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Re: [patch 2/2] Implement gdbarch hook user_register_name on ARM
- From: "Ulrich Weigand" <uweigand at de dot ibm dot com>
- To: rearnsha at arm dot com (Richard Earnshaw)
- Cc: yao at codesourcery dot com (Yao Qi), gdb-patches at sourceware dot org
- Date: Wed, 22 Dec 2010 23:05:48 +0100 (CET)
- Subject: Re: [patch 2/2] Implement gdbarch hook user_register_name on ARM
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