linux-kernel - Re: [PATCH] x86: kprobes remove fix

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Message-ID: <4777B0AA.9050503@redhat.com>
Date:	Sun, 30 Dec 2007 09:52:26 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
CC:	Harvey Harrison <harvey.harrison@...il.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86: kprobes remove fix_riprel #ifdef

Hello Ingo,

Ingo Molnar wrote:
> * Masami Hiramatsu <mhiramat@...hat.com> wrote:
> 
>> Hello Harvey,
>>
>> A similar idea was already nack-ed by Ananth.
>> http://sources.redhat.com/ml/systemtap/2007-q4/msg00468.html
>> And I agree his thought.
>>
>> Especially, "riprel" does not exist on x86_32, so fix_riprel()
>> is meaningless on it.
>> Thus, I think it would better be ifdef'd in call-site.
> 
> but we regularly do this in generic code: we add calls that are NOPs on 
> some architectures. For example flush_cache_page() makes no sense on the 
> x86 architecture.

Indeed.
By the way, flush_cache_page() is defined as a do-while(0) on x86.
Would it better to define fix_riprel() as a do-while(0) on x86-32?
I think this obviously indicates that function has no effect.

> So i'm inclined to apply Harvey's cleanup - less
> #ifdef complexity in higher-level code is very much favored, even
> if "riprel" is a NOP concept on 32-bit.

OK, I agree about that fix_riprel() which is ifdef'd twice is too much ifdef'd.
Reducing ifdef is good to me.

Thanks,
> 
> 	Ingo

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com, masami.hiramatsu.pt@...achi.com

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