On Wed, Jul 10, 2019 at 03:01:53PM +0200, Arnd Bergmann wrote:
> On 32-bit x86 when building with clang-9, the loop gets turned back into
> an inefficient division that causes a link error:
> 
> kernel/time/vsyscall.o: In function `update_vsyscall':
> vsyscall.c:(.text+0xe3): undefined reference to `__udivdi3'
> 
> Use the provided __iter_div_u64_rem() function that is meant to address
> the same case in other files.
> 
> Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() 
> implementation")
> Signed-off-by: Arnd Bergmann <a...@arndb.de>
> ---
>  kernel/time/vsyscall.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
> index a80893180826..8cf3596a4ce6 100644
> --- a/kernel/time/vsyscall.c
> +++ b/kernel/time/vsyscall.c
> @@ -104,11 +104,7 @@ void update_vsyscall(struct timekeeper *tk)
>       vdso_ts->sec    = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
>       nsec            = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift;
>       nsec            = nsec + tk->wall_to_monotonic.tv_nsec;
> -     while (nsec >= NSEC_PER_SEC) {
> -             nsec = nsec - NSEC_PER_SEC;
> -             vdso_ts->sec++;
> -     }
> -     vdso_ts->nsec   = nsec;
> +     vdso_ts->sec    += __iter_div_u64_rem(nsec, NSEC_PER_SEC, 
> &vdso_ts->nsec);
>  
>       if (__arch_use_vsyscall(vdata))
>               update_vdso_data(vdata, tk);
> -- 
> 2.20.0
> 

What an interesting function. Looks good to me and I can confirm it
fixes the link error.

Reviewed-by: Nathan Chancellor <natechancel...@gmail.com>
Tested-by: Nathan Chancellor <natechancel...@gmail.com>

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