linux-kernel - Re: [PATCH] x86: kprobes change kprobe

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Message-ID: <863e9df20801032234v1a0eba9arfc71098a100bb145@mail.gmail.com>
Date:	Fri, 4 Jan 2008 12:04:35 +0530
From:	"Abhishek Sagar" <sagar.abhishek@...il.com>
To:	"Masami Hiramatsu" <mhiramat@...hat.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Harvey Harrison" <harvey.harrison@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>, qbarnes@...il.com,
	ananth@...ibm.com, jkenisto@...ibm.com
Subject: Re: [PATCH] x86: kprobes change kprobe_handler flow

On 1/4/08, Masami Hiramatsu <mhiramat@...hat.com> wrote:
> I could understand what the original code did at last.
> If a kprobe is inserted on a breakpoint which other debugger inserts,
> it single step inline instead of out-of-line.(this is done in prepare_singlestep)
> In this case, (p && kprobe_running() && kcb->kprobe_status==KPROBE_HIT_SS)
> is true and we need pass the control to the debugger.
> And if (*p->ainsn.insn != BREAKPOINT_INSTRUCTION) (or (p != kprobe_running())) in
> that case, there may be some bugs.

Yes, we can only fault while singlestepping for a unique case, which
is when we're singlestepping (in-line) a breakpoint because a probe
was installed on it. All other scenarios are a BUG . That's also
assuming that no exception will preempt singlestepping, whose codepath
has a probe on it.

> Now I think your original suggestion is correct.
> Please fix it in another patch.

Ok.

> --
> Masami Hiramatsu
>
> Software Engineer
> Hitachi Computer Products (America) Inc.
> Software Solutions Division
>
> e-mail: mhiramat@...hat.com, masami.hiramatsu.pt@...achi.com

Thanks,
Abhishek Sagar
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