Saving to 32 bits of GPRs in signal context

[Segher Boessenkool]

> I think actually it would be useful to have the saving/restoring of
> the high 32 bits controlled by a prctl, so that programs have to ask
> explicitly for the new behaviour (and programs that don't want to use
> the high 32 bits don't incur the extra overhead).

This prctl() is needed if you want to support DSOs containing
64-bit insns.  It would be nice to have some ELF flag as well
though, so most of this can be handled automatically.


Segher