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Information about “OVL312”
OVL is a powerful overlay manager system for use with Microsoft LINK.
Overlays are portions of program code which are loaded from disk into
memory on an "as-needed" basis. Overlays allow a very large program to
use a relatively small amount of memory.
LINK.EXE, Microsoft's Overlay Linker, included with MS-DOS and Microsoft
languages, versions 3.x, 5.x, and some 2.x versions, allow creation of
overlaid programs. However, LINK only inserts software interrupts and
some overlay information in the program for an overlay manager to use.
LINK doesn't provide the actual code that loads the proper overlay from
disk and passes control to it. That's a job for an overlay manager, and
that's where the OVL overlay managers come in.
OVL "manages" overlays. OVL loads overlays from disk at the appropriate
time and jumps program execution to the overlay code. OVL managers have
been tested with MASM 4.0 and 5.0; Turbo C 1.0, 1.5 and 2.0; QuickBASIC
4.0 and 4.5; Microsoft's BASCOM 6.0; and Clipper (PRONK.EXE, an included
support utility, must be used with Clipper programs). Other languages
that compile to standard Microsoft Overlay LINKable object modules may
also work with OVL.
FILE1933.TXT
Disk No: 1933
Disk Title: OLV312
PC-SIG Version: S1
Program Title: OLV312
Author Version: 3.12
Author Registration: $80.00
Special Requirements: Other programming software and MicroSoft Link.
OVL is a powerful overlay manager system for use with Microsoft LINK.
Overlays are portions of program code which are loaded from disk into
memory on an ``as-needed'' basis. Overlays allow a very large program
to use a relatively small amount of memory.
LINK.EXE, Microsoft's Overlay Linker, included with MS-DOS and Microsoft
languages, versions 3.x, 5.x, and some 2.x versions, allow creation of
overlaid programs. However, LINK only inserts software interrupts and
some overlay information in the program for an overlay manager to use.
LINK doesn't provide the actual code that loads the proper overlay from
disk and passes control to it. That's a job for an overlay manager, and
that's where the OVL overlay managers come in.
OVL "manages" overlays. OVL loads overlays from disk at the appropriate
time and jumps program execution to the overlay code. OVL managers been
tested with MASM 4.0 and 5.0; Turbo C 1.0, 1.5 and 2.0; QuickBASIC 4.0
and 4.5; Microsoft's BASCOM 6.0; and Clipper (PRONK.EXE, an included
support utility, must be used with Clipper programs). Other languages
that compile to standard Microsoft Overlay LINKable object modules MAY
also work with OVL.
PC-SIG
1030D East Duane Avenue
Sunnyvale Ca. 94086
(408) 730-9291
(c) Copyright 1989 PC-SIG, Inc.
GO.TXT
╔═════════════════════════════════════════════════════════════════════════╗
║ <<<< Disk #1933 OVL312 >>>> ║
╠═════════════════════════════════════════════════════════════════════════╣
║ Use PKXARC to extract files onto your hard drive. ║
║ ║
║ To print documentation, type: COPY OVL.DOC PRN ║
╚═════════════════════════════════════════════════════════════════════════╝
BNEST1.BAS
sub nest1(i) static
print:print"in nest1";i;
for j=0 to 1
call nest2(j)
next j
end sub
BNEST2.BAS
sub nest2(i) static
print:print"in nest2";i;
for j=0 to 1
call nest3(j)
next j
end sub
BNEST3.BAS
sub nest3(i) static
print:print"in nest3";i;
for j=0 to 1
call nest4(j)
next j
end sub
BNEST4.BAS
common shared b
sub nest4(i) static
print:print"in nest4";i;
print:print "Value of b variable is "b;
b=b+1
end sub
DOGGEREL.TXT
***************************************************************************
* *
* Ringo is a moronic dog, *
* has the braincase of a frog. *
* He's so stupid that you see, *
* has the IQ of a flea. *
* *
***************************************************************************
MASMTEST.ASM
;DOSSEG
.MODEL large
.STACK 100h
PUBLIC ov1message,ov2message,ov3message,mainproc
EXTRN ov1:PROC,ov2:PROC,ov3:PROC
.CODE
start:
mov ax,dgroup
mov ds,ax
mov dx,offset message
mov ah,9
int 21h
call ov1
call ov2
call ov3
mov ax,4c00h
int 21h
mainproc PROC
mov dx,offset mainmessage
mov ah,9
int 21h
ret
mainproc ENDP
.DATA
message db 13,10,"Hello from Masmtest.",13,10,'$'
ov1message db 13,10,"Hello from Overlay 1.",13,10,'$'
ov2message db 13,10,"Hello from Overlay 2.",13,10,'$'
ov3message db 13,10,"Hello from Overlay 3.",13,10,'$'
mainmessage db 13,10,"Hello from Mainproc.",13,10,'$'
END start
MULTA.ASM
.MODEL large
.DATA
EXTRN messa:FAR
.CODE
PUBLIC multa
multa PROC
call far ptr temp
ret
db 20000 dup (?)
multa ENDP
temp proc
jmp far ptr temp2
db 20000 dup (?)
temp2:
mov ax,SEG messa
mov ds,ax
mov dx,offset messa
mov ah,9
int 21h
ret
temp endp
END
MULTB.ASM
.MODEL large
.DATA
EXTRN messb:FAR
.CODE
PUBLIC multb
multb PROC
call far ptr temp
ret
db 20000 dup (?)
multb ENDP
temp proc
jmp far ptr temp2
db 20000 dup (?)
temp2:
mov ax,dgroup
mov ds,ax
mov dx,offset messb
mov ah,9
int 21h
ret
temp endp
END
MULTC.ASM
.MODEL large
.DATA
EXTRN messc:FAR
.CODE
PUBLIC multc
multc PROC
call far ptr temp
ret
db 20000 dup (?)
multc ENDP
temp proc
jmp far ptr temp2
db 20000 dup (?)
temp2:
mov ax,_data
mov ds,ax
mov dx,offset messc
mov ah,9
int 21h
ret
temp endp
END
MULTD.ASM
.MODEL large
.DATA
EXTRN messd:FAR
.CODE
PUBLIC multd
multd PROC
call far ptr temp
ret
db 20000 dup (?)
multd ENDP
temp proc
jmp far ptr temp2
db 20000 dup (?)
temp2:
mov ax,dgroup
mov ds,ax
mov dx,offset messd
mov ah,9
int 21h
ret
temp endp
END
MULTEST.ASM
DOSSEG
.MODEL large
.STACK 100h
PUBLIC messa,messb,messc,messd
EXTRN multa:PROC,multb:PROC,multc:PROC,multd:PROC
.CODE
start:
mov ax,dgroup
mov ds,ax
mov dx,offset message
mov ah,9
int 21h
mov ah,1 ; keyboard input with echo
int 21h
and al,0dfh ; upshift lowercase chars
cmp al,65 ; 'A' keypress
jne nota
call multa
jmp short start
nota:
cmp al,66 ; 'B' keypress
jne notb
call multb
jmp short start
notb:
cmp al,67 ; 'C' keypress
jne notc
call multc
jmp short start
notc:
cmp al,68 ; 'D' keypress
jne notd
call multd
jmp short start
notd:
cmp al,81 ; 'Q'
jne start ; invalid keypress, reloop
mov ax,4c00h ; terminate with errorlevel 0
int 21h
.DATA
message db 13,10,"Press A,B,C,D or Q to quit: ",'$'
messa db 13,10,13,10,"Now in process A",13,10,'$'
messb db 13,10,13,10,"Now in process B",13,10,'$'
messc db 13,10,13,10,"Now in process C",13,10,'$'
messd db 13,10,13,10,"Now in process D",13,10,'$'
END start
OV1.ASM
.MODEL large
.DATA
EXTRN ov1message:FAR,mainproc:FAR
.CODE
PUBLIC ov1
ov1 PROC
mov dx,offset ov1message
mov ah,9
int 21h
call mainproc
ret
ov1 ENDP
END
OV2.ASM
.MODEL large
.DATA
EXTRN ov2message:FAR
.CODE
PUBLIC ov2
ov2 PROC
mov dx,offset ov2message
mov ah,9
int 21h
ret
ov2 ENDP
END
OV3.ASM
.MODEL large
.DATA
EXTRN ov3message:FAR
.CODE
PUBLIC ov3
ov3 PROC
mov dx,offset ov3message
mov ah,9
int 21h
ret
ov3 ENDP
END
OVL.DOC
======================
OVL 3.12 DOCUMENTATION
======================
LICENSE AND WARRANTY
--------------------
OVL copyright 1988, 1989 by Michael E. Devore. All rights
reserved.
The copyright holder licenses you to use, copy, and distribute
OVL files for yourself and others subject to the following four
restrictions:
1. The OVL package must be copied and distributed only in its
original, unmodified form. This includes the documentation,
executable, source, object, and all example files.
2. No fee or other compensation can be charged for copying or
distributing the program files. The only exceptions are
user groups and incorporated public domain or shareware
software distributors who may charge a handling fee for its
distribution NOT TO EXCEED $8.00 PER COPY. ONLY ONE COPY
PER COMPUTER DISK IS ALLOWED FOR SUCH DISTRIBUTION.
3. OVL files may NOT be distributed in combination with any
other products, software or hardware, without the express
written permission of Michael E. Devore.
4. OVL files are for your personal use only and may NOT be used
for commercial applications. See the PROVL program
description in this documentation file if you need to use a
version of the OVL overlay manager package commercially or
need a custom version of OVL.
There is no warranty of any kind with OVL and the copyright
holder is not liable for any damages of any kind whatsoever,
directly or indirectly, that may occur due to use of, or
inability to use, this software. By using or distributing OVL
you agree to these terms. If you do not agree to these terms,
you may not use or distribute OVL.
It is the copyright holder's intention to fix any errors in OVL
and to allow both its noncommercial use and distribution free of
charge. The copyright holder, however, is NOT LEGALLY OBLIGATED
TO DO SO.
