Re: [RFC v3 2/3] sys/types.h: struct timespec: Use __snseconds_t for tv_nsec

[Joseph Myers <joseph@codesourcery.com>]

On Wed, 8 Dec 2021, Zack Weinberg wrote:

> On Wed, Dec 8, 2021, at 9:47 AM, Alejandro Colomar wrote:
> >
> > Use __snseconds_t to simplify the definition of struct timespec.
> ...
> >  #if __WORDSIZE == 64 \
> >    || (defined __SYSCALL_WORDSIZE && __SYSCALL_WORDSIZE == 64) \
> >    || (__TIMESIZE == 32 && !defined __USE_TIME_BITS64)
> > -  __syscall_slong_t tv_nsec;	/* Nanoseconds.  */
> > +  __snseconds_t tv_nsec;  /* Nanoseconds.  */
> 
> All my grousing about spec bugs aside, the _point_ of having tv_nsec's 
> type be a typedef is that it ought to be possible to make this 
> preprocessor conditional (and the rest of the cases in the same if-else 
> chain) less hairy.  Can you look into that please?

The question about whether there is padding around tv_nsec is a separate 
one to what the type of tv_nsec is.  I don't see how you can avoid the 
conditionals related to padding, which is what these conditionals are 
about.  And the preprocessor doesn't readily lend itself to saying "if 
tv_sec is 64-bit and tv_nsec is 32-bit" to describe when padding is 
involved.

-- 
Joseph S. Myers
joseph@codesourcery.com