== Proposal for a virtual memory layout for SDI ==

0x00000000 - 0x01ffffff	- 32m
invalid range: segfault when accessed. catches number-as-pointer bugs

0x02000000 - 0x0200ffff	- 64k
KIP page - mapped by kernel (usual is only 4096 bytes)

0x02010000 - 0x0202ffff	- 128k
UTCB area - zero-filled anonymous mem
hold up to 256 UTCB blocks (each 512 bytes)

0x02030000 - 0x08408000	- ~100m
invalid range: separation?

0x08408000 - <prog-end> - variable
.text segment loaded by elfexec

<prog-end> - <heap-end>	- variable
heap area - heap-end can be adjusted by brk() 
zero-filled anonymous mem on access

<head-end> - 0x90000000	- variable
invalid range: segfault. use brk to increase heap.

0x90000000 - 0x9fffffff	- 256m
user area for incoming mappings - used as fpage receive window

0xa0000000 - 0xb7ffffff - 384m
pager managed: mappings for shared / grant / special pages come in here

0xb8000000 - 0xbfffffff	- 128m
stack(s). initial thread's stack begins at 0xbff7ffff and the elfexec puts
the environment and program arguments on the initial stack.
further user threads determine themselves where to start
every page can be accessed and is filled with zero-initialized anonymous mem

0xc0000000 - 0xffffffff	- 1g
kernel memory - segfault on access