This documentation copyright 1988,1989 by Michael E. Devore.
All rights reserved.
OVL files page 1 of 2
OVL FILES
---------
Included in the OVL package should be the following files:
OVL.DOC (OVL documentation file)
LINKOVL.OBJ (standard OVL overlay manager)
OVLSTONE.OBJ (modifiable OVL overlay manager)
MAPOVL.EXE (Overlay mapping utility, executable)
MAPOVL.C (Turbo C source code for the MAPOVL program)
SCULPT.EXE (Utility needed to use the OVLSTONE overlay
manager, executable)
SCULPT.C (Turbo C source code for the SCULPT program)
SPLIT.EXE (Separate overlay files utility, executable)
SPLIT.C (Turbo C source code for the SPLIT program)
PRONK.EXE (Utility to allow use of Clipper or indirect
calls to overlays with OVL)
MASMTEST.ASM (MASM compatible assembly language example files)
MASMTEST.OBJ
OV1.ASM
OV1.OBJ
OV2.ASM
OV2.OBJ
OV3.ASM
OV3.OBJ
COW.C (C example files)
FARM.C
HORSE.C
PIG.C
PIGLET.C
SHEEP.C
QBNEST.BAS (QuickBASIC 4.x and BASCOM 6.x example files)
BNEST1.BAS
BNEST2.BAS
BNEST3.BAS
BNEST4.BAS
PRTEST.ASM (MASM compatible assembly language example files
PRTEST.OBJ for PRONK demonstration)
PTEST2.ASM
PTEST2.OBJ
PTEST3.ASM
PTEST3.OBJ
OVL files page 2 of 2
MULTEST.ASM (MASM source code to multiple overlay area
MULTA.ASM demonstration program)
MULTB.ASM
MULTC.ASM
MULTD.ASM
MULTEST.EXE (Demonstration program to show use of multiple
overlay areas)
DOGGEREL.TXT (Alternate loading message example for SCULPT)
What is OVL? page 1 of 2
What is OVL?
------------
OVL is a powerful overlay manager system for use with Microsoft
LINK. So what is an overlay manager and what good is it? To
answer that question we first need a little background on what
overlays are and why they are useful.
Overlays are portions of program code which are loaded from disk
into memory on an as-needed basis.
Use of overlays allows an extremely large (potentially equal to
hard disk capacity) program to run in a much smaller amount of
memory. Code from the program's .EXE file is brought in from
disk (overlaid) only when the program needs it. Since all
overlays share the same memory space, the memory requirements
can be much less than the total code size of the program. Also,
there is no longer a need for the messy chaining, spawning, or
exec'ing to another program that some languages require.
There is a tradeoff for these advantages. The tradeoff is the
time and code overhead necessary to read overlays in from disk.
If you make the decision to use overlays with your program, any
timing critical code should not be divided between overlays.
For most applications, though, the relatively small amount of
time it takes to read in an overlay from disk is not important
if transfers to overlays are not overdone or poorly timed.
Constant shuttling between overlays is an exercise guaranteed to
give disappointing results. A little bit of thought will go a
long way towards efficient overlay operation.
LINK.EXE, Microsoft's Overlay Linker, included with MS-DOS and
Microsoft languages, versions 3.x, 5.x, and some 2.x versions,
allow creation of overlaid programs. However, LINK only inserts
software interrupts and some overlay information in the program
for an overlay manager to use. LINK doesn't provide the actual
code that loads the proper overlay from disk and passes control
to it. That's a job for an overlay manager, and that's where
the OVL overlay managers come in.
OVL "manages" overlays. OVL loads overlays from disk at the
appropriate time and jumps program execution to the overlay
code.
Beginning with version 2.2, OVL supports use of multiple overlay
areas. To see detailed examples of how to use this option and
why it is useful, read the section entitled 'USING MULTIPLE
OVERLAY AREAS (Advanced Operation)'.
What is OVL? page 2 of 2
Version 3.0 of OVL introduced a linkable version of OVL called
LINKOVL.OBJ in addition to the OVL.EXE standalone version.
Several options were added with version 3.0, including support
for a overlay log file for debugging purposes, support of
separate overlay files, and a couple of other options. Examples
and a description of these options are covered in the 'COMMAND
LINE OPTION //x (Advanced Operation)' and 'OTHER COMMAND LINE
OPTIONS (Advanced Operation) sections.
Version 3.12 of OVL eliminates the obsolete stand-alone version
of OVL previously available as OVL.EXE. In OVL.EXE's place
version 3.12 adds another linkable overlay manager, called
OVLSTONE.OBJ, that eliminates the use of runtime switches and
adds some unique enhancements of its own.
If you are or become completely overwhelmed at the size or
complexity of OVL, be sure to read the 'TOO LARGE! DOESN'T WORK
WITH MY DEBUGGER! TOO COMPLICATED! PROVL TOO EXPENSIVE!'
section for an alternative to the OVL overlay managers.
System requirements page 1 of 1
SYSTEM REQUIREMENTS
-------------------
The OVL package requires an IBM PC or PS/2 microcomputer or
close compatible with MS-DOS or PC-DOS operating system version
2.1 or later. A copy of Microsoft's Overlay Linker version 3.06
or later, or a version of Microsoft's Object Linker version 3.00
or later, or a version of Microsoft's Segment-Executable Linker
version 5.x, is needed to link together the object modules of
the overlaid program.
In their standard configurations LINKOVL.OBJ and OVLSTONE.OBJ
require 14K (kilobytes) RAM, in addition to the memory
requirements of the overlaid program. Use of multiple overlay
areas or increasing the relocation table buffer size with OVL's
/ZB option will increase memory requirements above the standard
configurations. The /ZBn option can also be used to reduce the
default memory requirement by 1K.
OVL specifications and requirements page 1 of 2
OVL SPECIFICATIONS AND REQUIREMENTS
-----------------------------------
NOTE: Throughout this documentation, when both the LINKOVL and
OVLSTONE overlay managers operate identically they will be
generically referred to as OVL.
* LINKOVL.OBJ and OVLSTONE.OBJ have been tested with MASM 4.0
and 5.0; Turbo C 1.0, 1.5 and 2.0; QuickBASIC 4.0 and 4.5;
Microsoft's BASCOM 6.0; and Clipper (PRONK.EXE, an included
support utility, must be used with Clipper programs). Other
languages that compile to standard Microsoft Overlay LINKable
object modules MAY also work with OVL.
* Use of OVL with QuickBASIC 4.x and BASCOM 6.0 requires
compiling the program with the /O option of BC.EXE.
* The object files created by versions of QuickBASIC earlier
than 4.0 abort with an error if a link is attempted with
overlays. Therefore, OVL will NOT work with versions of
QuickBASIC earlier than 4.0. This is a limitation of the
earlier versions of QuickBASIC and not an error or
shortcoming in OVL.
* The Microsoft LINK object module preprocessor utility
PRONK.EXE must be used if indirect calls to overlay code are
required. Otherwise, calls to a function or procedure FROM
the root code TO overlay code, or from one overlay to another
(INTERoverlay calls) MUST be direct, that is, not indirectly
through a pointer. This restriction is necessary because
Microsoft LINK can only set up an interrupt invoking the
overlay manager for direct calls to program code. For
assembly language programs this means that interoverlay calls
to procedures must be coded as CALL ADDR, not CALL MEM/REG.
For 'C', interoverlay function calls should be directly
called, not called through a pointer to a function. Calls
within an overlay (INTRAoverlay calls), within the root code,
or FROM an overlay TO the root can be made indirectly.
QuickBASIC and BASCOM programs should not be affected by this
restriction unless non-BASIC modules which use indirect calls
to overlays are also linked in. Clipper programmers must use
PRONK whenever they use the LINKOVL.OBJ overlay manager.
* Microsoft LINK requires the presence of at least one overlay
when linking LINKOVL.OBJ or OVLSTONE.OBJ with a program's
object modules. An attempt to link either overlay manager
with a program that doesn't have at least one overlay will
cause LINK to abort with several "Unresolved external"
errors.
* OVL has a limit of twelve overlays in a program. More than
twelve overlays will cause OVL to abort with a "Too many
overlays." error upon startup. PROVL, the enhanced version
of OVL, has a limit of 63 overlays -- LINK's current maximum.
LINKOVL specifications and requirements page 2 of 2
* OVL supports calls from one overlay to another (nesting).
Overlays can be nested up to four levels. An attempt to nest
deeper than four overlays will cause OVL to abort with an
"Overlays nested deeper than 4 levels." error. PROVL
supports a nesting depth of 32 levels.
* OVL requires use of the Microsoft LINK default overlay
interrupt 63 (3fh). Do not use the /OVERLAYINTERRUPT or /O
option of LINK to change the overlay manager interrupt.
PROVL supports changing the default overlay manager interrupt
via the /O option of LINK.
* OVL will work with the /EXEPACK or /E option of LINK, if the
program containing overlays is suitable for using the
/EXEPACK option. OVL will work with files packed using
Microsoft's EXEPACK.EXE utility as well.
* OVL supports two overlay areas: the overlay area allocated by
Microsoft LINK during the linking process and optionally one
other overlay area. If two overlay areas are used, memory
allocation for the second overlay area is made in normal DOS
memory. As a result, the amount of memory available to the
loaded program decreases. This decrease, that is, the amount
used by the second overlay area, is equal to the largest
overlay file that will load into that overlay area rounded up
to the next 512-byte block. PROVL supports up to nine
overlay areas.
* After your program has been linked with OVL, do NOT change
the program's name. OVL attempts to load overlays from the
executable file name assigned during the linking process. If
the file name has been changed, OVL will abort with a "File
not found." error when it tries to load an overlay. To
change the name of your program, you must relink the program
using the new name for your executable file in the link
syntax.
* LINKOVL uses the PATH environment variable when searching for
the overlaid program or file. If LINKOVL attempts to load an
overlay and the program containing that overlay is neither in
the current directory nor in a directory in the PATH
variable, LINKOVL will abort with a "File not found." error.
