'm completely off the mark here, but shouldn't a small subset
> > of this section simply be 'breakpoint-free' rather than 'kprobe-free'?
> > Placing a breakpoint on kprobe_handler (say) can loop into a recursive
> > trap without allowing the debugger's notifier chain to be invoked.
>
> A well heeled debugger will necessarily take care of saving contexts
> (using techniques like setjmp/longjmp, etc) to help it recover from such
> nested cases (See xmon for example).

Ok, but the protection/warning is not just for xmon.

> > I'm assuming that non-kprobe exception notifiers may (or even should) run
> > after kprobe's notifier callback (kprobe_exceptions_notify).
>
> Yes, any such notifier is invoked after kprobe's callback as the kprobe
> notifier is always registered with the highest priority.

Ok.

> > The WARN_ON (and not a BUG_ON) will be hit iff:
> > (in_kprobes_functions(addr) && !is_jprobe_bkpt(addr))
>
> But that still is unneeded dmesg clutter, IMHO.

Ok, a warning in my opinion would've been prudent since I think we
cannot guarantee non kprobe breakpoint users (debuggers or anything
else) from the recursive trap handling case.

> Ananth

--
Thanks,
Abhishek
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