linux-kernel - Re: [PATCH] CodingStyle: Add a chapter on conditional compilation

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Date:	Wed, 29 Oct 2014 19:24:11 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Jonathan Corbet <corbet@....net>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] CodingStyle: Add a chapter on conditional compilation

On Wed, Oct 29, 2014 at 05:35:02PM -0700, Randy Dunlap wrote:
> On 10/29/14 12:12, Geert Uytterhoeven wrote:
> > On Wed, Oct 29, 2014 at 7:15 PM, Josh Triplett <josh@...htriplett.org> wrote:
> >> Document several common practices and conventions regarding conditional
> >> compilation, most notably the preference for ifdefs in headers rather
> >> than .c files.
> >>
> >> Signed-off-by: Josh Triplett <josh@...htriplett.org>
> > 
> >> +If you have a function or variable which may potentially go unused in a
> >> +particular configuration, and the compiler would warn about its definition
> >> +going unused, mark the definition as __maybe_unused rather than wrapping it in
> >> +a preprocessor conditional.  (However, if a function or variable *always* goes
> >> +unused, delete it.)
> > 
> > Personally, I don't like __maybe_unused. Once it's there, the compiler
> > will stop warning about it, even if it really becomes unused.
> > 
> > Apart from that:
> > Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> 
> Is the compiler smart enough to delete (discard) the code or data instance
> if it is unused or is the code or data actually wasting space?

If you mark a function or variable as __maybe_unused, and it actually
goes unused, the compiler will silently discard it.

- Josh Triplett
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