* OVLSTONE uses the environment variable specified by the
SCULPT.EXE utility when searching for the overlaid program or
file. If OVLSTONE attempts to load an overlay and the
program containing that overlay is neither in the current
directory nor in a directory listed in the SCULPT specified
environment variable, OVLSTONE will abort with a "File not
found." error.
* Both OVL overlay managers use a maximum of 24 bytes of the
overlaid program's stack during their operation.
Using LINKOVL.OBJ page 1 of 5
USING LINKOVL.OBJ (Basic Operation)
-----------------------------------
To demonstrate how to use LINK to set up overlays with
LINKOVL.OBJ three sample program modules have been included in
the OVL package. One set is written using MASM 5.0, another
using Turbo C, and the third using QuickBASIC 4.x.
As stated in the Microsoft LINK documentation, you MUST
compile using a large code model for for your programs to work
correctly with overlays. For MASM 5.0, this means you must
compile using .MODEL MEDIUM (far-code, near-data), .MODEL LARGE
(far-code, far-data), or .MODEL HUGE (far-code, far-data). If
you are using an earlier version of MASM you need to make sure
that PUBLIC procedures in overlays are declared FAR if they
called by the root code or another overlay. For Turbo C
versions 1.x and 2.0, compile your files using the medium,
large, or huge model. QuickBASIC and BASCOM users must compile
their program with BC.EXE using the /O option. Microsoft's
runtime program for BASIC, BRUNxx.EXE, will not work with the
OVL package. Clipper programmers should carefully read the
'USING PRONK.EXE' section before using OVL on their programs.
The first example will use the assembly language .ASM files
MASMTEST, OV1, OV2, and OV3, written using Microsoft's MASM 5.0.
Although the .MODEL LARGE is used for these example files,
.MODEL MEDIUM and .MODEL HUGE should work in exactly the same
fashion for overlaying purposes. Since MASM requires no
additional support .OBJ files, you can test the overlay managers
with the MASM .OBJ files even if you do not have access to an
assembler such as MASM.
Link together the MASM .OBJ files, enclosing in parentheses the
modules you want to be overlays. Make sure that you use at
create at least one overlay or the overlay managers will not
work with the file you create. If you link the object files
together like this:
link linkovl+masmtest+(ov1+ov2)+(ov3),masmtest;
a standard .EXE file called MASMTEST.EXE will be created.
MASMTEST.EXE will include the root .EXE file MASMTEST comprised
of the code of the MASMTEST (and LINKOVL if it is used) object
module and will also include two overlay files appended to the
root .EXE file. One overlay file will contain the code of the
OV1 and OV2 modules, the other will contain the code of the OV3
module.
Typing MASMTEST at the command line causes the program to begin
execution. As program code is needed from an overlay, that
overlay is loaded from disk, if necessary, and program execution
continues.
Using LINKOVL.OBJ page 2 of 5
The amount of memory required to load the example file
MASMTEST.EXE, or any file created by LINK using overlays, is
equal to the size of the root file PLUS the size of the largest
overlay file PLUS any program overhead and dynamic memory
allocations made by the program plus OVL's overhead. This
brings up an important point. There is no advantage to only
using one overlay in a program since memory must be allocated
for it during program execution anyway. There is only the
disadvantage of the overlay overhead. In other words, while the
link commands:
link linkovl+masmtest+(ov1)+ov2+ov3,masmtest;
link linkovl+masmtest+ov1+(ov2+ov3),masmtest;
link linkovl+masmtest+(ov1+ov2+ov3),masmtest;
are all valid, there is no useful purpose served by linking
overlays in this fashion. Use two or more overlay files in the
link command.
An example of linking with two overlays is:
link linkovl+masmtest+(ov1)+(ov2)+ov3,masmtest;
Here there will be two overlay files containing the code of,
respectively, OV1 and OV2 and a root file containing the
MASMTEST, OV3, and LINKOVL code.
An example of linking with three overlay files is:
link /exepack linkovl+masmtest+(ov1)+(ov2)+(ov3),masmtest;
Three overlay files contain the code of OV1, OV2, and OV3. The
root file contains the MASMTEST and LINKOVL code. The /EXEPACK
or /E option of Microsoft's Overlay Linker shown in this example
may successfully be used with those programs suitable for the
option.
Another example of linking with two overlays is:
link linkovl+masmtest+(ov1+ov3)+(ov2),masmtest;
Two overlay files contain the code of OV1 and OV3, and OV2. The
root file contains the MASMTEST and LINKOVL code.
The only overlay combination not allowed by OVL is one where the
the initial entry code object module(s) -- in this case the
MASMTEST.OBJ and LINKOVL.OBJ modules -- are linked as an
overlay. Such startup code must be loaded in memory during the
beginning of the program's execution.
Using LINKOVL.OBJ page 3 of 5
LINKOVL.OBJ users with large root .EXE files, especially Clipper
programmers, should explore using EXEPACKed files. Using the
/EXEPACK option of Microsoft LINK will almost always result in a
significantly smaller .EXE file with large files than if it is
not used. Remember that the EXEPACKed files will not reduce the
memory requirements of a program.
The second set of files are examples using Turbo C. To use them
you need to have a C compiler compatible with the Turbo C source
files COW.C, FARM.C, HORSE.C, PIG.C, PIGLET.C, and SHEEP.C. No
.OBJ files are included due to the many different versions of C
compilers available; object modules for C are usually compiler
version specific. Compile the source files with your own
compiler.
OVL is put a little more to the test here because the code is
larger, parameters are passed to the overlays, a value is
returned from a function, and a command line argument can be
passed. Further, in one module, PIG.C, overlays can be nested
if the 'piglet' function that is called from it is located in a
different overlay file.
To create FARM.EXE with an overlay file containing the code of
HORSE and PIGLET and an overlay file containing the code of
COW, PIG, and SHEEP and a root containing the code of
FARM and the start up code of C0M, you would link like this,
assuming that the code has been compiled using the medium model:
link linkovl+c0m+farm+(horse+piglet)+(cow+pig+sheep),farm,
nul,emu+mathm+cm;
After you link the program try running it by typing FARM and
FARM MACDONALD to see the command line parameter in use. All of
the modules can be put in an overlay except for LINKOVL, C0M,
and FARM which contain startup code. Remember, you must use
Microsoft's LINK when linking this or any other Turbo C program
for use with OVL. The copy of TLINK included with Turbo C does
not support overlays.
The final set of examples are QuickBASIC 4.x files. Since
QuickBASIC programs need a QuickBASIC library to link correctly,
you must own or have access to QuickBASIC 4.x to try these
example files. Compile the source files with your BC.EXE
program. Almost all Basic module code commands are allowed in
overlays. The only known exception to allowed commands in an
overlaid Basic module is any form of CHAINing, either from or to
the module. Other than that, only the standard rules for use of
separate Basic modules apply.
Using LINKOVL.OBJ page 4 of 5
These QuickBASIC source files demonstrate how to use COMMON to
share variables between more than one module if one module is in
an overlay. If you have many variables in your COMMONs, you may
want to consider using $INCLUDE files to declare the variables.
This will eliminate the need to retype variables in all the
source modules if you make a change, and reduces the chance of
erroneous entry.
To really stretch OVL to its limits, link each of the BNEST
modules in a separate overlay, like this:
link linkovl+qbnest+(bnest1)+(bnest2)+(bnest3)+(bnest4),qbnest;
This forces OVL to nest overlays to its four level maximum.
To use your own QuickBASIC 4.x programs with overlays you should
compile the files using BC.EXE. Overlays will not work with the
runtime file BRUNxx.EXE so the /O option must be used to compile
QuickBASIC 4.x programs.
Feel free to try any permutation of overlays allowed by these
examples. OVL should work with any of them as long as you stay
within the restrictions already outlined. It is especially
important to remember not to put the initial entry code in an
overlay. The start up code must be in memory when the program
is first loaded, i.e. in the root code.
You may have noticed that these example files are all small
enough to fit into memory without overlays. You may even be
asking yourself how you really know that OVL is bringing the
overlays in as needed instead of sneaking everything in at once?
First, you can try running a file linked with overlays without
LINKOVL.OBJ. If you do this your computer will probably lock up
and need to be turned off or reset before it can be used again.
This is because your program is using interrupt 63 which OVL
hasn't initialized to point to code that manages the overlays.
Your program tries to transfer control to whatever random
address happens to be at the memory location that corresponds to
the address at interrupt 63, leading to unpredictable results.
The second test you can do is transfer the overlaid program to a
floppy and disable any disk caching. Now run the program. You
should see the floppy disk drive light come on during execution
of the example program as overlays are loaded from disk. For
maximum effect you may want to link the example program using as
many overlays as possible.
Using LINKOVL.OBJ page 5 of 5
It is important to understand how the use of overlays can affect
a program's performance. Time critical code should not be
divided between two overlays. Depending upon the speed of the
disk drive used and the size of the overlay file, the time to
load each overlay from disk can reach several seconds.
Extremely time critical code should also not be divided between
the root code and an overlay. The execution time overhead of
the overlay manager code can range from several microseconds up
to a few milliseconds depending upon the computer used to
run the overlaid program.
There is NO time penalty involved in calling routines FROM a
loaded overlay TO the root code or from one code module to
another WITHIN the same overlay file. There IS a time penalty
in calling routines FROM the root code TO an overlay file. This
time penalty will range from several microseconds with an
already loaded overlay file on a fast computer to several
seconds with an overlay file that needs to be loaded on a
computer with a slow disk drive.
Using OVLSTONE.OBJ page 1 of 2
USING OVLSTONE.OBJ and SCULPT.EXE
---------------------------------
The OVLSTONE overlay manager works in a very similar fashion to
the LINKOVL overlay manager (see the 'USING LINKOVL.OBJ'
section). However, OVLSTONE allows a programmer more -- and the
user less -- control over the behavior of the overlay manager
than LINKOVL does.
