From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758269AbaJ3CYY (ORCPT ); Wed, 29 Oct 2014 22:24:24 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:41267 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757684AbaJ3CYU (ORCPT ); Wed, 29 Oct 2014 22:24:20 -0400 X-Originating-IP: 50.43.41.112 Date: Wed, 29 Oct 2014 19:24:11 -0700 From: Josh Triplett To: Randy Dunlap Cc: Geert Uytterhoeven , Jonathan Corbet , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] CodingStyle: Add a chapter on conditional compilation Message-ID: <20141030022411.GA28982@thin> References: <430ce084b015d22a597ef7e4f6436dadaea7b23d.1414606455.git.josh@joshtriplett.org> <545187B6.1090704@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <545187B6.1090704@infradead.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 > > > >> +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 > > 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