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

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Message-ID: <20110105031016.GI2911@nowhere>
Date:	Wed, 5 Jan 2011 04:10:18 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Valdis.Kletnieks@...edu
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	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 10:01:33PM -0500, Valdis.Kletnieks@...edu wrote:
> On Wed, 05 Jan 2011 03:08:02 +0100, Frederic Weisbecker said:
> > On Tue, Jan 04, 2011 at 07:18:37PM -0500, Mathieu Desnoyers wrote:
> 
> > > > > --- 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;
> 
> > > 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.
> 
> Can DEFINE_EVENT ever be sensibly used in a context where the additional ; will
> cause an issue (for instance, a hypothetical array initialization like:
> 
> static struct events[] = {DEFINE_EVENT(..), DEFINE_EVENT(...) }

You can't do the above as DEFINE_EVENT() do more than just creating a structure.
It can define functions and so.

Plus it doesn't behave the same whether CREATE_TRACE_POINTS is defined or not:
it can either define or declare the functions and structures.
 
> or other places we usually do the 'do { X } while (0)' trick to make the code legal?

I just can't figure out a sane case.

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