Re: [Xen-devel] [PATCH] FIX: Cast the time_t values to avoid warnings

[7heo@xxxxxxx]

On Sat, Apr 27, 2013 at 11:03:49PM +0100, Patrick Welche wrote:
> On Sat, Apr 27, 2013 at 11:32:35PM +0200, 7heo@xxxxxxx wrote:
> > On Sat, Apr 27, 2013 at 09:18:03PM +0100, Patrick Welche wrote:
> > > On Sat, Apr 27, 2013 at 09:52:33PM +0200, 7heo wrote:
> > > > I added 4 casts from time_t to unsigned long int
> > > > in the libxl_sprintf functions, so there is no
> > > > warning at compilation time (and no failing with
> > > > -Werror).
> > > > 
> > > > The casting format has been discuted, and since
> > > > there is no system having a 8 byte time_t format
> > > > yet; unsigned long int should be sufficient.
> > > > Also, it matches the libxl_sprintf syntax (%lu).
> > > 
> > > I thought that earlier in the thread someone pointed
> > > out that unsigned long long would be a better plan?
> > > (long could just be 32 bits long)
> > > 
> > > Cheers,
> > > 
> > > Patrick
> > 
> > As explained in the second paragraph of the git commit
> > message (even if I did a typo); this has been discussed
> > already.
> 
> Is the typo in the part which says "since there is no system having
> a 8 byte time_t format yet", which should read "most systems which
> want to keep going beyond 2038 have 8 byte time_t format"?
> The box I'm sitting in front of certainly has sizeof(time_t)==8.
> 
> The point is that all that is guaranteed is that
>   sizeof(long long) >= sizeof(long) >= sizeof(int)
> 
> Just checked on a 32-bit OS:
> 
> % cat foo.c
> #include <stdio.h>
> #include <time.h>
> 
> int main()
> {
>   printf("time_t: %u  int: %u  long: %u  long long: %u\n",
>     sizeof(time_t), sizeof(int), sizeof(long), sizeof(long long));
> 
>   return 0;
> }
> % ./foo
> time_t: 8  int: 4  long: 4  long long: 8
> 
> so long long is a better choice.
> 
> 
> Cheers,
> 
> Patrick

Thanks for having taken the time to check. Then it would
maybe make sense to check the size of time_t at
compilation time (with cpp instructions) in order to
chose the cast that fits, wouldn't it?

Also, this surprises me, I wouldn't have imagined that
people would care about the 32bit time overflow before
2035...

Regards,
7heo.


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