Category : Alternate Operating Systems - Quarterdeck DesqView, CP/M, etc
Archive   : QEMMPATS.ZIP
Filename : REALLOC.PAT

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.


---------------------------------------------------


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 with QEMM 5.00.


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

This patch is for:

QEMM-386 5.00

A separate procedure for other versions appears
earlier 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 QEMM.SYS file by
issuing the DOS command:

DIR QEMM.SYS

If the date on the file is

5:00 am

then this patch is the one to use. If there is no
QEMM.SYS file in this directory, then you probably
have a later version of QEMM-386; go back to the
section that deals with the patch for QEMM-386 5.1.

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

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

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

(If your QEMM.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\QEMM.SYS

(If your QEMM.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 7 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 the 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\QEMM.SYS C:\QEMM\QEMM.OLD

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

Hit the Enter key. COMP should return:


C:QEMM.SYS and C:QEMM.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 may vary, 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
QEMM.SYS and 75 in QEMM.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\QEMM.OLD C:\QEMM\QEMM.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 system fails after you perform this patch,
you can follow the instructions in the
"Installation" section of your QEMM-386 manual to
recover without resorting to a boot floppy. After
your system is booted successfully, copy the backup
of QEMM-386 that you made back to its original
name. If you are using QEMM-386 5.00, use the
following DOS command:

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

If you have QEMM-386 5.1, use the following DOS
command instead:

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

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

You may then wish to try the above procedure
again, in case a mistake was made.

* * * E N D O F F I L E * * *