Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.soft-sys.andrew
Subject: Re:  porting atk to VMS ?
Message-ID: <4283@auspex.auspex.com>
Date: 8 Nov 90 18:44:52 GMT
References: <9011071749.AA03496@riposte>
Organization: Auspex Systems, Santa Clara
Lines: 62


 >The dynamic loading is probably not the hard part of porting
 >to VMS. VMS actually has a callable dynamic loader, in the form
 >of the 'lib_$find_symbol' library call. This call takes an object file
 >name and a symbol name. It loads the object file and returns a pointer
 >to the given symbol (if present).  For an example of layer ATK on top
 >of an existing dynamic loader look at the Apollo specific code, which
 >uses the existing Apollo/Domain-OS dynamic loader.

Or the IBM RISC System/6000 dynamic loader, which uses the existing AIX
3.1 dynamic loader.

Bear in mind, though, that both those schemes depend on the ability to
mark a particular symbol in the dynamically loaded file as
"distinguished" by making it the "entry point symbol"; I don't know if
the VMS dynamic loader has this facility, but the SunOS 4.1/System V
Release 4 dynamic loader does *not*, as far as I know, so you may have
to look up that symbol explicitly.  The way that seemed to work in my
cobbled-up prototype for SunOS 4.1/S5R4 is to do:

	/*
	 * Construct name of GetClassInfo symbol from the package name
	 * by stripping off the suffix and appending "__GetClassInfo".
	 * You can't get the entry point value from a shareable object
	 * from the "dl*()" routines, which is why we have to do this
	 * stuff.
	 * We strip off the suffix because "doindex", curse its soul,
	 * hands us the last component of the name of the *file* as
	 * the package name, suffix and all.
	 */
	(void) strcpy(epname, name);
	p = strrchr(epname, '.');
	if (p == NULL)
		p = epname + strlen(epname);
	(void) strcpy(p, "__GetClassInfo");

to construct the name of the symbol in question.  "name" is the second
argument to "doload".  The "path" (fifth) argument is the actual
pathname of the file to be loaded.

Note also that you will have to ensure that some symbols in the "class"
loader code are accessible to the dynamic loader, as the
dynamically-loaded object may refer to them (e.g.,
"class_RoutineStruct").  This appears to require varying amounts of
hackery on Domain/OS and AIX 3.1, and also requires hackery in SunOS
4.1/S5R4:

	in Domain/OS, "doload()" explicilty calls the loader to add them
	to the Known Global Table;

	in AIX 3.1, the "class" loader ".o" files are linked together
	into a single ".o" file and the linker is explicitly told to
	export them;

	in SunOS 4.1 and (probably) S5R4, the best or maybe even only
	way to do so is to make "libclass.a" into a *shared* library.

(No, the prototype doesn't really "work" - I hand-built pieces of it
instead of changing the Imakefiles, and I've only tested it with the
stuff in the "overhead/class/testing" directory, not with ATK itself. 
I've no idea when I'll do anything further on it, and there are some
unresolved issues waiting some responses to mail I sent out....)