shared libraries on Pyramid 9820 OSx4.1

[Charles Hedrick]

As far as we can tell, OSx 4.1 is SVr2.  However it adds those SVr3
extensions that are likely to affect the ability to import application
code.  A full SVr3 port is quite an undertaking, and apparently they
haven't had time to get it finished.  OSx 4.1 is a compromise,
intended to provide maximum compatibility at the application level,
but to omit the things that are hairy to implement.  

In particular, shared libraries require a major reorganization of the
virtual memory subsystem.  One of the recent Usenix proceedings has
papers from a number of vendors describing the rewriting that a number
of them are doing in order to give their virtual memory subsystems the
ability to handle things such as shared libraries and copy-on-write.
It's non-trivial.  Many vendors will not find it practical simply to
adopt SVr3's implementation.