One other high-level comment: It would be nice to see the
arch-independent and x86 portions broken out and explained in their own
right, even if they're small patches. It's a bit cruel to make us
scroll through a thousand lines of sparc code to see the bits
interesting to us.
It would also be really nice to see a high-level breakdown explaining
what you had to modify, especially since this affects all of the system
calls that take a PROT_* argument. The sample code is nice, but it's no
substitute for writing it down.