Re: IBM z/OS compatibility issues

[Daniel Richard G.]

(Apologies for the delayed response)

On Wed, 2019 Nov  6 14:32-05:00, Paul Eggert wrote:
> 
> IBM's user guide for the compiler 
> <https://www-01.ibm.com/servers/resourcelink/svc00100.nsf/pages/zOSV2R3sc147307/$file/cbcux01_v2r3.pdf>,
>  
> dated 2019-06-26, states the following on page 153:
> 
> "Until IBM's implementation of all the features of the C11 standard is
> complete,... IBM makes no attempt to maintain compatibility ... with
> earlier releases of IBM's implementation of the new features of the
> C11 standard and therefore they should not be relied on as a stable
> programming interface."

Ah, good find. I suspected that the compiler is in a transitional period
w.r.t. C11.

> With this in mind, perhaps it'd be better to use that compiler in its
> C99 mode, to avoid having 'configure' attempt to use C11 features
> before IBM gets its C11 act together. That should be good enough for
> now, and we can worry about getting Gnulib to work with IBM's C11
> support once that support is ready.

The C99 mode (-qlanglvl=extc99) works without issue. That's what I've
been using for all my testing.

> Although 'configure' does the right thing and says that _Alignas is 
> unsupported, 'make' then goes ahead and builds a stdalign.h that assumes 
> that _Alignas works (because the compiler defines __STDC_VERSION__ to be 
> 201112), and the generated stdalign.h therefore defines alignas and 
> __alignas_is_defined, which is wrong.

Hmm, I see what you mean. FWIW, the "checking for working stdalign.h"
check does end with "no".

> > What leaves me scratching my head is that in
> > /usr/include/stdalign.h, I see the following:
> > 
> >      #if defined(__C1X)
> >        #define alignas _Alignas
> >        #define alignof _Alignof
> >        #define __alignas_is_defined 1
> >        #define __alignof_is_defined 1
> >      #endif
> 
> So /usr/include/stdalign.h has the same bug as the Gnulib stdalign.h
> replacement, in that it also defines alignas and __alignas_is_defined
> even though _Alignas does not work. Presumably /usr/include/stdalign.h
> is relying on the statement in the manual that C11 support is still
> unstable and can't be relied upon.
>
> So it sounds like we should let this particular sleeping dog lie, as
> far as Gnulib is concerned.

I do get the feeling that the C11 brokenness of this compiler is not
worth working around. IBM is normally a stickler for standards, which
makes this an unusual scenario, but I think it's a good enough solution
for users who are bitten by this to press IBM to get it right. I
certainly plan on doing so.


--Daniel


-- 
Daniel Richard G. || address@hidden
My ASCII-art .sig got a bad case of Times New Roman.