Shared system routines

[tbray at mprvaxa]

Shared system routines were a primary design objective of VMS, and several
different tools are provided for building and using them.  However, the 
goal was not easily achieved, and even now, 5 years later, there were some
pretty fundamental changes made to the linker (read loader) with VMS version
3, to eliminate some obscure contradictions that had been introduced.

People in the group are correct when they predict horrible problems arising
in making the loader smart enough to correctly all the permutations and
combinations this can introduce.  And with real memory getting so cheap, I
wonder if it's worth it. 

The way it's done at VMS run-time is that the shared stuff can appear anywhere
in the address space, with the corresponding entries in the page table 
containing a flag indicating a shared reference. The code is then found
via ANOTHER page table (called a global section table). This is referred to
as a 'global valid page fault'.  

             thinking that the new Amdahls support 64M phys memory (!!!!!!!),
					...microsoft!ubc-visi!mprvaxa!tbray