From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758312Ab2D0HzB (ORCPT ); Fri, 27 Apr 2012 03:55:01 -0400 Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:59811 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753491Ab2D0Hy7 (ORCPT ); Fri, 27 Apr 2012 03:54:59 -0400 Message-ID: <4F9A50BD.1090000@openvz.org> Date: Fri, 27 Apr 2012 11:54:37 +0400 From: Konstantin Khlebnikov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.2) Gecko/20120217 Firefox/10.0.2 Iceape/2.7.2 MIME-Version: 1.0 To: Andrew Morton CC: Linus Torvalds , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , Hugh Dickins Subject: Re: [PATCH 1/4] compiler.h: introduce unused_expression() macro References: <20120425112623.26927.43229.stgit@zurg> <20120426153411.8686e0f9.akpm@linux-foundation.org> In-Reply-To: <20120426153411.8686e0f9.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > On Wed, 25 Apr 2012 15:26:23 +0400 > Konstantin Khlebnikov wrote: > >> Sometimes we want to check some expressions correctness in compile-time without >> generating extra code. "(void)(e)" does not work if expression has side-effects. >> This patch introduces macro unused_expression() which helps in this situation. >> >> Cast to "long" required because sizeof does not work for bit-fields. >> >> Signed-off-by: Konstantin Khlebnikov >> --- >> include/linux/compiler.h | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/include/linux/compiler.h b/include/linux/compiler.h >> index 923d093..46fbda3 100644 >> --- a/include/linux/compiler.h >> +++ b/include/linux/compiler.h >> @@ -310,4 +310,6 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); >> */ >> #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) >> >> +#define unused_expression(e) ((void)(sizeof((__force long)(e)))) >> + > > btw, please let's not add undocumented stuff, particularly obscure > undocumented stuff. > > I typed this in: Thanks! > > --- a/include/linux/compiler.h~compilerh-introduce-unused_expression-macro-fix > +++ a/include/linux/compiler.h > @@ -310,6 +310,11 @@ void ftrace_likely_update(struct ftrace_ > */ > #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) > > +/* > + * unused_expression() permits the compiler to check the validity of the > + * expression but avoids the generation of any code, even if that expression > + * has side-effects. > + */ > #define unused_expression(e) ((void)(sizeof((__force long)(e)))) > > #endif /* __LINUX_COMPILER_H */ > > but then decided I didn't want to apply the patches (yet?). I'm OK with that. But probably Hugh Dickins (now in CC) aggressively wants to remove side-effects of VM_BUG_ON's in case CONFIG_DEBUG_VM=n > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/