Updating the minimum armv6 requirement

[Ian Lepore]

On Tue, 2014-03-11 at 13:19 +1300, Andrew Turner wrote:
> I've been looking at code that uses 64-bit C++ atomic operations on
> armv6. These require the ldrexd and strexd instructions that are
> present on armv6k.
> 
> The problem is there is a mismatch between clang and binutils. Clang
> thinks armv6k is an arm1136jf-s and sets the cpu in the asm output as
> one. Binutils will see the cpu and think clang means an earlier armv6
> instruction set that lacks the above instructions.
> 
> In this case both are correct as prior to the r1p0 release of the
> arm1136jf-s core it was an armv6 core, and as of the r1p0 release it
> became an armv6k core.
> 
> All of this is uninteresting for FreeBSD as the only ARMv6 SoC we run
> on appears to be the bcm2835, and maybe some Marvell parts. As the
> bcm2835 is an arm1176jzf-s and we are unlikely to get a new ARMv6 port I
> am suggesting we make this the minimum requirement. It appears NetBSD
> has the same requirement as clang will set the cpu to arm1176jzf-s when
> building for NetBSD and armv6.
> 
> My proposal is to have the same CPU requirement as NetBSD for armv6. Is
> anyone working on an SoC that would be affected by this?
> 
> Andrew

I think this is fine.  I thought we already had a rule that armv6k was
the minimum.  If we just need the compiler to emit a different .cpu
directive to keep the assembler happy, that should be fine.  Since we
don't support the pre-'k' variants of armv6, there should be no
conflicts.

-- Ia