unaligned exception load emulation bugs

[Adrian Chadd]

hi!

I've discovered that our unaligned exception load emulation path likely
hasn't worked in a while due to some exciting compiler behaviour.

https://reviews.freebsd.org/D25040

I'd appreciate some pointers/suggestions on better ways to fix this. As I
haven't unboxed my mips64 hardware in a while I'd also appreciate some
testing there too.

I think it's worth just combining the two macros and the address increment
into a single macro w/ address offset just to be (a) slightly more
efficient and (b) ensure that the dependency bits for assembler arguments
are done right, but I'd prefer to do that in a subsequent commit.

Thanks,


-adrian