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Date: Tue, 9 Aug 2016 07:49:40 +0900
From: Masami Hiramatsu <mhiramat@kernel.org>
To: David Long <dave.long@linaro.org>
Cc: Daniel Thompson <daniel.thompson@linaro.org>,
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Subject: Re: [PATCH v15 04/10] arm64: Kprobes with single stepping support
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On Mon, 8 Aug 2016 10:29:05 -0400
David Long <dave.long@linaro.org> wrote:

> >> @@ -489,20 +477,15 @@ int __kprobes setjmp_pre_handler(struct kprobe
> >> *p, struct pt_regs *regs)
> >>  {
> >>      struct jprobe *jp = container_of(p, struct jprobe, kp);
> >>      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> >> -    long stack_ptr = kernel_stack_pointer(regs);
> >>
> >>      kcb->jprobe_saved_regs = *regs;
> >>      /*
> >> -     * As Linus pointed out, gcc assumes that the callee
> >> -     * owns the argument space and could overwrite it, e.g.
> >> -     * tailcall optimization. So, to be absolutely safe
> >> -     * we also save and restore enough stack bytes to cover
> >> -     * the argument area.
> >> +     * Since we can't be sure where in the stack frame "stacked"
> >> +     * pass-by-value arguments are stored we just don't try to
> >> +     * duplicate any of the stack.
> >  > ...
> >>                                       Do not use jprobes on functions
> >> that
> >> +     * use more than 64 bytes (after padding each to an 8 byte boundary)
> >> +     * of arguments, or pass individual arguments larger than 16 bytes.
> >
> > I like this wording. So much so that it really would be great to repeat
> > this in the Documentation/. Could this be included in the list of
> > architecture support/restrictions?
> >
> 
> Are you thinking specifically of the "5. Kprobes Features and 
> Limitations" section in Documentation/kprobes.txt?

OK, That's a good idea :)

If you update the patch for that, please feel free to add my Ack.

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>