From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759341Ab2I2B0K (ORCPT ); Fri, 28 Sep 2012 21:26:10 -0400 Received: from nm38-vm6.bullet.mail.bf1.yahoo.com ([72.30.239.22]:23771 "HELO nm38-vm6.bullet.mail.bf1.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1758342Ab2I2B0I (ORCPT ); Fri, 28 Sep 2012 21:26:08 -0400 X-Yahoo-Newman-Id: 962794.94240.bm@omp1007.access.mail.mud.yahoo.com X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: Y3nQXuoVM1nEgKxKoHhnif17SuT9RswcUnBtl57dNW9Pu7T k82u4LZ.FkPwdzgXvokFDpszTe2fowyyISD7Vt7.Ljjey75RmazZjgbeQkRy GGZwVjkKI6mNogbeN2RvYiYuV6HL2BP33.N.0muKQKV.DJ7udEX1KCkc6jEb VVCSAlrPdyCGbaby9RI3Gcetrh7nNIbJBFrQ17PUVG.BqwYbhztTneKVEykT Ql5pgF0wUZ8F0eckPP99V55eXrVUovAJnghLjotvtu3_Glf.EKgYzL1BG4cR sxaYkPCAkkEZeugq9rct7bPrCWxVno5XGOBPiVx1m5opS04UGhk1i.1IBcJV nFn2R6YYxA6TvYYwwU9phv3oBXZPuCrB5ULPq8ajXGsk8sNW0ZqzCkdVB.NX n4WYRJo5Yf5QgNEgAKG9L4XkOZo3_bWrar1BYHPjpodAnINL7BA-- X-Yahoo-SMTP: xXkkXk6swBBAi.5wfkIWFW3ugxbrqyhyk_b4Z25Sfu.XGQ-- Message-ID: <50664E30.7050809@att.net> Date: Fri, 28 Sep 2012 20:26:08 -0500 From: Daniel Santos Reply-To: Daniel Santos User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.4) Gecko/20120502 Thunderbird/10.0.4 MIME-Version: 1.0 To: Josh Triplett CC: Daniel Santos , LKML , Andi Kleen , Andrea Arcangeli , Andrew Morton , Christopher Li , David Daney , David Howells , Joe Perches , Konstantin Khlebnikov , linux-sparse@vger.kernel.org, Michel Lespinasse , Paul Gortmaker , Pavel Pisa , Peter Zijlstra , Steven Rostedt Subject: Re: [PATCH 8/10] bug.h: Make BUILD_BUG_ON generate compile-time error References: <1348874411-28288-1-git-send-email-daniel.santos@pobox.com> <1348874411-28288-9-git-send-email-daniel.santos@pobox.com> <20120929003239.GA14293@jtriplet-mobl1> In-Reply-To: <20120929003239.GA14293@jtriplet-mobl1> X-Enigmail-Version: 1.3.5 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/28/2012 07:32 PM, Josh Triplett wrote: > On Fri, Sep 28, 2012 at 06:20:09PM -0500, Daniel Santos wrote: >> Negative sized arrays wont create a compile-time error in some cases >> starting with gcc 4.4 (e.g., inlined functions), but gcc 4.3 introduced >> the error function attribute that will. This patch modifies >> BUILD_BUG_ON to behave like BUILD_BUG already does, using the error >> function attribute so that you don't have to build the entire kernel to >> discover that you have a problem, and then enjoy trying to track it down >> from a link-time error. > > Rather than doing both, and potentially producing two errors for the > same issue, how about using __compiletime_error only, and only using the > negative-sized array when __compiletime_error has no useful definition? > > For instance, in compiler.h, when defining __compiletime_error as an > empty macro in the fallback case, you could define a > __compiletime_error_fallback() macro that declares a negative-sized > array; you could then define __compiletime_error_fallback() as an empty > macro when it doesn't exist. It may also make sense to define #define BUILD_BUG() BUILD_BUG_ON(1) I haven't examined this really closely yet and my eyes are getting a little bleary :) Really, I would have liked to be able to set the error message as well, but we would have to have the macro generate a unique function name for each time its expanded to make that work. Example: #define BUILD_BUG_ON(cond) BUILD_BUG_ON_MSG(cond, #cond) #define BUILD_BUG_ON_MSG(cond, msg) \ do { \ extern void __build_bug_on_failed ## something_unique(void)\ __compiletime_error("BUILD_BUG_ON failed: " msg); \ __compiletime_error_fallback(cond); \ if (cond) \ __build_bug_on_failed(); \ } while(0) I just don't know any tricks to generate unique pre-processor value automatically. Daniel