time: Workaround gcc loop optimization that causes 64bit div errors
authorJohn Stultz <johnstul@us.ibm.com>
Fri, 13 Aug 2010 18:30:58 +0000 (11:30 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 13 Aug 2010 19:03:24 +0000 (12:03 -0700)
Early 4.3 versions of gcc apparently aggressively optimize the raw
time accumulation loop, replacing it with a divide.

On 32bit systems, this causes the following link errors:
undefined reference to `__umoddi3'
undefined reference to `__udivdi3'

The gcc issue has been fixed in 4.4 and greater.

This patch replaces the accumulation loop with a do_div, as suggested
by Linus.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
CC: Jason Wessel <jason.wessel@windriver.com>
CC: Larry Finger <Larry.Finger@lwfinger.net>
CC: Ingo Molnar <mingo@elte.hu>
CC: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/time/timekeeping.c

index e960d824263f1d04aa17c5e256ec56a4cdfa5fd1..49010d822f725b47726742fa7e1b45aad076ef90 100644 (file)
@@ -710,9 +710,10 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
        /* Accumulate raw time */
        raw_nsecs = timekeeper.raw_interval << shift;
        raw_nsecs += raw_time.tv_nsec;
-       while (raw_nsecs >= NSEC_PER_SEC) {
-               raw_nsecs -= NSEC_PER_SEC;
-               raw_time.tv_sec++;
+       if (raw_nsecs >= NSEC_PER_SEC) {
+               u64 raw_secs = raw_nsecs;
+               raw_nsecs = do_div(raw_secs, NSEC_PER_SEC);
+               raw_time.tv_sec += raw_secs;
        }
        raw_time.tv_nsec = raw_nsecs;