Re: [PATCH 2/6] nptl: Convert tst-cond11.c to use libsupport

[Mike Crowe <mac at mcrowe dot com>]

On Wednesday 03 April 2019 at 09:18:56 +0700, Adhemerval Zanella wrote:
> On 29/03/2019 01:31, Mike Crowe wrote:
> > diff --git a/support/timespec.h b/support/timespec.h
> > new file mode 100644
> > index 0000000..d439d62
> > --- /dev/null
> > +++ b/support/timespec.h
> > @@ -0,0 +1,115 @@
[...]
> > +static inline void
> > +timespec_sub (struct timespec *diff, const struct timespec *left,
> > +	      const struct timespec *right)
> > +{
> > +  diff->tv_sec = left->tv_sec - right->tv_sec;
> > +  diff->tv_nsec = left->tv_nsec - right->tv_nsec;
> > +
> > +  if (diff->tv_nsec < 0)
> > +    {
> > +      --diff->tv_sec;
> > +      diff->tv_nsec += 1000000000;
> > +    }
> > +}
> > +
> 
> I think we should handle overflow in such tests and assuming always signed
> time_t we can use a simplified version of gnulib (if I get everything right):
> 
> ---
> void
> timespec_subtract (struct timespec *r, const struct timespec *a,
>                    const struct timespec *b)
> { 
>   time_t rs = a->tv_sec;
>   time_t bs = b->tv_sec;
>   long int ns = a->tv_nsec - b->tv_nsec;
>   long int rns = ns;
>   
>   if (ns < 0)
>     { 
>       rns = ns + TIMESPEC_HZ;
>       if (bs < TYPE_MAXIMUM (time_t))
>         bs++;
>       else
>         {  
>           rs = TYPE_MINIMUM (time_t);
>           rns = 0;
>         }
>    }
>   
>   if (!__builtin_sub_overflow (rs, bs, &rs))
>     rs -= bs;
>   else
>     { 
>       if (rs < 0)
>         {  
>           rs = TYPE_MINIMUM (time_t);
>           rns = 0;
>         }
>       else 
>         {  
>           rs = TYPE_MAXIMUM (time_t);
>           rns = TIMESPEC_HZ - 1;
>         }
>     }
> 
>   *r = (struct timespec) { ns, rns };
> }

That seems to rely on macros from include/intprops.h anyway, so is there
any disadvantage in just using the gnulib version as it stands (along with
a suitable definition of TIMESPEC_HZ)?

But, having said that, this code from gnulib is GPLv3 (and it always has
been), whereas glibc is LGPLv2.1. Surely this means that we can't just copy
the code across?

Mike.