To use OVLSTONE, you must first run the SCULPT.EXE utility. The
SCULPT utility builds a data file called $$ODATA.OBJ that needs
to be linked in with OVLSTONE.OBJ when linking the overlaid
program.
SCULPT will display three fields that you can edit. The first
field is the Overlay File Path Environment String, with a
default value of PATH=. If you wish the OVLSTONE overlay
manager to search directories for overlay files or programs in a
different environment variable than PATH, change this field.
For example, if you wish OVLSTONE to search a environment
variable called OVERLAY for the overlay directories, enter
OVERLAY= in this field. If you do not wish OVLSTONE to search
any environment variable for overlay directories, fill the field
with blanks.
The second field is the Sign-on Banner Text. This is the text
that the OVLSTONE overlay manager will display while it
initially loads the overlaid program in addition to OVL'S
copyright message. The default text is "Loading....". If you
wish no text to be displayed during the overlaid program's
startup, enter a blank field.
Pressing the F9 key while in the Sign-on Banner Text field will
toggle the field input to an ASCII file specification to use for
the sign-on text. The default file name is SIGN-ON.TXT. If you
wish to use a different file name, change the field to the file
containing the text you wish to be displayed during the overlaid
program's startup. SCULPT will use up to the first 4096
characters in a file as the sign-on text. This text file is not
used during the overlaid program's startup, its text is loaded
by SCULPT and stored in the $$ODATA.OBJ file. If SCULPT cannot
find the ASCII file, it will give an error message.
For example, enter DOGGEREL.TXT in the field as an ASCII file
specification, replacing the default entry of SIGN-ON.TXT. Link
PROSTONE.OBJ and $$ODATA.OBJ in with your overlaid program.
While PROSTONE loads your program you will see OVL's copyright
message and a short verse about a pet who fully deserves the
abusive comments.
Using OVLSTONE.OBJ page 2 of 2
The third field is the Command Line Switch(es) field. Entries
in this field correspond to the runtime command line switches or
options used by the LINKOVL overlay manager. OVLSTONE does not
use or recognize runtime command line options. It uses the
entry or entries given in the SCULPT Command Line Switch(es)
field. The default command line option is /ZDOVERLAY.LOG.
After you have completed entering the information in SCULPT,
either press F10 to exit and save the changes made, or press the
Escape key to exit without saving the changes. If the F10 key
is pressed, SCULPT will create a file called $$ODATA.OBJ
containing the data you entered. To use OVLSTONE, you must link
in $$ODATA.OBJ. If you do not link in $$ODATA.OBJ with
OVLSTONE.OBJ, LINK will generate several unresolved externals
errors and the OVLSTONE overlay manager will not work properly.
The source to SCULPT.EXE is included in the OVL system as
SCULPT.C. SCULPT was written using version 2.0 of Borland's
Turbo C using object module record information in the MS-DOS
Encyclopedia.
OVL multiple overlay areas page 1 of 4
MULTIPLE OVERLAY AREAS (Advanced Operation)
-------------------------------------------
OVL supports two overlay areas. This allows you to have two
overlay files in memory at the same time, and for these overlay
files to be swapped in and out without the other being affected.
Why is this important? Suppose you have two sections of
initialization code in your program that operate independently
of each other. With only one overlay area, in order to reclaim
the dead space after initialization is completed, you have to
put both sections in one overlay file. Even after one section
is complete the other may still be in use, so each section must
take up memory until both are finished. With two overlay areas,
you could overlay one section as soon as it is complete,
allowing your program to run under smaller memory requirements.
Such an example only scratches the surface of how two overlay
areas can be used. Another example is using separate overlay
areas for code that runs two different peripherals. For
instance, one overlay area could be overlaid with a
user-selected printer driver, and the other with a particular
video driver. Other examples will probably come to mind once
you start thinking of ways to apply the idea.
Information about which overlay file loads in which overlay area
is passed via the command line. There are two switches or
options allowed, /A (or /a) and /B (or /b). Do not intermix
these switches with command line switches or options used by an
overlaid program when using the LINKOVL overlay manager.
If you are using the LINKOVL overlay manager, both LINKOVL's and
the program's command line switches come AFTER the program name,
with LINKOVL's switches coming first. To differentiate between
LINKOVL.OBJ and a program's command line switches you should use
OVL's //x option described in the 'COMMAND LINE OPTION //X'
section.
The OVLSTONE.OBJ overlay manager does not use or recognize
runtime command line switches. All command line switches should
be typed in the SCULPT.EXE utility.
Each switch should be followed by one or more numbers separated
by a comma, or range of numbers separated by a dash. These
numbers correspond to an overlay file. Overlay files are
numbered starting at 1 in the order that they were linked. The
/A and /B switches do not represent a particular overlay area,
but rather differentiate which overlay files are loaded in one
or the other overlay areas. The specific overlay area used to
load an overlay file is transparent to the enduser of the
program.
OVL multiple overlay areas page 2 of 4
All files in the switch containing the largest overlay file will
load in the standard overlay area designated by Microsoft LINK
during the linking process. All files listed in the other
switch load in the second overlay area. Such switches may be
either explicitly or implicitly given. Switches are explicit if
they are listed in the actual command line, e.g. /A1. They are
implicit if an explicit switch does not list all of the overlay
files; the remaining overlay files are assigned to the unlisted
(implicit) switch by default.
To demonstrate, if you linked the .OBJ files of the example
QBNEST files in this manner (OVLSTONE.OBJ users should replace the
'linkovl' object module with 'ovlstone+$$odata'):
link linkovl+qbnest+(bnest1)+(bnest2)+(bnest4+bnest3),
qbnest;
you would have three overlay files. Code for BNEST1 would be in
overlay file number 1, BNEST2 would be overlay file number 2,
and code for BNEST3 and BNEST4 would be in overlay file number
3. To run this program via OVL with the code from BNEST1,
BNEST3, and BNEST4 in one overlay area and BNEST2 in the other,
you would type:
QBNEST /A1,3 /B2
when using LINKOVL or
QBNEST
and specify a command line of /A1,3 /B2 in the SCULPT utility
when using OVLSTONE.
In this example, overlay files 1 and 3 load in the standard
overlay area, since overlay file 3 is the largest, and overlay
file 2 loads in the second overlay area. Because the overlay
switches do not correspond to an actual overlay area, the
following command line would give exactly the same results, if
you are using LINKOVL.OBJ as the overlay manager:
QBNEST /B1,3 /A2
OVLSTONE users would specify a command line of /B1,3 /A2 in
sculpt.
NOTE: Further examples in this documentation will assume use of
the LINKOVL.OBJ overlay manager unless otherwise noted. If you
are using the OVLSTONE.OBJ overlay manager, substitute the shown
command line options with the identical SCULPT.EXE Command Line
Switch entries and in link examples replace LINKOVL with
OVLSTONE+$$ODATA.
OVL multiple overlay areas page 3 of 4
Since any overlay files not listed with a switch are assigned to
the switch not used, this command line would work identically to
the previous two examples with LINKOVL.OBJ:
QBNEST /A1,3
The /B2 is implied by this command line. This is why, if you
use both the /A and /B switch of OVL, you MUST list all overlay
files in the switches. Otherwise, when OVL attempts to assign
the overlay files not listed to an unused overlay area it finds
both overlay areas used and returns an invalid overlay switch
value error. Using the same example:
QBNEST /A1 /B2
results in an invalid overlay switch value error because overlay
file 3 is not listed and there are no unused overlay areas to
assign it to.
If all of the overlay files are listed with one switch, the
advanced option second overlay area is effectively defeated. In
other words, if you put all of your overlay files in one overlay
area there isn't any reason to have the second overlay area.
While this may sound trite, it is relatively easy to overlook if
you are depending upon an implicit switch. For instance, the
command line:
QBNEST /A1-3
is identical to:
QBNEST
and the second overlay area is not used. Remember that ranges
can be represented by a dash, so that /A1-3 is the same as
/A1,2,3 (and /A1,2-3 or /A1-2,3 as well).
Included with the OVL files is an program called MULTEST.EXE,
created from the MASM source files MULTEST.ASM, MULTA.ASM,
MULTB.ASM, MULTC.ASM, and MULTD.ASM. The MULTEST.EXE program
provides a graphic demonstration of the power of two overlay
areas. MULTEST.EXE has been padded with 160,000 extra bytes to
increase load time to simulate operation under large file
conditions. The size of the resultant file also shows the
overlay managers' ability to handle overlay files greater than
64K. MULTEST.EXE was created with two overlay files using the
LINK command:
link linkovl+multest+(multa+multb)+(multc+multd),multest;
To best demonstrate the program, transfer a copy of MULTEST.EXE
to a floppy disk and disable any disk caching.
OVL multiple overlay areas page 4 of 4
First try basic OVL operation, that is, type MULTEST. After the
program loads and displays the prompt, when you press the 'A',
'B', 'C', or 'D' keys the floppy disk drive light will come on
as overlays are loaded. For example, if you first press the 'A'
key, overlay file 1 will load from disk into memory. At that
point neither an 'A' or 'B' keypress will required a disk access
because the overlay containing the code for process 'A' and 'B'
is in memory. If you press 'C' or 'D', the disk drive will be
accessed again to load in overlay file 2. Then either 'C' or
'D' can be pressed without accessing the drive, but an 'A' or
'B' keypress will reload overlay file 1.
In short, under this arrangement 'C' and 'D' keypresses will
swap out the overlay file containing the code for processes 'A'
and 'B', and 'A' and 'B' keypresses will swap out the overlay
file containing the code for the 'C' and 'D' processes.
Now try typing MULTEST /A1. This will cause overlay file 1 to
load in one overlay area when its code is needed and overlay
file 2 to load in the other. The disk drive will be accessed
the first time you press 'A' or 'B' and the first time you press
'C' or 'D', but once both overlay files are loaded there will be
no more disk accesses -- no matter which of the four keys you
press and no matter what the order.
