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Re: [rfc][4/13] Eliminate read_register: read_register in deprecated_mips_set_processor_regs_hack
On Tue, Jun 12, 2007 at 03:49:57PM +0100, Maciej W. Rozycki wrote:
> Worse yet -- the approach that we have taken is generic. We can handle
> arbitrary MIPS32/MIPS64 processors as conforming to the current revisions
> of the base architecture specs and the application-specific extensions
> (ASEs) by decoding feature bits defined in cp0 config registers -- there
> four config registers defined so far; additional registers may need to be
> read for variable length register subsets (e.g. watch and performance
> counter registers).
I see - that sounds pretty nice; we just need to come up with a way to
support it in the rest of GDB. Perhaps we should simply bite the
bullet and have a late target description hook in addition to the
early one. We can't do without the early one; I added it e.g. for
existing MIPS remote targets, where the stub might send back 32-bit or
64-bit registers.
Or maybe I'm barking up the wrong tree entirely and we need more than
just a target description. The description could report which
registers are available and how big they are, and then GDB could
gather other details from the config registers.
> > I don't have an easy answer for this. Simplest would be to keep it
> > local to remote-mips.c (as it currently is), but change how it works;
> > move it from common_open to a new remote_mips_read_description, fetch
> > the PRID without going through GDB's register cache at all, and then
> > create an appropriate target description which specifies the processor
> > based on the PRID. It would be nicer if we could make it work for
> > remote.c too though.
>
> Well, it's actually in mips-tdep.c, so it should work for any MIPS
> target.
Have you moved the call? Right now, that function is only reached
through remote-mips.c.
> I guess this is unfeasible -- there are too many possibilites which are
> neither fixed nor easy to predict as you can see from the above. Unless
> the XML tags provide means for subsetting the architecture. Please note
> that to make the matter more exciting the subsets do overlap.
The XML tags provide whatever you want them to - it's very easy to add
new ones :-) We could provide the values of the config registers
directly in a description, for instance, and let mips-tdep.c interpret
them there. But it might be better to have GDB query them using
normal register methods.
--
Daniel Jacobowitz
CodeSourcery