From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936234AbYEBVKT (ORCPT ); Fri, 2 May 2008 17:10:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756283AbYEBVKF (ORCPT ); Fri, 2 May 2008 17:10:05 -0400 Received: from gw.goop.org ([64.81.55.164]:50619 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754423AbYEBVKD (ORCPT ); Fri, 2 May 2008 17:10:03 -0400 Message-ID: <481B8321.1000305@goop.org> Date: Fri, 02 May 2008 14:09:53 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Adrian Bunk CC: "Pallipadi, Venkatesh" , 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: Re: huge gcc 4.1.{0,1} __weak problem References: <20080430013108.GA18207@linux-os.sc.intel.com> <20080429.212833.192304794.davem@davemloft.net> <924EFEDD5F540B4284297C4DC59F3DEEF7D18E@orsmsx423.amr.corp.intel.com> <20080501215633.GU29330@cs181133002.pp.htv.fi> In-Reply-To: <20080501215633.GU29330@cs181133002.pp.htv.fi> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Adrian Bunk wrote: > 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} > - make __weak also include noinline. I think that's sufficient (at least it was when I encountered a gcc bug with these symptoms last year or so). J