A nice feature of multiple overlay areas and other command line
options with LINKOVL is that their use is optionally under the
control of the enduser. The enduser may dynamically configure
the program to best fit the memory and speed requirements of a
specific environment without the need to relink the program, or
access the object files. In fact, when using multiple overlay
areas -- unlike when using one overlay area -- assigning only
one overlay to a particular overlay area can be advantageous.
Endusers with large amounts of free memory will probably wish to
use two overlay areas to keep as much code in memory as
possible. Those with less free memory may only be able to use
one overlay area, paying for the lower memory requirement with
more frequent disk accesses. The identical version of a program
can be used in both cases. Only the command line arguments
passed to it at runtime will differ.
OVLSTONE, on the other hand, is better for those who know what
overlay manager options they want their endusers to have and who
do not need the flexibility of runtime configuration. When
using OVLSTONE, endusers do not have responsibility of supplying
the proper command line options. Of course, use of the OVLSTONE
overlay manager is also required if a loading message or overlay
directory environment variable different from PATH is needed.
Command line option //x page 1 of 2
COMMAND LINE OPTION //x (Advanced Operation)
--------------------------------------------
Programs that use the LINKOVL.OBJ overlay manager and command
line options that begin with a '/' need a way to distinguish
between the LINKOVL options and the program options. This is
handled by OVL's //x option, where 'x' can be any printable
character except for the DOS special characters for input and
output redirection and command piping, i.e. <, >, and |.
The //x option changes the character recognized by OVL as the
beginning of an option to a different character. OVL stops
scanning for options as soon as it encounters a character which
is not one of its options, passing the remaining command line
to the overlaid program.
For example, if you had a program named RUNME.EXE that was
linked with LINKOVL.OBJ and you needed to pass the command line
options or switches /DEBUG and /X to the program and the command
line options /A3 and /B1-2 to LINKOVL, you would use this command:
RUNME /A3 /B1-2 //$ /DEBUG /X
The //$ part of the command line directs LINKOVL to look for the
'$' character for any further command line options. When
LINKOVL encounters the next '/' character, it stops looking for
options and passes the remaining command line, /DEBUG /X, to the
overlaid program. The '$' character can be replaced in this
example by any other character that would serve the purpose of
forcing LINKOVL to stop scanning when it reaches a program
option.
Even if you only need to pass command line options beginning
with a '/' to a program and not LINKOVL, you must still use the
//x option. Otherwise, LINKOVL has no way of determining that a
particular option is not meant for its interpretation. If you
have a program that needs the command line option /BELL, but you
wish to pass no options to LINKOVL, you would use this command:
RUNME //x /BELL
Again, the 'x' character can be replaced by other characters if
it is necessary or desireable.
Command line option //x page 2 of 2
The //x option can be used more than once on a particular
command line, changing the character OVL scans for as a
beginning to an option each time it is encountered. For
example, if you wish to pass the command line options
/ZDLOGFILE, /A1,2 and /ZS to OVL and the command line options
/NON, /QS, and /LO to an overlaid program called RUNME, you
could do it in this fashion:
RUNME //* *ZDLOGFILE **& &A1,2 &&+ +ZS ++/ //# /NON /QS /LO
Of course this is more complicated than necessary. A more
mundane approach would be:
RUNME /ZDLOGFILE /A1,2 /ZS //# /NON /QS /LO
the //# switch or option forcing OVL to stop scanning with the
next '/' character.
Although the OVLSTONE.OBJ overlay manager supports the //x
option for consistency, there is no need to use it.
Other command line options page 1 of 2
OTHER COMMAND LINE OPTIONS (Advanced Operation)
-----------------------------------------------
There are three other command line options that the OVL overlay
managers can use. The three options are /ZD<filename>, /ZBn,
and /ZS. Following is a description of each.
(1) The /ZD<filename> option allows a user to specify a debug
file that will timestamp and log the loading, access, or swap of
each overlay.
For example, to log overlays for a program called MYPROG.EXE
with two overlay areas into a file called MYPROG.LOG, you could
type MYPROG /A1 /B2-4 /ZDMYPROG.LOG at the DOS prompt. A
typical debugging log file for such a situation might look like
this:
09:15:06 Overlay 01 Loaded
09:15:35 Overlay 02 Loaded
09:16:07 Overlay 03 Swapped out Overlay 02
09:17:12 Overlay 04 Swapped out Overlay 03
09:20:14 Overlay 03 Swapped out Overlay 04
09:24:00 Overlay 02 Swapped out Overlay 03
09:33:53 Overlay 01 Accessed
09:39:32 Overlay 02 Accessed
09:54:17 Overlay 04 Swapped out Overlay 02
09:55:40 Overlay 04 Accessed
The timestamp comes first, then the overlay number being
manipulated and the number of the overlay being swapped out, if
any. An overlay may either LOAD into an empty overlay area and
be accessed, SWAP out another overlay in the overlay area it
loads into and be accessed, or simply be ACCESSED, having been
loaded during a previous call to the overlay.
Devices such as LPT1 or CON are valid filenames for a log file.
Preexisting log files will be appended to, rather than
overwritten.
There is no space between /ZD and the filename when using
this option.
Other command line options page 2 of 2
(2) The /ZBn option shrinks or increases the size of the buffer
OVL allocates for reading the relocation table items in an .EXE
file header.
If the buffer allocation is too small, overlays will take
somewhat longer to load because OVL will need to access the disk
more than once to read in all of a relocation table. If the
buffer is too large, memory is wasted. The 'n' following /ZB is
the number of kilobytes allocated to the buffer and can be any
number from 3 to 8. The default buffer size is 4K (/ZB4). This
is a good compromise value and probably should not be changed
unless you understand what the relocation table in a
.EXE file is. Overlay files with a very large relocation table
may load somewhat faster if the buffer size is set to its
maximum size of 8K, i.e. /ZB8. Or, you can reduce the overlay
managers' memory requirements by using a table size of 3K
(/ZB3). PROVL expands the allowed 'n' from 1 to 32.
If you wish to use the /ZB option, the MAPOVL.EXE utility
described in the 'Using MAPOVL.EXE' section may be helpful in
selecting an appropriate buffer size for your application.
Do NOT insert a space between /ZB and the number when specifying
this option.
(3) The /ZS option directs OVL to recognize and load overlays
from separate files.
You must use the SPLIT.EXE utility to generate individual
overlay files from an overlaid program created by Microsoft
LINK. See the 'USING THE SPLIT.EXE UTILITY' section in this
manual for more information on separate overlay files and the
SPLIT utility.
NOTE: All command line options are case insensitive.
Using SPLIT.EXE page 1 of 1
USING SPLIT.EXE -- A Utility to Allow Separate Overlay Files
------------------------------------------------------------
SPLIT.EXE is a utility that splits off the overlay .EXE files
normally appended to the root .EXE file by Microsoft LINK.
These overlay files have the same name as the root .EXE file
with an extension of '001', '002', and so on up to the number of
overlay files in the program. You must use the /ZS option of
OVL if you split separate overlay files off of the main .EXE
file. Otherwise OVL will abort with a "Bad EXE file signature."
error when it searches for an overlay at the end of the root
.EXE file.
To use the SPLIT utility, type SPLIT and press return. SPLIT
prompts you for name of the file to split, then splits up the
files, and terminates with a message showing how many overlay
files were created. You may bypass the filename question by
typing SPLIT <program name>, e.g. SPLIT MYPROG, if MYPROG.EXE is
the overlaid program to split up. Accidentally running SPLIT on
an already split up .EXE file is harmless, SPLIT will find no
overlay files to split off and simply terminate.
Separate overlay files are most useful when you need to avoid
one large program .EXE file, e.g. due to available storage space
on floppy disk. In addition, since OVL automatically searches
the entire PATH environment string for an overlay file if it
doesn't find the file in the current directory, it is also
possible to run overlays off of a different disk drive when the
/ZS option is used.
Because of the small increase in development time involved in
running SPLIT, it is recommended that you not bother with
splitting your program into separate overlay files until it is
ready for enduser operation.
The source to SPLIT.EXE has been included in the OVL package for
your study or amusement. The source file is SPLIT.C. SPLIT was
written using version 2.0 of Borland's Turbo C.
Using MAPOVL.EXE page 1 of 2
USING MAPOVL.EXE
----------------
The utility MAPOVL serves two purposes. It reports on the
actual code size of overlay files without their .EXE header to
allow you to see what the memory requirements for particular
overlay file and overlay area configurations are. MAPOVL also
displays the number of relocation table items in each overlay
file so that you can choose the best /ZBn option for your
particular situation.
To use the MAPOVL utility, type MAPOVL and press return.
MAPOVL prompts you for the name of the overlaid file to
report on. As with SPLIT.EXE, you may bypass the filename
question by typing MAPOVL <program name>. Do not use
MAPOVL on a program which has already been had SPLIT.EXE
run on it. MAPOVL searches for overlay files at the end of
the root .EXE file.
Following is sample output from MAPOVL for a file called
TEST.EXE with three overlays:
Report on file test.exe
=======================
DATE: 5/09/1989
TIME: 23:22:40
Root file: File size 87552 (15600 hex) bytes
Relocation table 19 (13 hex) items, 76 (4c hex) bytes
Unaffected by /ZBn option
Overlay file 1: File size 40448 (9e00 hex) bytes
Relocation table 5803 (16ab hex) items, 23212 (5aac hex) bytes
/ZBn option requires 'n' of 5 for no table reload
Overlay file 2: File size 80384 (13a00 hex) bytes
Relocation table 6 (6 hex) items, 24 (18 hex) bytes
/ZBn option requires 'n' of 1 for no table reload
Overlay file 3: File size 40448 (9e00 hex) bytes
Relocation table 10003 (2713 hex) items, 40012 (9c4c hex) bytes
/ZBn option requires 'n' of 40 for no table reload
Overlay file 2 always loads into the standard overlay area.
