From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755097AbXD2JZ2 (ORCPT ); Sun, 29 Apr 2007 05:25:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755093AbXD2JZ2 (ORCPT ); Sun, 29 Apr 2007 05:25:28 -0400 Received: from smtp1.linux-foundation.org ([65.172.181.25]:47718 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755090AbXD2JZ1 (ORCPT ); Sun, 29 Apr 2007 05:25:27 -0400 Date: Sun, 29 Apr 2007 02:24:40 -0700 From: Andrew Morton To: bbpetkov@yahoo.de Cc: Andy Whitcroft , linux-kernel@vger.kernel.org, Jeremy Fitzhardinge Subject: Re: [PATCH] mm/memory.c: remove warning from an uninitialized spinlock. was: Re: 2.6.21-rc7-mm2 Message-Id: <20070429022440.cb8fc8c4.akpm@linux-foundation.org> In-Reply-To: <20070429065049.GB4446@gollum.tnic> References: <20070425225716.8e9b28ca.akpm@linux-foundation.org> <20070426182519.GA4532@gollum.tnic> <20070427172230.94b82829.akpm@linux-foundation.org> <4633DD55.1020006@shadowen.org> <20070429065049.GB4446@gollum.tnic> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 29 Apr 2007 08:50:49 +0200 Borislav Petkov wrote: > Introduce a macro for suppressing gcc from generating a warning about a probable > unitialized state of a variable. I ended up doing the below. It's better to make this a per-compiler-version thing: later versions of gcc might need different tricks, or might provide __attribute__((stfu)) or whatever. Plus I don't know if the x=x trick is needed on the intel compiler, nor if it even works, so I left ICC alone. From: Borislav Petkov Introduce a macro for suppressing gcc from generating a warning about a probable uninitialized state of a variable. Example: - spinlock_t *ptl; + spinlock_t *uninitialized_var(ptl); Not a happy solution, but those warnings are obnoxious. - Using the usual pointlessly-set-it-to-zero approach wastes several bytes of text. - Using a macro means we can (hopefully) do something else if gcc changes cause the `x = x' hack to stop working - Using a macro means that people who are worried about hiding true bugs can easily turn it off. Signed-off-by: Borislav Petkov Signed-off-by: Andrew Morton --- include/linux/compiler-gcc3.h | 6 ++++++ include/linux/compiler-gcc4.h | 6 ++++++ include/linux/compiler-intel.h | 2 ++ 3 files changed, 14 insertions(+) diff -puN include/linux/compiler-gcc3.h~add-unitialized_var-macro-for-suppressing-gcc-warnings include/linux/compiler-gcc3.h --- a/include/linux/compiler-gcc3.h~add-unitialized_var-macro-for-suppressing-gcc-warnings +++ a/include/linux/compiler-gcc3.h @@ -13,4 +13,10 @@ #define __must_check __attribute__((warn_unused_result)) #endif +/* + * A trick to suppress uninitialized variable warning without generating any + * code + */ +#define uninitialized_var(x) x = x + #define __always_inline inline __attribute__((always_inline)) diff -puN include/linux/compiler-gcc4.h~add-unitialized_var-macro-for-suppressing-gcc-warnings include/linux/compiler-gcc4.h --- a/include/linux/compiler-gcc4.h~add-unitialized_var-macro-for-suppressing-gcc-warnings +++ a/include/linux/compiler-gcc4.h @@ -16,3 +16,9 @@ #define __must_check __attribute__((warn_unused_result)) #define __compiler_offsetof(a,b) __builtin_offsetof(a,b) #define __always_inline inline __attribute__((always_inline)) + +/* + * A trick to suppress uninitialized variable warning without generating any + * code + */ +#define uninitialized_var(x) x = x diff -puN include/linux/compiler-intel.h~add-unitialized_var-macro-for-suppressing-gcc-warnings include/linux/compiler-intel.h --- a/include/linux/compiler-intel.h~add-unitialized_var-macro-for-suppressing-gcc-warnings +++ a/include/linux/compiler-intel.h @@ -22,3 +22,5 @@ (typeof(ptr)) (__ptr + (off)); }) #endif + +#define uninitialized_var(x) x _