Messages in this thread |  | | | Subject | Re: [PATCH 6/9][RFC] kprobes: Allow probe on ftrace reserved text (but move it) | | From | Steven Rostedt <> | | Date | Wed, 02 May 2012 19:40:32 -0400 |
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On Wed, 2012-05-02 at 16:40 -0400, Frank Ch. Eigler wrote: > rostedt wrote: > > > [...] Added KPROBE_FLAG_MOVED (as suggested by Masami) that is set > > when the address is moved to get around an ftrace nop. [...] > > Steve, perhaps my earlier comments on this got lost during the mailing > list outage.
I saw it, but it didn't really specify what you wanted. Here's your comment:
> I suspect Masami intended that this flag is later used during int3 > processing to subtract MCOUNT_INSN_SIZE back out from the pt_regs->ip > during kprobe_handler() if this flag was set.
This is what I thought too, but to me it sounded like Masami could do the work. I was just setting up a flag to make it possible.
> > The gist is that a KPROBE_FLAG_MOVED being set this way accomplishes > very little since nothing is looking for that flag. Instead, you > should patch {arch/*}/kernel/kprobe.c kprobe_handler() to subtract > MCOUNT_INSN_SIZE back out from pt_regs->ip if KPROBE_FLAG_MOVED was > set. That way, kprobes clients need do not perceive the int3 movement.
I basically thought that Masami wanted me to add the flag, and then others could look for this and do the adjustment. I'm not the kprobes author. I was just adding a flag that Masami and others could use to do such updates.
I'm not sure if the adjustment is fine with everyone, as it may cause repercussions that I don't know about.
Perhaps that could be another patch (want to write it?)
-- Steve
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