Determining an ARM CPU's architecture

[Tixy]

On Mon, 2011-07-04 at 16:10 -0400, Nicolas Pitre wrote:
> On Mon, 4 Jul 2011, Tixy wrote:
> 
> > On Mon, 2011-07-04 at 15:45 -0400, Nicolas Pitre wrote:
> > > On Mon, 4 Jul 2011, Tixy wrote:
> > > 
> > > > We've been talking about data-processing instructions but I've also done
> > > > similar for "ldr pc, [...]" as Arnd suggested that we might have single
> > > > kernel binaries that execute on both ARMv4 and v5 hardware.
> > > 
> > > Sure, and I think we already do with some configurations.  But in that 
> > > case nothing should ever use Thumb mode in the kernel.

Nicolas, I thought you meant by this that for the ldr pc,[...] case we
didn't have to worry about interworking. I.e. don't code for the
possibility.

> > 
> > Should an ARMv7 kernel have code running in Thumb mode if it wasn't
> > configured with CONFIG_THUMB2_KERNEL?
> 
> I would say no.

If I was right about your meaning for the ARMv4/v5 statement, then
doesn't the same hold true for ARMv7 with no CONFIG_THUMB2_KERNEL? I.e.
don't worry about interworking? Where "don't worry" means either

a) ignore bit 0 of PC or
b) OOPs if bit 0 is set

rather than

c) switch to Thumb mode if the real instruction would have done that on
the current hardware

I like the idea of b) and throw away my code which checks interworking
behaviour of instructions.

-- 
Tixy