linux-kernel - Re: [PATCH 0/3] tracepoints: delay argument evaluation

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Message-Id: <1242805127.26820.532.camel@twins>
Date:	Wed, 20 May 2009 09:38:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Roland McGrath <roland@...hat.com>
Cc:	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, mingo@...e.hu, laijs@...fujitsu.com,
	rostedt@...dmis.org, mathieu.desnoyers@...ymtl.ca,
	jiayingz@...gle.com, mbligh@...gle.com, fche@...hat.com
Subject: Re: [PATCH 0/3] tracepoints: delay argument evaluation

On Wed, 2009-05-20 at 00:27 -0700, Roland McGrath wrote:
> > Why can't 
> > 
> > trace_block_bio_complete(arg..)
> >    if (__trace_block_bio_compete.state)
> >      __trace_block_bio_complete(arg)
> > 
> > work?
> > 
> > Surely its possible to wrap the whole stuff in yet another macro layer
> > that will do the conditional before evaluating the arguments?
> 
> That is exactly what Jason has implemented.  
> He called the new macro layer tracepoint_call.
> 
> You can't use a macro to generate a new macro definition, so it's not
> possible with cpp alone to have the new macro layer be one that defines a
> separate trace_foobar() macro for each defined tracepoint.

Right, just realized that.

But I think we should be asking GCC to get fixed. Since inline functions
don't act like a compiler barrier anyway, they might as well not force
argument evaluation either.
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