Re: [PATCH ARM]: Architectural Extensions (Matthew Gretton-Dann or Richard Earnshaw)

[Richard Earnshaw <rearnsha at arm dot com>]

On 18/12/12 17:19, David Fernandez wrote:
> On Tue, Dec 18, 2012 at 4:08 PM, Richard Earnshaw <rearnsha@arm.com> wrote:
> > On 18/12/12 15:30, David Fernandez wrote:
> > > Hi Richard,
> > >
> > > Great, thanks for the info. That will keep me going. I'll look into
> > > .inst, as I was using just a .word to define it for now.
> > >
> > > Just as a comment to the whole thing, AFAIK both Cortex-Rn and
> > > Cortex-An have in essence the same architecture, i.e. same instruction
> > > set, same possible extensions, etc. The difference is that while
> > > extensions like virt and sec are standard in Cortex-An, they are
> > > optional in Cortex-Rn.
> > >
> > > So I would suggest, that both armv7-r and arm-v7a should have access
> > > to the same extensions, just that armv7-r will have most disabled by
> > > default, while armv7-a would have some enabled by default.
> > >
> > > Also, the banked registers instructions are not part of any extension,
> > > and should be present all time. It is a bit weird that you don't have
> > > them unless you enable the virt extension.
> >
> > I'm not sure I understand what else you think is missing.
> >
> > The file
> >
> >          .arch armv7-r
> >          .thumb
> >          .syntax unified
> >          srsia   sp!, #4
> >          rfefd   sp!
> >
> > assembles without error for me.
> >
> > Perhaps you can provide a test-case.
> >
> > R.
>
> Something like:
>
>                  .arch   armv7-r
>                  .syntax unified
>                  .thumb
>                  mrs     r0, sp_usr
>                  bx      lr
>
> Complains, saying that this architecture does not support banked registers.
>
> I have to use .arch armv7-a and .arch_extension virt to make it work,
> but it should work in armv7-r and without the need for virtualization
> extensions.
>
> R

I'll look into it.  However, Rev C of the v7 ARM ARM is quite explicit 
in saying that this instruction is only available with the 
virtualization extension, so on that basis, I think GAS is right.  Do 
you have some document that appears to contradict this?

R.