Re: mcore registers

[Andrew Cagney <ac131313@redhat.com>]

> I have written a gdb stub for mcore-elf, and in my efforts to improve it I have noticed that gdb defines too many control registers for the mcore chip.  Despite having a 5-bit field in the control register move instructions, there are not actually 32 control registers on the mcore.  All the existing mcore designs, either current or planned, have only 13 control registers.  The gdb source code defines all 32, but  cr13..cr31 don't actually exist.
> 
> It speeds up the stub not to have to report the status of these phantom registers over the serial line.  Patching them out of gdb also allows the stub to keep its RAM requirement below 1K.
> 
> My question is, would it be advisable to make this change to the gdb mainline?  I realize that there will always be unintended consequences of such a patch.  Any thoughts?

Can you post the output from "maint print registers"?  If these 
registers are last, the stub can send back a short register packet (such 
a packet implies that remaining registers are zero, gdb shouldn't send a 
longer packet back to the stub).  It may also be possible to run length 
encode (phrase?) the "x" indicating that the the missing registers are 
not available.

If GDB, without other changes, dropped those registers, compatibility 
with existing stubs would be broken.

Andrew