linux-kernel - Re: [PATCH 2.6.27-rc1-git5 2/26] mdb: correct kprobes int3 trap

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Date:	Wed, 6 Aug 2008 14:10:14 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	jmerkey@...fmountaingroup.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.27-rc1-git5 2/26] mdb: correct kprobes int3 trap

On Tue, Aug 05, 2008 at 12:26:35AM -0600, jmerkey@...fmountaingroup.com wrote:
...

> @@ -850,6 +871,10 @@
>  #ifdef CONFIG_KPROBES
>  void __kprobes do_int3(struct pt_regs *regs, long error_code)
>  {
> +#ifdef	CONFIG_MDB
> +        if (mdb(BREAKPOINT_EXCEPTION, error_code, regs))
> +           return;
> +#endif // CONFIG_MDB
>  	trace_hardirqs_fixup();
> 
>  	if (notify_die(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP)

Kprobes needs to be the first consumer of these exceptions (via
notify_die); if the exception was due to a kprobe, it does its thing
without requiring any user intervention. Here, for example, you can get
into mdb for a kprobe breakpoint hit.

Please move the mdb hooks to after kprobes has been notified. Better
still, integrate mdb to use the notify_die infrastructure and use a
lower priority than what kprobes does for it.

Ananth
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