linux-kernel - Re: [PATCH 3/4] x86: add kprobe-booster to X86

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Date:	Tue, 18 Dec 2007 21:21:34 -0800
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Roland McGrath <roland@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	prasanna@...ibm.com, anil.s.keshavamurthy@...el.com,
	davem@...emloft.net, systemtap-ml <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/4] x86: add kprobe-booster to X86_64

On Tue, 2007-12-18 at 23:43 -0500, Masami Hiramatsu wrote:
> Harvey Harrison wrote:
> > On Tue, 2007-12-18 at 08:50 -0500, Masami Hiramatsu wrote:
> >> Hi Harvey,
> >>
> >> Thank you for cleaning this up.
> >>
> >> Harvey Harrison wrote:
> >>> Subject: [PATCH] x86: kprobes leftover cleanups
> >>>
> >>> Eliminate __always_inline, all of these static functions are
> >>> only called once.  Minor whitespace cleanup.  Eliminate one
> >>> supefluous return at end of void function.  Reverse sense of
> >>> #ifndef to be #ifdef to show the case only affects X86_32.
> >> Unfortunately, to prevent kprobe recursive call, all functions which
> >> is called from kprobes must be inlined or have __kprobes.
> >> If __always_inline macro still work, I prefer to use it. If not,
> >> it must have a __kprobe attribute like as below.
> > 
> > I thought all static functions that were only called once were
> > automatically inlined these days?  Otherwise __always_inline and
> > inline are exactly the same in the kernel.
> 
> Yes, it will be (not obviously) inlined, currently.
> However, IMHO, it is not fail-safe coding.
> 

Fair enough, you seem to have a deeper understanding of the code than
I, I'd suggest __kprobes as a better annotation for this purpose though.

> I think we might better take care of someone who will modify the code
> in the future. If they call those functions from other place,
> it will not be inlined, and may be placed out of .kprobes.text.
> In that case, we can not prevent inserting kprobes in those functions.
> 
> Thus, I recommend you to add __kprobes on those functions.
> That indicates which functions will be used by kprobes and gives
> hints how to write functions which will be called from kprobes.
> (And also, it simplifies coding rule.)

Patch forthcoming.

Harvey

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