Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754100AbdHXQ7I convert rfc822-to-8bit (ORCPT ); Thu, 24 Aug 2017 12:59:08 -0400 Received: from slow1-d.mail.gandi.net ([217.70.178.86]:35931 "EHLO slow1-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753634AbdHXQ7H (ORCPT ); Thu, 24 Aug 2017 12:59:07 -0400 X-Originating-IP: 209.85.215.46 MIME-Version: 1.0 In-Reply-To: <20170824164506.9108-1-joe@ovn.org> References: <20170824164506.9108-1-joe@ovn.org> From: Joe Stringer Date: Thu, 24 Aug 2017 09:49:13 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH net-next] compiler: Document behavior compiling with -O0 To: LKML Cc: Ian Abbott , Arnd Bergmann , Michal Nazarewicz , Kees Cook 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 Content-Length: 1924 Lines: 35 On 24 August 2017 at 09:45, Joe Stringer wrote: > Recent changes[0] to make use of __compiletime_assert() from container_of() > increased the scope of this macro, resulting in a wider set of > situations where developers cannot compile their code using "-O0". I > noticed this when making use of the macro in my own development, and > spent more time than I'd like to admit tracking the problem down. This > patch documents the behavior in lieu of a compile-time assertion > implementation that does not rely on optimizations. > > 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 This patch was written against the net-next tree, but is not targeted at the net-next tree. My usual submissions go there so my formatting scripts just inserted that. I can strip out and resend against a particular tree if this is a problem.