thumb2 support

[Ian Lance Taylor]

On Wed, Oct 10, 2012 at 4:42 AM, Grant <emailgrant@gmail.com> wrote:
> Hello, I'm working with the BeagleBone and gcc-4.5.4 on Gentoo.  If I
> try to compile the 3.6 kernel with CONFIG_THUMB2_KERNEL, I get:
>
> arch/arm/boot/compressed/head.S:127: Error: selected processor does
> not support requested special purpose register -- `mrs r2,cpsr'
> arch/arm/boot/compressed/head.S:134: Error: selected processor does
> not support requested special purpose register -- `mrs r2,cpsr'
> arch/arm/boot/compressed/head.S:136: Error: selected processor does
> not support requested special purpose register -- `msr cpsr_c,r2'
>
> This post indicates that mainline gcc does not currently support thumb2:
>
> https://groups.google.com/d/msg/beagleboard/P52fgMDzp8A/vupzuh71vdYJ
>
> However, this indicates that thumb2 has been supported since 4.3:
>
> http://gcc.gnu.org/gcc-4.3/changes.html
>
> Can anyone clear this up?

The errors are coming from an assembler file that is not part of the
GCC sources.  Are those instructions valid for Thumb2?  I don't know.
If they are valid, then the issue is with the assembler, which is not
part of GCC; check the version of the GNU binutils that you have
installed.  If those instructions are not valid, then you need to
change your source.

Ian