linux-kernel - Re: [RFC patch 3/5] ftrace trace event add missing semicolumn

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Message-ID: <20110105020759.GG2911@nowhere>
Date:	Wed, 5 Jan 2011 03:08:02 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC patch 3/5] ftrace trace event add missing semicolumn

On Tue, Jan 04, 2011 at 07:18:37PM -0500, Mathieu Desnoyers wrote:
> * Frederic Weisbecker (fweisbec@...il.com) wrote:
> > On Tue, Jan 04, 2011 at 06:16:32PM -0500, Mathieu Desnoyers wrote:
> > > Add a missing semicolumn at the end of a ftrace definition.
> > > 
> > > We currently are not seeing any impact of this missing semicolumn because extra
> > > semicolumns appear all over the place in the code generated from TRACE_EVENT
> > > within ftrace stages.
> > > 
> > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > > CC: Steven Rostedt <rostedt@...dmis.org>
> > > CC: Frederic Weisbecker <fweisbec@...il.com>
> > > CC: Ingo Molnar <mingo@...e.hu>
> > > CC: Thomas Gleixner <tglx@...utronix.de>
> > > ---
> > >  include/trace/ftrace.h |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > Index: linux-2.6-lttng/include/trace/ftrace.h
> > > ===================================================================
> > > --- linux-2.6-lttng.orig/include/trace/ftrace.h
> > > +++ linux-2.6-lttng/include/trace/ftrace.h
> > > @@ -69,7 +69,7 @@
> > >  #undef DEFINE_EVENT
> > >  #define DEFINE_EVENT(template, name, proto, args)	\
> > >  	static struct ftrace_event_call	__used		\
> > > -	__attribute__((__aligned__(4))) event_##name
> > > +	__attribute__((__aligned__(4))) event_##name;
> > 
> > But DEFINE_EVENT() calls are supposed to be ";" terminated, no?
> 
> Currently yes, but if you look at the preprocessor output currently generated by
> the current TRACE_EVENT()/DEFINE_EVENT() scheme, there are useless ";" added all
> over the place. I have a patch later in my queue that proposes removal of these
> extra ";" as a cleanup of the TRACE_EVENT() semantic, but I'm keeping it for
> later because it removes the extra ";" at the end of each TRACE_EVENT()
> instance (and thus is more intrusive code-wise).
> 
> Adding this semicolumn here ensures that all Ftrace macros are consistent wrt
> semicolumns. We can get away without consistency currently exactly because the
> current scheme adds many useless semicolumns between each TRACE_EVENT().

Are you sure you want to put so much time on this?

This will require a massive change for the sole win of removing double ";"
in generated code. This won't optimize much the build, and it will make the things
not so much more readable for very rare people who dare to have interest into the
TRACE_EVENT generated code. That notwithstanding the obfuscation of that generated
code resides more in the lack of indentation and newlines than in double
semicolons that we barely notice.

Hm?
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