From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752470AbdH3SDk convert rfc822-to-8bit (ORCPT ); Wed, 30 Aug 2017 14:03:40 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:41277 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751891AbdH3SDj (ORCPT ); Wed, 30 Aug 2017 14:03:39 -0400 X-Originating-IP: 209.85.215.45 MIME-Version: 1.0 In-Reply-To: References: <20170829230114.11662-1-joe@ovn.org> From: Joe Stringer Date: Wed, 30 Aug 2017 11:03:16 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] compiler: Don't perform compiletime_assert with -O0. To: Michal Nazarewicz Cc: LKML , Ian Abbott , Arnd Bergmann , Kees Cook , Andrew Morton Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30 August 2017 at 03:26, Michal Nazarewicz wrote: > On Tue, Aug 29 2017, Joe Stringer wrote: >> Recent changes[0] to make use of __compiletime_assert() from >> container_of() increased the usage of this macro, allowing developers to >> notice type conflicts in usage of container_of() at compile time. >> However, the implementation of __compiletime_assert relies on compiler >> optimizations to report an error. This means that if a developer uses >> "-O0" with any code that performs container_of(), the compiler will >> always report an error regardless of whether there is an actual problem >> in the code. >> >> This patch disables compile_time_assert when optimizations are disabled >> to allow such code to compile with CFLAGS="-O0". >> >> Example compilation failure: >> >> ./include/linux/compiler.h:547:38: error: call to ‘__compiletime_assert_94’ declared with attribute error: pointer type mismatch in container_of() >> _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) >> ^ >> ./include/linux/compiler.h:530:4: note: in definition of macro ‘__compiletime_assert’ >> prefix ## suffix(); \ >> ^~~~~~ >> ./include/linux/compiler.h:547:2: note: in expansion of macro ‘_compiletime_assert’ >> _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) >> ^~~~~~~~~~~~~~~~~~~ >> ./include/linux/build_bug.h:46:37: note: in expansion of macro ‘compiletime_assert’ >> #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) >> ^~~~~~~~~~~~~~~~~~ >> ./include/linux/kernel.h:860:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’ >> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \ >> ^~~~~~~~~~~~~~~~ >> >> [0] http://lkml.kernel.org/r/20170525120316.24473-7-abbotti@mev.co.uk >> >> Signed-off-by: Joe Stringer >> Cc: Ian Abbott >> Cc: Arnd Bergmann >> Cc: Michal Nazarewicz >> Cc: Kees Cook >> Cc: Andrew Morton >> --- >> include/linux/compiler.h | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/compiler.h b/include/linux/compiler.h >> index eca8ad75e28b..b67e5ec9b810 100644 >> --- a/include/linux/compiler.h >> +++ b/include/linux/compiler.h >> @@ -517,7 +517,8 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s >> # define __compiletime_error_fallback(condition) do { } while (0) >> #endif >> >> -#define __compiletime_assert(condition, msg, prefix, suffix) \ >> +#ifdef __OPTIMIZE__ >> +# define __compiletime_assert(condition, msg, prefix, suffix) \ >> do { \ >> bool __cond = !(condition); \ >> extern void prefix ## suffix(void) __compiletime_error(msg); \ >> @@ -525,6 +526,9 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s >> prefix ## suffix(); \ >> __compiletime_error_fallback(__cond); \ >> } while (0) >> +#else >> +# define __compiletime_assert(condition, msg, prefix, suffix) > > +# define __compiletime_assert(condition, msg, prefix, suffix) \ > + do { } while (0) > > With that fix, > > Acked-by: Michal Nazarewicz Thanks, I applied this change and send a v2 with your ack.