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

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Date:	Tue, 29 Jan 2008 11:32:04 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Abhishek Sagar <sagar.abhishek@...il.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 Sun, Jan 27, 2008 at 02:38:56PM +0530, Abhishek Sagar wrote:
> Greetings,
> 
> Non kprobe breakpoints in the kernel might lie inside the .kprobes.text section. Such breakpoints can easily be identified by in_kprobes_functions and can be caught early. These are problematic and a warning should be emitted to discourage them (in any rare case, if they actually occur).

Why? As Masami indicated in an earlier reply, the annotation is to
prevent *only* kprobes.
 
> For this, a check can route the trap handling of such breakpoints away from kprobe_handler (which ends up calling even more functions marked as __kprobes) from inside kprobe_exceptions_notify.

Well.. we pass on control of a !kprobe breakpoint to the kernel. This is
exactly what permits debuggers like xmon to work fine now. I don't see
any harm in such breakpoints being handled autonomously without any sort
of kprobe influence.

Ananth
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