Date   : Tue, 01 Mar 1988 20:33:46 CST
From   : mknox@emx.utexas.edu (Margaret H. Knox)
Subject: 22PUBLIC bug

Many people have by now either replaced their old DRI CCP completely,
or are using one of the PUBLIC patches which declare individual files
public.  Being lazy, I have been using the 22PUBLIC.ASM patch on
SIMTEL (from 1981) to make all .COM files on USER 0 accessible from
any other disk/user#.  

Over the years I have occasionally noticed that "certain" programs
would NOT always run correctly from other user numbers.  In particular,
MODEM7 would not run from any user number other than 0, although I
could set USER to 0, launch MODEM7, exit, set the USER to whatever
I wanted, and re-launch MODEM7 correctly.  Since this only affected
about 3 programs that I use with any frequency, and since it was
only a minor annoyance in the great antipathy of life, I mostly
ignored the problem.  

It didn't go away!!  (:-}      Late last night I got frustrated
enough to wonder why.

The problem is actually rather simple.  22PUBLIC traps "File Not
Found" returns when the CCP attempts to open a file for loading.
It then tries the same user number on disk A:, and then user 0
on disk A:.  If the file is not found after all that you get the
usual "?" error msg.  If the file *IS* found, however, it resets
the user number (so the running program will be in the correct
area) and re-enters the CCP load routine to finish loading the
now-open file.

The bug is that, if the file is greater than 16k (one extent)
the BDOS looks for the next extent in the WRONG user area!
The fix is simple -- just save the original user area, and
defer resetting the user area until after the load is completed.
The "patch" is more complicated -- there is not enough room
in the usual CCP patch locations.  I re-assembled CCP (from
an old disassembly) and that gave me enough room to restore
the user number in both the "command/load error" and "success"
routines.

Thought someone else might be interested.