Re: [PATCH] Export _NCPUWORDS as variable for access from within the gnat-rts

[Joel Sherrill <joel at rtems dot org>]

On 10/29/2015 9:20 AM, Jan Sommer wrote:
> Am Thursday 29 October 2015, 08:45:57 schrieb Joel Sherrill:
> > On 10/29/2015 8:14 AM, Jan Sommer wrote:
> > > Hi,
> > >
> > > This patch will make the define _NCPUWORDS accessible for the ada runtime. It is necessary to model the pthread_attr_t implementation for rtems  in Ada.
> > > We had a stack corruption because the C an Ada declarations of the type where out of synch.
> > > I will send the updated s-osinte-rtems.ads to  gcc if this patch is accepted.
> > >
> > > I put devel@rtems.org CC for input from the rtems developers.
> >
> > Is it possible to define this in the RTEMS Ada glue file?
>
> What is the rtems Ada glue file?

There are two support files in cpukit/libgnat. I looked through
the git log history of these files and it is quite boring. But
there isn't much code here, it is target independent, and might
be worth a double check. Better that than debugging something
else.

There is also some BSP specific code to map exceptions into
Ada exceptions. Some is in libbsp/shared. From memory, the sparc
BSPs have the exception propagation glue.

> Just to clarify: The problem I had was that pthread_attr_t has a field of
>
> typedef struct _cpuset {
>    cpu_set_word_t __bits[_NCPUWORDS];
> } cpu_set_t;
>
> which's length depends on _NCPUWORDS.
> In ada I added types like this:
>
>     NUMCPUWORDS : constant size_t;
>
>     pragma Import (
>        Convention    => C,
>        Entity        => NUMCPUWORDS,
>        External_Name => "_ADA_NCPUWORDS"
>     );
>
>     type cpu_set_array is array (0 .. NUMCPUWORDS) of
>        aliased cpu_set_word_t;
>
>     type cpu_set_t is record
>         bits : aliased cpu_set_array;
>     end record;
>
> I just put it into newlib, because I thought the export should be close to the original declaration.
> If you can point to a better fitting location I am happy to put it there.

There are a handful of similar cases handled in libgnat.
You have to have real C variables or methods to use
macros.

> Best regards,
>
>     Jan
>
> > Generally, I like the Ada support to be self-contained and
> > have no impact on anything else. This puts an Ada specific
> > variable in generic code.
> >
> > This is similar to how I had to do the Ada task minimum
> > stack size. It could have gone in more common code but
> > nothing else uses it so should not be impacted.
> >
> > Plus newlib doesn't know anything about our Ada glue layer.
> > Best to keep it that way.
> >
> > > Best regards,
> > >
> > >       Jan
>
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--
Joel Sherrill, Ph.D.
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