Re: Last <sys/cdefs.h> change

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

On 05/23/2013 10:58 AM, Corinna Vinschen wrote:
> On May 23 10:03, Sebastian Huber wrote:
> > On 05/23/2013 09:44 AM, Corinna Vinschen wrote:
> > > On May 23 09:30, Sebastian Huber wrote:
> > > > Hello,
> > > >
> > > > what is the reason for the change:
> > > > [...]
> > > > There is already a test for C11 some lines above:
> > > >
> > > > #elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
> > > > /* Do nothing.  They are language keywords. */
> > > > #else
> > > > /* Not supported.  Implement them using our versions. */
> > > >
> > > > If you want C11 in GCC, you have to specify -std=c11 or -std=gnu11.
> > >
> > > gcc >= 4.6 defines _Static_assert even without -std=C11.
> > >
> > > See http://cygwin.com/ml/cygwin/2013-05/msg00310.html
> >
> > In this message the problem occurs with "gcc -std=gnu99".  Asking
> > for a C11 feature with such a command line seems to be
> > contradictory.
> >
> > I would use this approach:
> >
> > --- newlib/libc/include/sys/cdefs.h     2013-05-23 09:21:47.817952315 +0200
> > +++ cdefs.h     2013-05-23 10:01:28.014875569 +0200
> > @@ -261,15 +261,15 @@
> >   #define        _Thread_local           __thread
> >   #elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
> >   /* Do nothing.  They are language keywords. */
> > +#elif !defined(__STDC_VERSION__) && __GNUC_PREREQ__(4, 6)
> > +/* Do nothing.  They are provided for free. */
>
> Does that mean _Alignas, _Alignof, _Noreturn, and _Thread_local
> are also defined since 4.6?

Ok, this is a good question.  Sorry for sending such sloppy proposals.

> I don't quite grok the !defined(__STDC_VERSION__) here.  gcc 4.6 defines
> _Static_assert independently from the -std setting and independently
> from -ansi.  It's just there, always.  The coreutils header assumes that
> _Static_assert exists because it found that it's compiled with gcc 4.6
> or later.  It uses the _Static_assert in a way which works with the
> builtin version of gcc.  This collides with the definition of
> _Static_assert in cdefs.h.  Now, with your change, cdefs.h would fall
> back to its own definition again if __STDC_VERSION__ is defined, thus
> your change would break coreutils again.

The only broken thing here is coreutils.  They set -std=gnu99 and use C11 
features.  They use also _Static_assert() in a way that seems to be not 
available with pre C11 means.

I think now that your patch is perfect for this situation.  Since these defines 
are directly from the latest FreeBSD version this means that coreutils are also 
broken here (I guess nobody cares about this).

--
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschÃftliche Mitteilung im Sinne des EHUG.