Shareable Images/dynamic binding possible with Unix?

[Guy Harris]

>The same funcationality is avaiable in most implementations of unix.

Well, not exactly.  Various people have whipped up packages that sit
*atop* most implementations of UNIX to provide this, but most
implementations (implementations, not machines shipped with the
implementations) don't have it yet.  The ones that do, or will, include:

	SunOS 4.1 and later, and System V Release 4 (the latter has a
	mechanism basically the same as the former in its API);

	OSF/1;

	AIX 3.x;

	the NeXT version of Mach, I think;

	possibly other versions of Mach.

Previous releases of S5 from AT&T didn't have it (yes, S5R3 had shared
libraries, but *not* any built-in ability to link in stuff *during* the
execution of a program), and no current BSD releases have it, for
example.

>I've only used this under the current version of SunOS (4.1.1), but I've
>been told that it had problems in previous releases.

It had an *extremely* severe problem in releases prior to 4.1, which
rendered it completely unusable; the problem is called "nonexistence". 
It didn't show up until 4.1; there may have been some bugs in 4.1's
version that were fixed in 4.1.1 (there's one bug in 4.1's version that
*didn't* get fixed, alas, namely that the run-time loader can get
confused and think "/dev/zero" is still open from when it first loaded
the shared libraries for the program).