Re: [patch 2/2] Implement gdbarch hook user_register_name on ARM

Ulrich Weigand
2010-12-22T22:05:59Z

Richard Earnshaw wrote:
> Overall, I think it's just best if 'fp' is treated like any other
> standard register alias on ARM and therefore that it always refers to
> R11. If we really want a register alias that refers to the *current*
> frame pointer register, then we need a new name that doesn't conflict
> with anything in the current or previous ABIs. Maybe a
> slightly-long-winded name like 'frame'?

Well, the problem is that that "fp" itself has a fixed meaning in GDB.

This shows up most problematically in the MI interface. When the MI
user interface application wants to select a frame in certain MI
commands, that frame has to identified via its "frame base" value.

However, there is no defined way to *query* that value. Therefore,
my understanding is that the MI frontends typically query the value
of the standard "fp" register to retrieve this value. If an architecture
back-end now goes and redefines what "fp" stands for, this will break
this MI frontend convention ...

Bye,
Ulrich

--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
Ulrich.Weigand@de.ibm.com