[CDG5] Process Manager

[Elliot Nunn]

Like Max, I had a bit of a code-generation problem last night. Thought
I'd share it for your entertainment.

As a big part of getting a System build to work, I am recreating the
makefiles for the Process Manager. The Process Mgr has a very novel
runtime (it actually gets loaded from 'scod' resources by the Segment
Loader). With not many clues around about how to build it, I decided
that I should take a deep dive at this point and get it round-tripping.
System 7.1 seems to be a good fit.

For context, the build is currently producing about 1/2 to 2/3 of a
System file, albeit of dubious quality.

Here is the function in question.

	/* CheckUnitTableEntry.  See if the UNITTABLE entry that this driver would occupy
	 * is acceptable.  For now, just checks whether entry is already in use.
	 */
	OSErr
	CheckUnitTableEntry(short resourceID)
		{
		register DCtlPtr	dCtlPtr;
		DCtlHandle			dCtlHdl;
		OSErr				result;

		result = noErr;
		dCtlHdl = (DCtlHandle) UNITTABLE[resourceID];
		if ( (dCtlHdl != nil) && ((dCtlPtr = *dCtlHdl) != nil) && ((dCtlPtr->dCtlFlags & DOpened) != 0) )
			result = portInUse;
			
		return(result);
		}

UNITTABLE is defined as (*(Handle **)(0x11C))

The unit table access was compiling to "EXT.L D0; MOVE.L $11C,A0; MOVE.L
$0(A0,D0.L*4),A3" when I wanted "EXT.L D0; MOVE.L $11C,A0; ASL #2,D0;
MOVE.L $0(A0,D0.L),A3". I fought with this until 1 am, changing headers,
types and compiler versions to no avail. I found that the same motif
appears in two or three places in that segment, and the ASL persists up
to System 7.1.2, after which it was refactored out of existence.

This morning I was about to email the list for help, when in a testament
to the "starting really hard at a problem" methodology, the answer came
to me. "MOVE.L $0(A0,D0.L*4),A3" is a very fancy-looking addressing
mode, I thought. It wouldn't work on a vanilla M68k... Oh! System 7.1
*does* run on a 68000, because it supports the Plus and Classic. (I
should know, because I grew up using it on a Classic.) The C compiler
was being run with the -mc68020 argument because I copied the makefile
from the ROM build. Now fixed!