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

David Fernandez david.fernandez.work@googlemail.com
Tue Dec 18 17:19:00 GMT 2012 
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
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