Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761375Ab0HMIpd (ORCPT ); Fri, 13 Aug 2010 04:45:33 -0400 Received: from fanny.its.uu.se ([130.238.4.241]:8112 "EHLO fanny.its.uu.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755902Ab0HMIpc (ORCPT ); Fri, 13 Aug 2010 04:45:32 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <19557.1573.852727.108838@pilspetsen.it.uu.se> Date: Fri, 13 Aug 2010 10:45:25 +0200 From: Mikael Pettersson To: Larry Finger Cc: Linus Torvalds , Jason Wessel , John Stultz , LKML Subject: Re: Problem with commit deda2e81961e96be4f2c09328baca4710a2fd1a0 In-Reply-To: <4C645C7D.1050903@lwfinger.net> References: <4C64571F.6000606@lwfinger.net> <4C645C7D.1050903@lwfinger.net> X-Mailer: VM 7.17 under Emacs 20.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2085 Lines: 51 Larry Finger writes: > On 08/12/2010 03:26 PM, Linus Torvalds wrote: > > On Thu, Aug 12, 2010 at 1:18 PM, Larry Finger wrote: > >> > >> With the above commit, building an i386 version of the kernel results in the > >> following from the build: > >> > >> kernel/built-in.o: In function `logarithmic_accumulation': > >> /home/finger/linux-realtek/kernel/time/timekeeping.c:715: undefined reference to > >> `__umoddi3' > >> /home/finger/linux-realtek/kernel/time/timekeeping.c:715: undefined reference to > >> `__udivdi3' > >> make: *** [.tmp_vmlinux1] Error 1 > >> > >> Reverting the patch allows the system to build correctly. > > > > Damn. It's your compiler turning a while-loop into a divide. Which > > likely isn't even an optimization, but whatever. > > > > John: I think that while-loop needs to be something like > > > > if (raw_nsecs >= NSEC_PER_SEC) { > > u64 raw_secs = raw_nsecs; > > raw_nsecs = do_div(raw_secs, NSEC_PER_SEC); > > raw_time.tv_sec += taw_secs; > > } > > raw_time.tc_nsec = raw_nsecs; > > > > which is sad and overly complicated, but the simple thing seems to get > > messed up by the compiler. > > > > Untested. Maybe I got the complex do_div() semantics wrong. Somebody > > needs to check. > > I'll try it. The system with the problem has gcc (SUSE Linux) 4.3.2 > [gcc-4_3-branch revision 141291]. That is on a 64-bit system cross compiling > with ARCH=i386. > > The real 32-bit system with gcc (SUSE Linux) 4.5.0 20100604 [gcc-4_5-branch > revision 160292] builds OK. It just wasn't finished when I wrote the first message. The loops-turns-into-div is a known bug in early gcc-4.3 releases, possibly only with -Os. It's fixed in 4.4 and 4.3.latest. I can probably dig up the gcc PR number if needed. /Mikael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/