linux-kernel - Re: [PATCH] Kprobes: Add kprobes smoke tests that run on boot

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Message-Id: <1199918039.4162.40.camel@dyn9047018096.beaverton.ibm.com>
Date:	Wed, 09 Jan 2008 14:33:58 -0800
From:	Jim Keniston <jkenisto@...ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	ananth@...ibm.com, akpm@...ux-foundation.org,
	lkml <linux-kernel@...r.kernel.org>, mingo@...e.hu,
	mhiramat@...hat.com, davem@...emloft.net, hskinnemoen@...el.com
Subject: Re: [PATCH] Kprobes: Add kprobes smoke tests that run on boot

On Wed, 2008-01-09 at 22:21 +0100, Andi Kleen wrote:
> On Wed, Jan 09, 2008 at 12:24:00PM -0800, Jim Keniston wrote:
> > On Wed, 2008-01-09 at 00:28 +0100, Andi Kleen wrote:
> > > > I have no problem with that, but if we want to make it buildable as a
> > > > module, the call to get_kprobe() needs to be replaced with some other
> > > > gcc-inline-defeating mechanism, or we need to export get_probe().  I
> > > 
> > > It's still unclear where noinline does not work (do you have details on that? 
> > > It sounds a little dubious) ...
> > 
> > Here's a simplified version of a module we've used to gauge kprobes
> > performance.  On my system (i386, 2.6.23-rc8 at the moment, gcc version
> > 4.1.2), the module calls the (empty) probed function (probeme) niter
> > times, but reports zero probe hits -- indicating probeme was inlined
> > even though it was declared noinline.
> 
> Yes indeed looks like a gcc bug. Have you reported it?
> 
> -Andi

There's already a gcc bug report that appears to describe the same
problem:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34563
There seems to be some doubt as to whether it's really a bug, so I added
my 2 cents, including a pointer to this thread.

Jim 

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