[081/114] time: Workaround gcc loop optimization that causes 64bit div errors

[Greg KH]

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: John Stultz <johnstul@xxxxxxxxxx>

commit c7dcf87a6881bf796faee83003163eb3de41a309 upstream.

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@xxxxxxxxxx>
CC: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
CC: Larry Finger <Larry.Finger@xxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 kernel/time/timekeeping.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -756,9 +756,10 @@ static cycle_t logarithmic_accumulation(
 	/* 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;
 


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/