Re: REGISTER_BYTE() and pseudos

[Andrew Cagney <ac131313 at cygnus dot com>]

> OK, I see what you are doing.  Basically, if a pseudo maps onto a real 
> register somewhere in the regcache, you return the address of that.
> 
> However, what should be done if the pseudo doesn't exist as a single 
> entry, or if it is a manipulation of a real register?  For example, on the 
> ARM, the CPSR may be just a few bits retrieved from the PC.
> 
> Also, what would you do if you needed to address two non-adjacent 
> registers?

Return ``not_lval''.  I think that case can go in the too hard basket.

First, I don't know if GDB's ``struct value'' system is rich enough to 
describe a value split across [disjoint] registers and memory.  Second, 
even if it was, the current get_saved_register() doesn't make that 
knowledge available.  An interface more like value_of_register() would 
be better.

BTW, this code:

 > OK, I'll have another look.
 >
 > The bit I'm worried about though is if we call something like
 > generic_get_saved_register for a pseudo and we hit a call_dummy frame.
 > The code in there goes:
 >
 >       if (PC_IN_CALL_DUMMY (frame->pc, frame->frame, frame->frame))
 >         {
 >           if (lval)             /* found it in a CALL_DUMMY frame */
 >             *lval = not_lval;
 >           if (raw_buffer)
 >             memcpy (raw_buffer,
 >                     generic_find_dummy_frame (frame->pc, frame->frame) +
 >                     REGISTER_BYTE (regnum),
 >                     REGISTER_RAW_SIZE (regnum));
 >           return;
 >
 > Which will try to look up the pseudo in the buffer even if it isn't 
there.


Reveals a problem with the patch:
http://sources.redhat.com/ml/gdb-patches/2002-05/msg00416.html

For the moment a custom get_saved_register will get around this.


Andrew