From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754809AbZHMPti (ORCPT ); Thu, 13 Aug 2009 11:49:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751545AbZHMPth (ORCPT ); Thu, 13 Aug 2009 11:49:37 -0400 Received: from smtp-4.hut.fi ([130.233.228.94]:40190 "EHLO smtp-4.hut.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750951AbZHMPth (ORCPT ); Thu, 13 Aug 2009 11:49:37 -0400 X-Greylist: delayed 1020 seconds by postgrey-1.27 at vger.kernel.org; Thu, 13 Aug 2009 11:49:36 EDT Date: Thu, 13 Aug 2009 18:32:11 +0300 (EEST) From: Jan Wagner X-X-Sender: jwagner@orbit.lan To: linux-kernel@vger.kernel.org Subject: 32-bit sys/times.h incorrect return value (fwd) Message-ID: User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-TKK-Virus-Scanned: by amavisd-new-2.1.2-hutcc at katosiko.hut.fi Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, we see times() return a really large positive value like 0x66693CF1 i.e. signed int32 +1718172913 just a few minutes after booting. Note that clock_gettime(CLOCK_MONOTONIC) works correctly and returns the uptime. While times() +1718172913/100Hz time is in no relation to uptime. Checking 'man 2 times': "Since Linux 2.6, this point is (2^32/HZ) - 300 (i.e., about 429 million) seconds before system boot time. [...] the returned value may overflow the range of clock_t [...]" Hence in theory on a 32-bit platform where clock_t is signed 32-bit, at first times() should return negative values. Then 300 seconds later they should become positive. Correct? This should also happen via glibc times() call. There the times() ./sysdeps/unix/sysv/linux/times.c simply does clock_t ret = INTERNAL_SYSCALL (times, err, 1, buf); with no extra "+- some constant". In the kernel all jiffies and times syscall related handling is 64-bit: --------- amn@multics:/home/etu/Desktop/linux-2.6.30.3/include$ fgrep INITIAL_JIFFIES linux/jiffies.h:#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ)) kernel/sys.c: return (long) jiffies_64_to_clock_t(get_jiffies_64()); kernel/time.c:u64 get_jiffies_64(void) kernel/time.c: ret = jiffies_64; --------- On 32-bit platforms and signed int32 clock_t it should take at least octave:1> 2^31/(24*60*60 * 100) ans = 248.55 octave:2> (2^31/100 - 300)/(24*60*60) ans = 248.55 days until the positive times() return value wraps back to smallest negative signed 32-bit int. However, two bugs(?) : 1) times() return value after 1080 'uptime' seconds is 0x66693CF1, why? Expected value would be (1080-300)*100Hz = 78000 = 0x000130B0 ! 2) the times() wraps to negative only after 50 days uptime. Following the intention of INITIAL_JIFFIES, how is this 50-day warp supposed to reveal wrapping bugs right at 300 seconds after boot? 2) on 64-bit platforms, clock_t is 64-bit. There times() does not wrap after 50 days, however it still starts at 0x000000006669**** !? Any ideas? - Jan