Re: [RFA/sparc64] internal-error printing return value (Ada array)

Joel Brobecker
2006-11-12T21:55:35Z

> Hmm, I gueass I should have asked how a gdb `struct type' looks for
> these Ada arrays? In particular, if main_type->nfields is set and
> whether main_type->fields is set to something useful.

Ah, I understand now (sorry). Yes, main_type->nfields is 1, and
main_type->fields contains the bounds.

> > > You should also check how small arrays are passed as arguments to a
> > > function.
> >
> > This is described by the Ada Reference Manual: Arrays are always
> > passed by reference. So a function taking a parameter of our static
> > array type will have the array passed by reference. As a result,
> > the the array parameter will be a REF to a TYPE_CODE_ARRAY.
>
> So there is no way to pass a TYPE_CODE_ARRAY directly?

Not as a parameter for a function or procedure, no.

> > > Here the magic length will be 16 bytes instead of 32 bytes.
> >
> > I don't understand this part. Why 16 bytes instead of 32?
> > If the total size of the array is 32 bytes, shouldn't the compiler
> > return it through %o0 - %o7?
>
> The 16-byte limit is for passing structures as an argument to a function.
> I presume this is because function arguments occupy 16-byte slots in the
> ABI.

Ah, OK, I think I see where you are going. I failed to notice that
the function I modified is also used for storing/extracting function
parameters.

In terms of the argument passing, we don't need to worry in our case,
because arrays are passed by reference. In terms of a return value,
the ABI says that structs of up to 32 bytes can be returned.

3.2.3.3. Structure or Union return values

Structure and union return types up to thirty-two bytes in size
are returned in registers. The registers are assigned as if the
value was being passed as the first argument to a function with
a known prototype.

This is why I used the magic number of 32 in this case. I still think
it is correct, although more comments are certainly required to explain
the above.

What do you think?
--
Joel