lkml.org 
[lkml]   [2010]   [Aug]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[081/114] time: Workaround gcc loop optimization that causes 64bit div errors
    2.6.35-stable review patch.  If anyone has any objections, please let us know.

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

    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;




    \
     
     \ /
      Last update: 2010-08-25 01:15    [W:0.022 / U:94.340 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site