[hppa-linux] memory layout

[Alan Cox]

> Talking about only pa1.1 or 32 bit CPUs, I would say the same layout
> can be used as Linux on Intel does. That is kernel mapped at 0xc0000000.
> So 3 Gig for User space and 1 Gig for kernel. Of course, other ppl may
> have different ideas. 

If you want to run PH/UX binaries then you need to probably follow their
layout

> PA has this strange concept of Spaces and they have those 
> space registers %sr0 to %sr7. This reminds me of Intel's segment 
> registers. And whoever wanted to do any serious OS like Unix on 80386
> never liked segments.

Spaces is more segments done right. The reason we dont use segmentation
to split user/kernel on x86 any more is simply performance - it costs us
1 clock per dword copied to/from luser space.

The m68k people use the 'spaces' equivalent on the m68k quite heavily