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time: Workaround gcc loop optimization that causes 64bit div errors 

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>
This commit is contained in:
John Stultz 2010-08-13 11:30:58 -07:00 committed by Linus Torvalds
parent 2be1f3a73d
commit c7dcf87a68
1 changed files with 4 additions and 3 deletions
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7
kernel/time/timekeeping.c
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@ -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;