Report complete: 3 overlay files
After printing the report header and the date and time of the
MAPOVL run, MAPOVL reports on the root file. This provides no
information about overlays, but it is handy for comparison of
root to overlay file size.
Using MAPOVL.EXE page 2 of 2
Following the root file report, MAPOVL displays information
about each overlay file that it finds. First it reports on
the true file size of the overlay file rounded up to the
next 512 byte page. This is the amount of memory that an
overlay file will take up when loaded into an overlay area.
Each overlay area will be large enough to accommodate the
largest overlay file that loads there.
After the file size information, MAPOVL displays the number
of relocation table items and the byte size of the
relocation table. The byte size will always be four times
the count of items. MAPOVL uses this information to
calculate the minimum /ZBn size that OVL needs to avoid
having to reload the relocation table, slowing down the
speed at which an overlay loads from disk. /ZBn sizes are not
cumulative, that is, if one file requires an 'n' of 5 for no
table reload and another requires an 'n' of 6, /ZB6 will avoid a
reload for either file. If you have the memory to spare, you
should use the /ZBn listed for best program performance. If the
recommended /ZBn is higher or lower than the allowed range, use
the highest or lowest value allowed.
Unless an overlay file is very large or has an extraordinary
number of relocation table items, you will generally find that
the default /ZB4 is sufficient to avoid a table reload for most
situations. Even if a reload is necessary, the extra delay is
usually less than a second and often not noticeable to the
program operator.
The largest overlay always loads into the standard overlay
area allocated by LINK. MAPOVL shows which overlay loads
into the standard overlay area. This standard overlay area
is a part of the root file size. No additional memory
allocations are needed for this overlay area, so the worst case
memory allocation for the second overlay area will never be more
than the size of the second largest overlay file, and then only
if it loads in a different overlay area from the largest overlay
file.
The source to MAPOVL.EXE has also been included in the OVL
package for those interested. The source file is MAPOVL.C.
MAPOVL was written using version 2.0 of Borland's Turbo C.
Using PRONK.EXE page 1 of 3
USING PRONK.EXE
---------------
PRONK is an object module preprocessor for Microsoft's Overlay
Linker that allows LINK to properly set up indirect calls to
overlay files. Clipper programmers MUST use PRONK.EXE in
conjunction with OVL and any overlaid program. It is unknown
whether PRONK.EXE works other overlay managers, such as the one
that comes with Microsoft C.
This 2.x version of PRONK greatly enhances the functionality of
PRONK 1.x versions by removing the need to save and restore
object modules modified by PRONK.
PRONK directly reads and writes to object modules, creating
an object module called $$MD.OBJ that is linked in with the
other object modules in the link command. Pass the same
command line to PRONK that you normally pass to Microsoft
LINK. After PRONK has altered and created the necessary
object modules, it automatically invokes LINK with the same
command line passed to it except for '+$$md' added to the
object file list. The '+$$md' will be inserted as the
second file in the object file list.
The example PRTEST.ASM, PTEST2.ASM, and PTEST3.ASM source files
show a variety of indirect calls to procedures. If there were
no indirect calls to procedures and you wanted to put PTEST2.OBJ
and PTEST3.OBJ in an overlay, you could link in this fashion:
link linkovl+prtest+(ptest2)+(ptest3),prtest;
However since the object modules in this example contain
indirect calls to overlay procedures, linking in this manner
with Microsoft's Overlay Linker will not work. Running PRTEST
after linking like this will cause improper behavior when an
indirect call to an overlay is made, and possibly lock up the
computer.
PRONK may be used in such cases to allow proper program
operation. This command line should be used for the previous
example:
pronk linkovl+prtest+(ptest2)+(ptest3),prtest;
While PRONK is running it displays the names of the object
modules that it has modified. Not all object modules may need
to be modified by PRONK, often it is necessary to modify only
one or two. After PRONK has finished, it automatically loads
and runs LINK, displaying the command line it passes to LINK.
The command line in this example is:
link linkovl+$$md+prtest+(ptest2)+(ptest3),prtest;
Using PRONK.EXE page 2 of 3
The PRTEST.EXE program created by PRONK should overlay
correctly. Notice that PRONK has created and added the file
$$MD to the object file list passed to LINK. This object file
contains direct calls to publicly defined overlay procedures or
functions, allowing LINK to properly set up the overlay manager
interrupt. Any preexisting object file called $$MD.OBJ in your
current directory will be overwritten.
PRONK also works correctly with response files or options in the
LINK command line. The following command is valid syntax for
PRONK assuming that the PRRSP.LNK file exists and is in the
current directory:
pronk /exepack /nod linkovl+@prrsp.lnk;
Note that if you use a response file that contains more than the
object file list, this is, a map file, program name, or library
list, you MUST place at least one object module outside of the
response file. PRONK always tries to place $$md.obj second in
the object file list and such an arrangement will not work
correctly if the first entry in the list is a response file
which completes the object file list.
PRONK correctly handles output file redirection for Microsoft
LINK, although PRONK's copyright message, object modules
modified message, and the command line passed to MS LINK will
appear first in the redirected file. PRONK will return an
errorlevel of 1 to a batch file if it aborts with an error.
PRONK reads each object file into memory and then rewrites it if
any changes are necessary. If PRONK is interrupted in the
middle of its operation due to power failure or other
circumstance, the possibility exists that an object module PRONK
was writing to has been corrupted. PRONK attempts to warn you
of circumstances when object modules may have been corrupted,
but such warning should not be depended upon as a surety. If
PRONK abnormally aborts, check the object modules modified list
to see what files were modified and recompile or restore from
backup those that were modified. IF YOU HAVE ANY IRREPLACEABLE
OBJECT MODULES, MAKE SURE THAT YOU HAVE ONE OR MORE BACKUP
COPIES OF THOSE MODULES BESIDES THE COPY PRONK IS WORKING WITH.
Unlike earlier versions of PRONK you can safely rerun PRONK with
the same program object modules that have been modified on a
previous PRONK pass. PRONK will automatically recognize object
modules that it has previously modified and make any necessary
adjustments without operator intervention. There is no need to
save and restore the original object module as there there was
with versions 1.x of PRONK.
Because of this enhancement, modified object modules may
slightly increase in size. This size increase will not be
reflected in the .EXE file created from the object modules. It
will remain the same size as before.
Using PRONK.EXE page 3 of 3
You need not rerun PRONK if you change an object module
unmodified by PRONK in a previous pass UNLESS the object module
has been changed to call a procedure indirectly (always indirect
with Clipper) in an overlay object module. Be sure to link in
the last created version of $$MD.OBJ, however.
Be aware that PRONK changes code labels in modified object
modules. If PRONK or LINK aborts with an error, you may see
error messages containing code labels or procedure names that
were not used in the overlaid program's source code. Avoid
using the global labels or names '___AAA' through '___BMI' in
your program. Only the leading three underscores and letters
are used by the changed labels. Three underscore characters
before numbers and other legal name characters can be safely
used in a program's source code.
The code overhead when using PRONK amounts to 6 bytes per public
name in the overlay modules, with a maximum capability of
handling 1023 public names. At worst, this will add 6138 bytes
to your root code size.
The source code to PRONK is available for a fee. PRONK was
written in Turbo C, version 2.0. To order the source code, send
$23.00 to the address in the PROVL section immediately
following. The ordering instructions for the PROVL package and
PRONK's source code are the same. The PROVL commercial overlay
manager package does not include the PRONK source code and the
$5.00 discount can only be applied once, even if both are
ordered.
PROVL -- An enhanced version of OVL page 1 of 2
PROVL -- An Enhanced Version of OVL
-----------------------------------
If you wish to sell a program that uses OVL to operate, or if
you just want a more powerful version of OVL, an enhanced
version of OVL called PROVL can be purchased for $80. You may
reduce this amount by five dollars (to $75.00) if you send me
the name and location of the bulletin board, software
distributor, or place where you received your copy of OVL. If
someone else gave you the copy of OVL, ask him or her where they
got it from. The reason for the $5.00 discount is that this
information is valuable to me in determining distribution
strategies.
PROVL adds the following enhancements to OVL:
1. PROVL supports up to nine overlay areas.
2. PROVL allows up to the Microsoft Overlay Linker maximum
of 63 overlays.
3. The depth that overlays can nest to is increased to 32
levels with PROVL.
4. PROVL works with any overlay interrupt specified by the
/O option of LINK.
5. PROVL expands the allowed buffer size of the /ZBn
option to 1K through 32K. For some overlay files this
can reduce the overlay manager's overhead by up to 2K
with no side effects. Others may load faster with the
higher range /ZBn numbers.
PROVL also dispenses with the runtime copyright notice. This
removal of the runtime copyright notice does not suggest, and
should not be taken to suggest, that PROVL is not copyrighted.
A potentially distracting message is simply not displayed.
A bound manual is provided with PROVL for your convenience.
No royalties are charged for use of PROVL. This means that you
need only purchase a single version of PROVL for use with your
program no matter how many copies of your program you
distribute. Purchase of PROVL entitles the purchaser to
telephone support. I reserve the right to require that all
calls be at the purchaser's expense.
PROVL -- An enhanced version of OVL page 2 of 2
For those with particular needs, customized or special versions
of PROVL are available. One version allows a user to link in
his or her own custom error-handler if a DOS error occurs inside
of the overlay manager. There is no extra charge for a
customized change to the standard version of PROVL IF the change
is deemed to have potential use for other PROVL users and is not
too major. Very specialized or large changes will cost more
than the standard PROVL version. Please contact me if you
require a special version of PROVL.
PROVL's source code is NOT available. If you need or would like
the source code to an overlay manager, please read the
LOVR/PLOVR section immediately following this section.
Purchase of PROVL is MANDATORY if you wish to use a version of
OVL for distribution with a commercial or potentially commercial
application -- including programs distributed as shareware.
PROVL is the only version of the overlay manager permitted for
use with such applications and programs. OVL's copyright
license does not legally permit its commercial use. Please
abide by these reasonable terms. Thank you.
