Quarterdeck Technical Note

Subject: Patching QEMM-386 5.00, 5.10, 5.11, and 5.12 to resolve
problems with programs that resize EMS or XMS handles

Background: Starting with QEMM-386 5.00, QEMM-386 supports both the EMS
(Expanded Memory Specification), which governs access to expanded
memory, and the more recent XMS (Extended Memory Specification), which
governs access to extended memory. Requests for EMS and for XMS memory
are both filled from the same pool of QEMM-managed memory, and EMS and
XMS handles (numbers that the memory manager returns to a program when
the program takes a chunk of memory, so that the program can quickly
identify the chunk when it next communicates with the memory manager)
are managed together by QEMM-386.

Both EMS and XMS contain a call that programs can make to reallocate
blocks of memory; that is, to take a handle that the program has already
received and increase or decrease the chunk of memory to which the
handle refers. Users of QEMM-386 versions 5.00 through 5.12 may
experience system instability under certain circumstances when a program
makes an EMS or XMS call to increase the size of a handle. The symptom
is likely to be a system crash or a reboot.

Users of versions of QEMM-386 after version 5.12 should not experience
this problem. In the meantime, QEMM-386 can be patched to eliminate the
problem.


The following procedure is intended to prevent system crashes and
reboots when Reallocate Memory EMS and XMS functions are used to
increase the size of EMS and XMS handles. This procedure is for use
with QEMM-386 versions:

5.10
5.11
5.12

***************************************************

Do NOT use this patch for QEMM-386 5.0; a separate procedure for
QEMM-386 5.0 is later in this technote. If you are in doubt, go to the
directory where the QEMM-386 files are located and check the date on the
QEMM386.SYS file by issuing the DOS command:

DIR QEMM386.SYS

If the date on the file is

5:10 am
5:11 am
5:12 am

then use the patch in this section. If there is no QEMM386.SYS file in
this directory, then you probably have an earlier version of QEMM-386;
go forward to the section that deals with the patch for QEMM-386 5.0.

***************************************************

1) Make a copy of the QEMM386.SYS file in your QEMM directory. We are
about to alter your current copy of QEMM386.SYS; the copy you make will
serve as a backup in case this operation fails.

COPY C:\QEMM\QEMM386.SYS C:\QEMM\QEMM386.OLD

(If your QEMM386.SYS is not located in the QEMM directory of the C:
drive, change the path accordingly.)

2) Go to the DOS directory on the hard disk and type:

DEBUG C:\QEMM\QEMM386.SYS

(If your QEMM386.SYS is not located in the QEMM directory of the C:
drive, change the path accordingly.)

Hit the Enter key; you should see the DEBUG prompt, which is a hyphen.

3) At the DEBUG prompt, type:

S 100 L F000 75 6 1 0E

Hit the Enter key; DEBUG should return a segment address and an offset:

xxxx:yyyy

4) At the DEBUG prompt again, use the segment address and offset that
was just returned to give the DEBUG command:

E xxxx:yyyy EB

The address that DEBUG returned in step 3 should be used in place of the
address xxxx:yyyy, which we use as an example. Hit the Enter key; the
DEBUG prompt should return in a moment.


5) At the DEBUG prompt, type

W

Hit the Enter key; DEBUG will announce that it is writing a certain
number of bytes, then it will return the DEBUG prompt.

6) At the DEBUG prompt, type

Q

Hit the Enter key to exit DEBUG and return to DOS.

7) To double-check your patch, type the following from the DOS prompt in
your DOS directory:

COMP C:\QEMM\QEMM386.SYS C:\QEMM\QEMM386.OLD

(If your QEMM386.SYS is not located in the QEMM directory of the C:
drive, change the path accordingly.)

Hit the Enter key. COMP should return:


C:QEMM386.SYS and C:QEMM386.OLD

Compare error at OFFSET xxxx File 1 = EB

File 2 = 75

Eof mark not found

Compare more files (Y/N)?

The value xxxx after OFFSET will vary from version to version of QEMM
5.1, but the rest of the message should be the same: it tells us that
there is exactly one byte difference between the files, and the
differing byte is EB in QEMM386.SYS and 75 in QEMM386.OLD. If COMP
returns the message:

Files compare ok

...then you probably failed to use DEBUG's W command to save your
change, or you have compared the wrong files. If COMP returns more than
one compare error, or if the bytes returned by the compare error don't
match those in the above example, the procedure has failed. In this
case, use the DOS command:

COPY C:\QEMM\QEMM386.OLD C:\QEMM\QEMM386.SYS

... to restore the original file, and try again.

If the patch was successful, you should now reboot the system and test
the patched version of QEMM- 386. If the patched version of QEMM-386
fails, see the section at the end of the technote on restoring your
original copy. Otherwise, you are finished with the patch.
---------------------------------------------------


Note:

The above patch *must* be applied to STANDARD MODE Win 3.00a users.