Re: [PATCH v2 1/2] linux: Normalize and return timeout on select (BZ #27651)

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella via Libc-alpha:

> +/* Return true if select modify the timeout to reflect the amount of time
> +   no slept.  */
> +extern bool support_select_modify_timeout (void);
> +
> +/* Return true if select normalize the timeout input by taking in account
> +   tv_usec larger than 1000000.  */
> +extern bool support_select_normalize_timeout (void);

Maybe use support_select_modifies_timeout and
support_select_normalizes_timeout?

Please commit the support/ bits separately.

> diff --git a/sysdeps/unix/sysv/linux/select.c b/sysdeps/unix/sysv/linux/select.c
> index 415aa87d3c..d075270ff4 100644
> --- a/sysdeps/unix/sysv/linux/select.c
> +++ b/sysdeps/unix/sysv/linux/select.c
> @@ -33,12 +33,34 @@ int
>  __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
>  	    struct __timeval64 *timeout)
>  {
> +  __time64_t s = timeout != NULL ? timeout->tv_sec : 0;
> +  int32_t us = timeout != NULL ? timeout->tv_usec : 0;
> +  int32_t ns;
> +
> +  if (s < 0 || us < 0)
> +    return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
> +
> +  /* Normalize the timeout, as legacy Linux __NR_select and __NR__newselect.
> +     Different than syscall, it also handle possible overflow.  */
> +  if (us / USEC_PER_SEC > INT64_MAX - s)
>      {
> +      s = INT64_MAX;
> +      ns = NSEC_PER_SEC - 1;
>      }
> +  else
> +    {
> +      s += us / USEC_PER_SEC;
> +      us = us % USEC_PER_SEC;
> +      ns = us * NSEC_PER_USEC;
> +    }
> +
> +  struct __timespec64 ts64, *pts64 = NULL;
> +   if (timeout != NULL)
> +     {
> +       ts64.tv_sec = s;
> +       ts64.tv_nsec = ns;
> +       pts64 = &ts64;
> +     }

The overflow handling is slightly inconsistent with the in_time_t_range
range check below.  Here we use silently saturating arithmetic, below
it's an error.

Thanks,
Florian