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Message-ID: <863e9df20801032234v1a0eba9arfc71098a100bb145@mail.gmail.com>
Date: Fri, 4 Jan 2008 12:04:35 +0530
From: "Abhishek Sagar" <sagar.abhishek@gmail.com>
To: "Masami Hiramatsu" <mhiramat@redhat.com>
Subject: Re: [PATCH] x86: kprobes change kprobe_handler flow
Cc: "Ingo Molnar" <mingo@elte.hu>,
       "Harvey Harrison" <harvey.harrison@gmail.com>,
       "H. Peter Anvin" <hpa@zytor.com>, LKML <linux-kernel@vger.kernel.org>,
       "Thomas Gleixner" <tglx@linutronix.de>, qbarnes@gmail.com,
       ananth@in.ibm.com, jkenisto@us.ibm.com
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On 1/4/08, Masami Hiramatsu <mhiramat@redhat.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@redhat.com, masami.hiramatsu.pt@hitachi.com

Thanks,
Abhishek Sagar
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