Re: Ada gdb failures on hppa

[Daniel Jacobowitz <drow at false dot org>]

On Sat, Dec 31, 2005 at 10:56:17AM +0400, Joel Brobecker wrote:
> > I wonder what would happen is we changed the STRUCT_CONVENTION into
> > RETURN_VALUE_ABI_RETURNS_ADDRESS... I'll experiment quickly (have to
> > run soon) but I have suspicions that messy things might happen :-/.
> 
> I won't have time to test the following simple-minded patch, but it
> seems to be doing the trick for this specific case. It basically looks
> like the return_value methods of hppa needs to be enhanced to know how
> to retrive values returned by address...
> 
> I'll finish having a look next week if I have time, but don't hesitate
> to take over if you want. I think the hppa64 part will be identical,
> so perhaps isolating this in a function and then call this new function
> from both hppa32 and hppa64 return_value methods will fix the problem
> for both ABIs.

It's pretty unlikely that this change is safe - it's likely to work for
simple functions, but not for more complex ones.  Do you have an ABI
document to back this up?  Specifically these comments in defs.h:

  /* Like the "struct return convention" above, but where the ABI
     guarantees that the called function stores the address at which
     the value being returned is stored in a well-defined location,
     such as a register or memory slot in the stack frame.  Don't use
     this if the ABI doesn't explicitly guarantees this.  */
  RETURN_VALUE_ABI_RETURNS_ADDRESS,
  /* Like the "struct return convention" above, but where the ABI
     guarantees that the address at which the value being returned is
     stored will be available in a well-defined location, such as a
     register or memory slot in the stack frame.  Don't use this if
     the ABI doesn't explicitly guarantees this.  */
  RETURN_VALUE_ABI_PRESERVES_ADDRESS,

[Mark, you added these.  Could you explain the difference between the
two?  There's no target using RETURN_VALUE_ABI_PRESERVES_ADDRESS, and
I completely don't understand what the difference is supposed to be.
They're always handled the same way, too.]

> +      const CORE_ADDR val_addr = read_register (HPPA_RET0_REGNUM);

This function takes a regcache, you should use it :-)

-- 
Daniel Jacobowitz
CodeSourcery, LLC