[hppa-linux] Gateway instructions

[Alan Cox]

> Here's how I think it works:
> The GATE completer takes its privilege from the TLB entry for the page
> _containing_ the BRANCH-with-GATE (see 4-5 in the PARISC 2.0 book).  So
> what we do is have a page (at 0xC0000000, probably) that has
> appropriately high privilege level in the TLB, and yet is executable by
> the user-space process.  I think that means that the TLB access rights
> field is [100,11,11]:

Oh man its a vax  8)

Yeah that would be fairly believable. VMS actually does this sort of stuff
with the vax architecture equivalent for libraries - think  setuid mmap 8)