To purchase PROVL, send $80.00 in US dollars -- $75.00 if you
include a description of where you heard of PROVL -- by check or
money order with your shipping address to:
Michael E. Devore
Devore Software & Consulting
403 West Charles
Champaign, IL 61820
Please state your preference for either 360K 5 1/4 or 720K 3 1/2
inch diskettes. Overseas orders please include an additional $8
for shipping. Federal Express overnight orders please enclose
an additional $11 for shipping (remember that you cannot use a
P.O. Box with Federal Express). Other orders will be shipped
first class mail with no additional shipping charge.
All information contained herein, including the cost of PROVL,
is subject to change without notice.
PROVL copyright 1988, 1989 by Michael E. Devore
Too large! Too complicated! page 1 of 1
TOO LARGE! DOESN'T WORK WITH MY DEBUGGER!
TOO COMPLICATED! PROVL TOO EXPENSIVE!
------------------------------------------
There exists a cousin program to OVL, called LOVR, current
version 1.14b. LOVR is strictly a linkable overlay manager with
no command line options, e.g. it supports neither multiple
overlay areas nor separate overlay files. As a consequence,
LOVR takes up less memory than OVL, approximately 9K.
LOVR uses less complicated techniques than the overlay managers
in the OVL package. For example, it simply integrates into the
program's code without reloading the overlaid program as the OVL
overlay managers do. More technically speaking, LINKOVL and
OVLSTONE use the DOS EXEC function and LOVR does not. Such an
approach may work better with the particular debugger you use on
your programs.
Since LOVR supports no extra options, it is most useful for
those with more modest overlay manager needs who do not require
the extra power of OVL.
If you wish a copy of LOVR and you have been unsuccessful in
obtaining a copy, you may send $6.00 to cover shipping and
handling for the latest version to the shipping address in the
PROVL section. No $5.00 discount applies.
LOVR also has an enhanced commercial version, called PLOVR.
PLOVR adds similar non-command line option enhancements to LOVR
that PROVL does to OVL. A small manual is provided with PLOVR
as well. Additionally, the PLOVR package includes a smaller
copy of PLOVR.OBJ called SPLOVR.OBJ, which takes up 5K of
program space in the root code, instead of 9K. The trade-off
for the decrease in space is an occasional increase in time to
load an overlay from disk in some circumstances, but SPLOVR can
be useful for those running close to the memory space limit even
with overlays. PLOVR costs $50, less a $5 discount if you
include a description of where you heard of PLOVR (i.e. where
you got this OVL package) when you order. The ordering
instructions for the PLOVR package and the PROVL package are the
same and can be found in the PROVL section immediately
preceding.
PLOVR's source code is available for additional cost with a
signed license agreement. The 8088 assembly language source
code is fully documented with comments. Please contact me for
details. PROVL's source code is NOT available.
Trouble-shooting page 1 of 3
TROUBLE-SHOOTING
----------------
Check to make sure that you have compiled your program properly.
Turbo C and MASM users must compile their source files using a
large or far code memory model. OVL will not work under a small
or near code memory model.
Use a recent version of LINK when linking overlays for OVL. OVL
was tested with LINK versions 3.05, 3.06, 3.60, 3.61, 3.64, and
3.69 and 5.01.20. Some 2.x versions of LINK may not work
properly. TLINK, PLINK, or other proprietary linkers will not
work with OVL; you must use Microsoft's linker. In addition, if
you experience problems, try linking with a different version of
LINK.EXE -- at least one version has errors that causes improper
operation when programs are linked with overlays.
Check your link syntax, making sure that neither LINKOVL.OBJ or
OVLSTONE.OBJ nor the initial entry or main program module is in
an overlay, and that you are not exceeding twelve overlay files
or nesting overlays deeper than four levels.
Link LINKOVL.OBJ or OVLSTONE.OBJ in as the first object module
of Microsoft LINK's object file list. Otherwise, memory
requirements for the overlay manager will increase, possibly
enough to exceed available memory.
If you use the OVLSTONE.OBJ overlay manager, remember to link in
the $$ODATA.OBJ file created by SCULPT. Unlike the overlay
managers, the $$ODATA.OBJ file is not position dependent in the
LINK object file list.
Carefully read the SPECIFICATIONS AND REQUIREMENTS sections to
make sure that you are using the OVL programs in accordance with
their operating requirements. One possible mistake for those
using OVL with 'C' or assembly language is to indirectly call a
function or procedure in one overlay from another or from the
root to an overlay without using PRONK on the object modules.
Clipper users must always use PRONK, since all of Clipper's
calls to overlay procedures are made indirectly. Microsoft LINK
requires direct calls to overlay procedures for it to correctly
set up the overlay manager interrupts.
Clipper users should not use macros in an overlay that calls
procedures in an unloaded overlay since macros bypass the
overlay manager. Macros may call procedures in the root, the
same overlay, or another overlay if the other overlay is also
loaded in memory (this requires using multiple overlay areas).
Trouble-shooting page 2 of 3
Use of OVL's advanced options and support utilities brings with
it more possibilities of operator error. If you are using
multiple overlay areas, it is important to understand that all
overlay files not listed in an OVL command line switch are
assigned to a different overlay area from the files listed in
the switch. Check that your switches and switch values match
the rules outlined in the 'USING MULTIPLE OVERLAY AREAS' section
of this manual.
LINKOVL.OBJ users who wish to pass command line options to an
overlaid program via the '/' character must use the '//x' option
of OVL to avoid confusing LINKOVL into an attempt to take the
overlaid program's command line options as its own. All command
line options for an overlaid program must come AFTER LINKOVL's
own command line options.
Since OVL will search all directories in the PATH or
SCULPT-defined environment variable when attempting to find a
program containing an overlay file, it is important not to have
another file with the same name as the overlay file in a
directory earlier in the PATH variable, if the overlaid file is
not in the current directory.
If you use the utility SPLIT.EXE, remember to use the /ZS option
of OVL. Do not use the /ZS option if the most recent version of
the overlaid program has not been run through SPLIT. Old
versions of separate overlay files will cause problems with a
non-split program that inadvertently has the /ZS switch in the
command line.
If you are sure that you are compiling and linking properly and
operating OVL within its specifications and requirements, but
you still experience problems, make sure that the error is not
in your program. If memory size allows, compile your program
without overlays and test it. If the size of your program is
too large for all of it to fit in memory, try to compile only
the code that is giving you problems and see if it works
correctly without overlays.
If your program still fails after you have eliminated all
suspects except for OVL, please contact me so I can fix the
problem as soon as possible. However, I will need to know the
circumstances. What error message, if any, does OVL display?
What version and options of OVL were used? What version and
options of LINK were used? What hardware and software
configuration was your machine running under when the error
occurred? What language was the program written in? If I deem
it necessary to locate the error, I may request a copy of the
program that causes OVL to operate incorrectly. This copy will
be held in the strictest confidence and either returned or
destroyed after I am through testing. You, of course, will have
the option of refusing the request, although this will probably
mean a delayed, or no, fix for the problem.
Trouble-shooting page 3 of 3
If an error is in OVL and you are the first person to find the
error, I will send you a free corrected version as soon as it is
available. The corrected version will either be sent by e-mail
if possible, or regular USPS mail if not. If you are not the
first person to find the error and do not wish to wait for the
corrected version to reach general distribution channels, you
may send $6.00 to cover shipping and handling for the latest
version to the address below.
If you subscribe to either the CompuServe Information Service or
the GEnie Information Service, you can send me electronic mail
at the appropriate e-mail address below. Barring vacation or
unusual circumstances, I check in to the CIS and GEnie services
at least once a week -- usually more frequently. Your e-mail
will be acknowledged as soon as I receive it.
If you do not subscribe to either CompuServe or GEnie you should
contact me through USPS mail at the address given at the end of
this section.
The realities of life and need for income being what they are,
my billable work and support of my commercial software has
priority over fixes to and questions concerning OVL or LOVR. If
I have a full work schedule, a fix or question may take more
time to respond to than either you or I would prefer. This is
unfortunate, but unavoidable.
MAILING ADDRESS:
Michael E. Devore
Devore Software & Consulting
403 West Charles
Champaign, IL 61820
E-MAIL ADDRESSES:
CompuServe 71540,62
GEnie MDEVORE
(BIX sign-on has been cancelled, do not use)
Overlay Technical Documentation page 1 of 2
OVERLAY TECHNICAL DOCUMENTATION
-------------------------------
It is not necessary to read or understand this part of the OVL
documentation to use OVL. This technical documentation is
included for those who wish to know more information about how
overlay calls are set up by Microsoft LINK.
When you link a program with overlays, LINK sets up direct calls
to code in the overlays in a special way. All of these calls
are replaced with an interrupt. By LINK default the interrupt
is 63 decimal or 3f hexadecimal, although the interrupt can be
changed using the /O or /OVERLAYINTERRUPT LINK option. This
option is not supported by OVL, although PROVL does support it.
Immediately following the interrupt inserted by LINK are three
bytes of data. The first byte is used by the overlay manager as
an offset into an table found in the root .EXE code (usually
located at the end of the root) that determines which overlay
should be loaded into memory. The second two bytes give the
value that the Instruction Pointer (IP) should have when a jump
to the overlay code is executed. When the overlay manager is
called by the interrupt, it needs to adjust the return address
to point past these three bytes.
The remaining information that the overlay manager needs can
usually be found at the end of the root .EXE file. Note that an
overlaid .EXE program has overlay .EXE files appended to the
root .EXE file. Also, at least one non-default option of MS
LINK, the /EXEPACK option places additional information at the
end of the root .EXE file.
Each overlay file has its own header that follows the standard
format of normal .EXE file headers, including items in a
relocation table that need to have fixups performed on them.
The overlay information in the root file corresponds to data in
the OVERLAY_DATA segment created by MS LINK. All of the data
has a MS LINK internal variable name, although these names are
documented nowhere by Microsoft to the best of my knowledge.
