time: prevent the loop in timespec_add_ns() from being optimised away

Since some architectures don't support __udivdi3().

Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/time.h b/include/linux/time.h
index b04136d60a..3e8fd9e57e 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -173,6 +173,10 @@ static inline void timespec_add_ns(struct timespec *a, u64 ns)
 {
         ns += a->tv_nsec;
         while(unlikely(ns >= NSEC_PER_SEC)) {
+                /* The following asm() prevents the compiler from
+                 * optimising this loop into a modulo operation.  */
+                asm("" : "+r"(ns));
+
                 ns -= NSEC_PER_SEC;
                 a->tv_sec++;
         }