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

c7dcf87a · John Stultz <[email protected]> · 2010-08-13 11:30:58 -07:00

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 <[email protected]>
CC: Jason Wessel <[email protected]>
CC: Larry Finger <[email protected]>
CC: Ingo Molnar <[email protected]>
CC: Linus Torvalds <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: c7dcf87a6881bf796faee83003163eb3de41a309
Parents: 2be1f3a7

Changes

1 files changed · +4 −3

File	Status	Add	Del	Content
kernel/time/timekeeping.c	modified	+4	−3	View file

kernel/time/timekeeping.c

View file

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e960d82..49010d8 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -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;
 