The names are prefixed with a '$$' and can be seen if you look
at a binary dump of LINK.EXE. The information that the root
.EXE has is as follows:
1 word containing the count of all segments in overlay
files plus one.
1 word containing the total .EXE files in the main .EXE
file. This will equal the number of overlay files plus one
for the root.
1 zero word. This word is fixed up to the program load
segment when the program is loaded into memory.
Overlay Technical Documentation page 2 of 2
A table with entries for each overlay that, when added to
the root program load segment, provide the value the Code
Segment (CS) should have when a jump to the overlay code is
executed. MS LINK fixes up the values in this table as
well. If using LINK's internal '$$' variables during
runtime, the need to add in the root program load segment
value is negated.
1 zero word.
A table that uses the first byte following the interrupt in
the calling code for an offset. The entries in the table
determine which overlay has the necessary code and should
be loaded in memory, if it isn't loaded already.
Variable number of zero bytes.
The name of the main .EXE file that normally has all of the
overlay files appended to it. This will not be true if you
have used the SPLIT.EXE program to create separate overlay
files.
Variable number of zero bytes. These bytes have a
corresponding MS LINK internal variable name, but their
use, if any, is unknown to me.
The number of the interrupt LINK inserts in the program
code that is vectored to the overlay manager code.
This information has remained stable for Microsoft LINK
versions 3.05 through 3.69. It may change for future versions
of Microsoft LINK.
The information presented here is solely for your interest and
entertainment. Michael E. Devore makes no claims or guarantees
of the accuracy of this information. Use of this information is
strictly at your own risk.
Comments and Miscellany page 1 of 2
COMMENTS and MISCELLANY
-----------------------
OVL is shareware. No, that does not mean I am going to request
or require you to send money if you use it longer than a
reasonable trying out period. What it means is that OVL is a
zero dollar registration, copyrighted program with some use
restrictions, most notably that it is only for noncommercial
use. If you use, or plan to use, OVL in one or more programs
over a period of a month or more, then you should register it.
To register, all I ask is that you send me your home address and
the name and location of the bulletin board, software
distributor, or place where you received your copy of OVL. If
someone else gave you the copy of OVL, ask him or her where they
got it from. You may send this information to me via US mail or
electronic mail.
I will not put your address on some mailing list or deluge you
with advertisements. The reason I ask for this information is
that it is very valuable to me. Knowing where OVL is being
distributed, what distribution sites are most successful, and
the address spread of those who frequent the distribution sites
is extremely helpful.
If you feel that you must reward me monetarily or you do not
wish to divulge where you got your copy of OVL for whatever
reason, then send me a letter with your return address and a
quarter (25 cents) inside as an alternate method to register
OVL. This will help cover the postage cost of those who send
letters asking for help without sending a self-addressed stamped
envelope and the overhead cost of receiving and answering e-mail
queries. Individually these costs are small, but they can (and
do) mount rapidly.
OVL should be powerful enough for most casual or part-time
programmers needing a solution to the problem of a program that
has gotten too large to fit in available memory. OVL is also
for professional programmers who have the same problem with a
personal application. Those who need a more powerful solution
or who wish to use this type of overlay manager for a commercial
application should be able to afford the enhanced PROVL version.
Such an approach is in keeping with my philosophy of allowing
those chronically short on cash to still have the benefits of
some programming tools. I have great sympathy for persons with
little money, having been in that position myself on more than
one occasion. This philosophy should not be interpreted as
support for piracy, nonpayment of shareware fees, or other
unethical acts. Nor should it be interpreted as precluding my
releasing other shareware with a fee-based registration in the
future. I just think it is pleasant that not all programs have
a price tag attached. OVL is one of many programs in this
category. Look around, despite what cynics (and purveyors of
high-priced software) may say, programs do not have to be
expensive to be good.
Comments and Miscellany page 2 of 2
OVL is written entirely in 8088, also known as 8086, assembly
language. I feel that this is necessary to achieve acceptable
speed and size overhead, especially with older computers, while
maintaining maximum compatibility. While some optimizations to
OVL's code can undoubtably be made, I am skeptical that a
significant decrease in code size is possible while retaining
all of its functionality.
If you have an idea for an improvement to OVL, a comment or
question about OVL, or even a complaint about OVL, please send
it to either my USPS mailing address or one of the e-mail
addresses below. I am receptive to new ideas and constructive
criticism. Your comments DO make a difference. Several
enhancements to OVL have come about due to user requests so
don't be shy about dropping me a postcard or sending
e-mail. I am also interested in what applications or other
languages you use OVL with.
OVL began as a grass-roots solution to the problem of a low-cost
overlay manager. I hope to maintain that attitude and never
acquire the arrogant traits exhibited by some software
developers and corporations. With your help, I plan to keep OVL
a viable, useful, low- or no-cost alternative to overpriced
software.
Michael E. Devore
Devore Software & Consulting
403 West Charles
Champaign, IL 61820
CompuServe 71540,62
GEnie MDEVORE
(BIX sign-on has been cancelled, do not use)
_______
____|__ | (tm)
--| | |-------------------
| ____|__ | Association of
| | |_| Shareware
|__| o | Professionals
-----| | |---------------------
|___|___| MEMBER
This program is produced by a member of the Association of
Shareware Professionals (ASP). ASP wants to make sure that the
shareware principle works for you. If you are unable to resolve
a shareware-related problem with an ASP member by contacting the
member directly, ASP may be able to help. The ASP Ombudsman can
help you resolve a dispute or problem with an ASP member, but
does not provide technical support for members' products. Please
write to the ASP Ombudsman at P.O. Box 5786, Bellevue, WA 98006
or send a Compuserve message via easyplex to ASP Ombudsman
70007,3536.
PRTEST.ASM
DOSSEG
.MODEL large
.STACK 100h
PUBLIC p2message,p3message
EXTRN p2:PROC,p3:PROC
.CODE
start:
mov ax,dgroup
mov ds,ax
mov dx,offset message
mov ah,9
int 21h
mov ax,offset p3
mov word ptr jmp_address,ax
mov ax,seg p3
mov word ptr jmp_address+2,ax
call dword ptr [jmp_address]
mov ax,offset p2
mov word ptr jmp_address,ax
mov ax,seg p2
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
sub bx,2
mov si,1
call dword ptr [bx+si+1]
mov ax,offset p3
mov word ptr jmp_address,ax
mov ax,seg p3
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
sub bx,257
mov si,1
call dword ptr [bx+si+256]
mov ax,offset p2
mov word ptr jmp_address,ax
mov ax,seg p2
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
sub bx,2
mov di,1
call dword ptr [bx+di+1]
mov ax,offset p3
mov word ptr jmp_address,ax
mov ax,seg p3
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
sub bx,257
mov di,1
call dword ptr [bx+di+256]
mov ax,offset p2
mov word ptr jmp_address,ax
mov ax,seg p2
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
sub bx,2
call dword ptr [bx+2]
mov ax,offset p3
mov word ptr jmp_address,ax
mov ax,seg p3
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
sub bx,257
call dword ptr [bx+257]
mov ax,offset p2
mov word ptr jmp_address,ax
mov ax,seg p2
mov word ptr jmp_address+2,ax
mov si,offset jmp_address
sub si,2
call dword ptr [si+2]
mov ax,offset p3
mov word ptr jmp_address,ax
mov ax,seg p3
mov word ptr jmp_address+2,ax
mov si,offset jmp_address
sub si,257
call dword ptr [si+257]
mov ax,offset p2
mov word ptr jmp_address,ax
mov ax,seg p2
mov word ptr jmp_address+2,ax
mov di,offset jmp_address
sub di,2
call dword ptr [di+2]
mov ax,offset p3
mov word ptr jmp_address,ax
mov ax,seg p3
mov word ptr jmp_address+2,ax
mov di,offset jmp_address
sub di,257
call dword ptr [di+257]
mov ax,offset p2
mov word ptr jmp_address,ax
mov ax,seg p2
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
sub bx,2
mov si,2
call dword ptr [bx+si]
mov ax,offset p3
mov word ptr jmp_address,ax
mov ax,seg p3
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
call dword ptr [bx]
mov ax,offset p2
mov word ptr jmp_address,ax
mov ax,seg p2
mov word ptr jmp_address+2,ax
mov bx,offset jmp_address
sub bx,2
mov di,2
call dword ptr [bx+di]
mov ax,offset p3
mov word ptr jmp_address,ax
mov ax,seg p3
mov word ptr jmp_address+2,ax
mov si,offset jmp_address
call dword ptr [si]
mov ax,offset p2
mov word ptr jmp_address,ax
mov ax,seg p2
mov word ptr jmp_address+2,ax
mov di,offset jmp_address
call dword ptr [di]
mov ax,4c00h
int 21h
.DATA
message db 13,10,"Hello from PRTEST.",13,10,'$'
p2message db 13,10,"Hello from PTEST2.",13,10,'$'
p3message db 13,10,"Hello from PTEST3.",13,10,'$'
jmp_address dd 0
END start
PTEST2.ASM
.MODEL large
.DATA
EXTRN p2message:FAR
.CODE
PUBLIC p2
p2 PROC
mov dx,offset p2message
mov ah,9
int 21h
ret
p2 ENDP
END
PTEST3.ASM
.MODEL large
.DATA
EXTRN p3message:FAR
.CODE
PUBLIC p3
p3 PROC
mov dx,offset p3message
mov ah,9
int 21h
ret
p3 ENDP
END
QBNEST.BAS
common shared b
print:print "in main";
b=1
for i=0 to 1
print:print "Value of b variable is "b;
call nest1(i)
next
print:print fre(""),fre(0),fre(-1),fre(-2)
Directory of PC-SIG Library Disk #1933
Volume in drive A is OVL
Directory of A:\
OVL312 ARC 127888 5-10-89 12:43a
FILE1933 TXT 2591 12-28-89 3:08p
GO BAT 38 1-01-80 1:37a
GO TXT 540 1-01-80 1:05a
4 file(s) 131057 bytes
229376 bytes free
