Messages in this thread Patch in this message | | | Date | Tue, 24 Aug 2010 15:45:26 -0700 | From | Greg KH <> | Subject | [081/114] time: Workaround gcc loop optimization that causes 64bit div errors |
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2.6.35-stable review patch. If anyone has any objections, please let us know.
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From: John Stultz <johnstul@us.ibm.com>
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@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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- 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;
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