Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751025AbdHaGxD (ORCPT ); Thu, 31 Aug 2017 02:53:03 -0400 Received: from relay2-d.mail.gandi.net ([217.70.183.194]:33711 "EHLO relay2-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750711AbdHaGxC (ORCPT ); Thu, 31 Aug 2017 02:53:02 -0400 X-Originating-IP: 209.85.215.54 MIME-Version: 1.0 In-Reply-To: <878ti08oru.fsf@concordia.ellerman.id.au> References: <20170829230114.11662-1-joe@ovn.org> <20170830155910.4e2d43b92ff2d1e4492965d0@linux-foundation.org> <878ti08oru.fsf@concordia.ellerman.id.au> From: Joe Stringer Date: Wed, 30 Aug 2017 23:52:39 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] compiler: Don't perform compiletime_assert with -O0. To: Michael Ellerman Cc: Andrew Morton , LKML , Ian Abbott , Arnd Bergmann , Michal Nazarewicz , Kees Cook Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1633 Lines: 35 On 30 August 2017 at 19:16, Michael Ellerman wrote: > Joe Stringer writes: > >> On 30 August 2017 at 15:59, Andrew Morton wrote: >>> On Tue, 29 Aug 2017 16:01:14 -0700 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". >>> >>> I'm wondering if we should backport this into -stable. Probably not, >>> as I doubt if many people use -O0 - it's a pretty weird thing to do. I >>> used to use it a bit because it makes the ".lst" files (intermingled .c >>> and .s files) make more sense. In fact I'm wondering how you even >>> noticed this? >> >> Local debugging, was trying to get a better understanding of the >> underlying assembly and the code I was using just happened to use >> container_of(). > > Does the kernel actually build with -O0? I didn't think it actually > worked. I haven't tried the whole kernel, but you can set these CFLAGS on specific files with a one-liner in a makefile: CFLAGS_foo.o = -O0