Re: [RFC/RFA] gdb extension for Harvard architectures

[Michael Snyder <msnyder@redhat.com>]

Jim Blandy wrote:
> 
> Michael Snyder <msnyder@cygnus.com> writes:
> > > Should these spaces be flags or an enumeration?  I don't think being
> > > able to specify space = (CODE | DATA) is meanginful.  Haveing bit masks
> > > also puts a limitation on the number of spaces.
> >
> > Yes, but it's a generous limitation (there are 20 more bits available).
> > I'll go either way -- the trade-off is that if we don't use the "flags"
> > field, we have to add a new field to the (struct type) data
> > structure.
> 
> (This is a suggested enhancement to Michael's patch; I think it's a
> step forward as is.)
> 
> Instead of using bits, what if we added a new `const char *' field to
> `struct type'?  Its value would be a string indicating the name of the
> space qualifier applied to the type, or zero indicating the default.

Just to make sure I understand you, the string you propose is
something like "code", not the fully qualified type eg. "code int *";
right?


> The set of permitted space names would be determined by the
> architecture, following some basic conventions (like `data' and
> `code').  There would be a gdbarch method like this:
> 
> - int gdbarch_valid_addr_space_name_p (struct gdbarch *A, const char *NAME);
>   Return non-zero if NAME is a valid name of an address space
>   for architecture A.
> 
> The parser would recognize `@ IDENTIFIER' as a space qualifier, call
> gdbarch_valid_addr_space_name_p to check it, and drop the value into
> the type it creates if so.
> 
> The type printer would simply printf ("@%s", type->space); when printing.
> 
> There would be a core function:
> 
> - const char *type_default_addr_space (struct type *T);
>   Return "code" if T is a pointer to function or method; return "data"
>   otherwise.
> 
> The POINTER_TO_ADDRESS and ADDRESS_TO_POINTER methods, which are the
> ones who actually *use* this info, receive the type object already,
> and can check the space as appropriate.

OK, the reason I didn't do it like that (and I did consider it) is
  a) it required a new field in the type struct, and
  b) a strcmp takes longer than an integer (flag) test.

However, I agree that this might be a reasonable extension, 
especially once we get ready to let the target architecture
define its own address spaces.  I wanted to get a relatively
simple initial implementation approved before I went overboard
on complexity (it's complex enough as it is).

Michael