From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765056AbYEAV5a (ORCPT ); Thu, 1 May 2008 17:57:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761443AbYEAV5X (ORCPT ); Thu, 1 May 2008 17:57:23 -0400 Received: from smtp4.pp.htv.fi ([213.243.153.38]:57600 "EHLO smtp4.pp.htv.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761216AbYEAV5W (ORCPT ); Thu, 1 May 2008 17:57:22 -0400 Date: Fri, 2 May 2008 00:56:33 +0300 From: Adrian Bunk To: "Pallipadi, Venkatesh" Cc: David Miller , trini@kernel.crashing.org, mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, "Siddha, Suresh B" , Linus Torvalds Subject: huge gcc 4.1.{0,1} __weak problem Message-ID: <20080501215633.GU29330@cs181133002.pp.htv.fi> References: <20080430013108.GA18207@linux-os.sc.intel.com> <20080429.212833.192304794.davem@davemloft.net> <924EFEDD5F540B4284297C4DC59F3DEEF7D18E@orsmsx423.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <924EFEDD5F540B4284297C4DC59F3DEEF7D18E@orsmsx423.amr.corp.intel.com> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 30, 2008 at 05:49:46AM -0700, Pallipadi, Venkatesh wrote: > > >-----Original Message----- From: David Miller > >From: Venki Pallipadi Date: Tue, 29 > >Apr 2008 18:31:09 -0700 > > > >> Some flavors of gcc 4.1.0 and 4.1.1 seems to have trouble > >understanding > >> weak function definitions. Calls to function from the same > >file where it is > >> defined as weak _may_ get inlined, even when there is a > >non-weak definition of > >> the function elsewhere. I tried using attribute 'noinline' > >which does not > >> seem to help either. > >> > >> One workaround for this is to have weak functions defined in > >different > >> file as below. Other possible way is to not use weak > >functions and go back > >> to ifdef logic. > >> > >> There are few other usages in kernel that seem to depend on > >weak (and noinline) > >> working correctly, which can also potentially break and > >needs such workarounds. > >> Example - > >> mach_reboot_fixups() in arch/x86/kernel/reboot.c is one such > >call which > >> is getting inlined with a flavor of gcc 4.1.1. > >> > >> Signed-off-by: Venkatesh Pallipadi > >> Signed-off-by: Suresh Siddha > > > >This sounds like a bug. And if gcc does multi-file compilation it > >can in theory do the same mistake even if you move it to another > >file. > > > >We need something more bulletproof here. > > > > The references here > http://gcc.gnu.org/ml/gcc-bugs/2006-05/msg02801.html > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27781 > > seem to suggest that the bug is only with weak definition in the same > file. > So, having them in a different file should be good enough workaround > here. >... A workaround here is the wrong solution since this isn't the only place that suffers from this issue. We currently give a #warning for 4.1.0. But not for 4.1.1. (Accordingto the bug >= 4.1.2 is fixed.) And a #warning is not enough. The huge problem is that "empty __weak function in the same file and non-weak arch function" has recently become a common pattern with several new usages added during this merge window alone. And the breakages can be very subtle runtime breakages. I see only the following choices: - remove __weak and replace all current usages - move all __weak functions into own files, and ensure that also happens for future usages - #error for gcc 4.1.{0,1} > Thanks, > Venki cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed