Re: thumb2 support

[Rich Felker <dalias@libc.org>]

On Sun, May 04, 2014 at 12:54:40PM +0100, Justin Cormack wrote:
> On Wed, Apr 30, 2014 at 8:03 PM, Rich Felker <dalias@libc.org> wrote:
> > On Tue, Apr 29, 2014 at 06:09:14PM +0200, Wermut wrote:
> >> Hi
> >>
> >> I have tested the patch from Stephen Thomas at least for gcc 4.6, 4.7
> >> and 4.8. Seems to work. Would be nice if the 1.1.1 release will
> >> include a fix.
> >
> > It only works for armv7. On armv6k, I'm getting errors that the
> > instructions aren't supported. I think we could simply add !thumb as a
> > condition for the whole block...
> 
> The patch has the wrong conditional in, there are no standard
> __thumb__ and __thumb2__ defines, it is __ARM_ARCH_ISA_THUMB being 1
> or 2 that differentiates. armv6k does not support thumb2. I should
> have enough machines of different flavours to make a working patch.

I don't see __ARM_ARCH_ISA_THUMB getting defined at all (gcc 4.7.1) so
it doesn't seem reliable. __THUMBEL__ is defined in thumb mode
(presumably the EL is for little endian?) but that's the only thing
I'm getting that seems relevant other than __thumb__.

> We should be able to support just using thumb2, for thumb 1 I guess we
> can support a mixed mode with some files like this compiled for arm
> only, but the rest compiled with thumb, with interop turned on. Not
> sure how messy this will turn out to be.

armv6 does not seem to have thumb2, does it? And for armv7 I think it
should be reasonable to assume any thumb support is thumb2. Is this
wrong? Aside from the question of the macro name, I think the current
patch covers all cases that can be covered. (BTW as far as I can tell
there's no good reason to ever compile with -mthumb for pre-v7, but it
doesn't hurt to support it. All the asm is arm mode anyway, so -mthumb
doesn't get you the ability to run on obscure hardware that's
thumb-only unless you rewrite all the asm too.)

Rich