Category : Miscellaneous Language Source Code
Archive   : EX2CM104.ZIP
Filename : EXE2COM.DOC

EXE2COM 1.04
By Chris Dunford/Cove Software

| indicates information changed/added in recent versions.

Purpose
-------
EXE2COM is a one-for-one replacement for the EXE2BIN program
that was formerly distributed with DOS. Beginning with DOS 3.3,
EXE2BIN has been moved to the disk that comes with the DOS
Technical Reference and thus is not available without extra
cost.


Usage
-----
Usage is identical to DOS's EXE2BIN except that the output file
extension defaults to COM rather than BIN, and there is an
optional switch that displays EXE file information rather than
converting the file to COM.

Complete usage is:

EXE2COM [/I] [d:][path]file[ext] [d:][path][file][ext]

The drive and path of the first file default to the current
drive and path, if not specified. The extension of the first
file defaults to EXE, if not specified.

If the second file is completely unspecified, it defaults to the
same drive, path, and filename as the first, except that the
extension will be COM.

If the second file is specified but without an extension, COM
will be assumed (this is different from EXE2BIN).

| If /I is specified, information about the EXE file is displayed
| and no conversion is performed. The output file name, if
| specified, is ignored.

The simplest (and usual) usage is simply:

EXE2COM file

which will take the named EXE file in the current directory and
convert it to a COM file in the same directory.


Operation
---------
EXE2COM runs the same way as EXE2BIN, with the following
exceptions:

1. The binary fixup option of EXE2BIN (IP=0, segment fixups
required) is not supported.

2. The EXE file checksum is not verified.

3. Error messages are more useful, and a warning is provided
if a COM file is created with an initial IP other than 100H.

4. The default output file extension is COM rather than BIN.


| Information display
| -------------------
| If you use the /I switch, EXE2COM just displays information
| about the EXE file and does not attempt to convert it to COM
| (therefore, the EXE file need not be a convertible file). Here
| is a typical display, resulting from running EXE2COM on itself
| (version 1.04) with the /I switch:
|
| exe2com.exe (hex) (dec)
| EXE file size 396B 14699
| EXE header size (para) 20 32
| Program image size (bytes) 376B 14187
| Minimum load size (bytes) 8CDB 36059
| Min allocation (para) 557 1367
| Max allocation (para) FFFF 65535
| * Initial CS:IP 0000:072C
| * Initial SS:SP 084D:0800 2048 (stack size)
| * Relocation count 4 4
| Relo table start 001E 30
| EXE file checksum 411D 16669
| Overlay number 0 0
| * = this item prevents conversion to BIN/COM
|
| The fields that may need some explanation:
|
| Program image size: this is the size of the program itself
| (i.e., the size of the EXE file less the size of the header
| information). This much memory is required to load a copy of
| the program's code and pre-allocated data.
|
| Minimum load size: at least this much free memory is required in
| order to run the program.
|
| Min/max allocation: the minimum/maximum number of 16-byte
| paragraphs that will be needed above the end of the program
| image when it is loaded. Minimum load size is the sum of the
| program image size and the minimum allocation.
|
| If an item is starred (*), this prevents the EXE file from being
| converted to a COM file.


Error Messages
--------------
These are EXE2COM's error messages. If one of these is seen,
the EXE file will not be converted and the errorlevel returned
by EXE2COM will be 1.

ERROR READING EXE HEADER
EXE2COM was unable to read the EXE file header from disk.

ERROR WRITING OUTPUT FILE
EXE2COM was unable to write the converted file to disk.

INVALID EXE FILE SIGNATURE
The first two bytes of an EXE file should be ASCII 'M' and
'Z'. This was not the case, and it's probably not an EXE
file.

EXE HAS RELOCATABLE ITEMS
In order to be converted to a COM file, an EXE file cannot
have any direct references to segments. For example, the
assembler instruction "mov ax,code" (where CODE is a segment
name) is a segment reference. One or more segment
references were found in the EXE file.

EXE HAS STACK SEGMENT
In order to be converted to a COM file, an EXE file cannot
have a stack segment.

EXE HAS NONZERO CS
In order to be converted to a COM file, an EXE file must
have a code segment that begins at offset 0 of the code
image in the EXE file.

IP NOT 0 OR 100H
In order to be converted to a binary file, an EXE file must
have an entry point of 0 or 100H within the code segment.
For COM files, the entry point should be 100H. For SYS
files (device drivers), the entry point should be 0.

PROGRAM EXCEEDS 64K
In order to be converted to a binary file, the total size of
the code to be loaded (including the PSP) must not exceed
64K bytes.

UNKNOWN ERROR
Internal error. Notify the author.


Warning message
---------------
EXE2COM has one warning message:

COM FILE, INITIAL IP NOT 100H

The entry point of all COM files should be 100H. If you are
creating a COM file an the entry point is not 100H, EXE2COM will
do the job but let you know that there is a potential problem.


Source
------
Source code should be included with this archive. Users are
encouraged to modify, improve, and/or correct the source for
EXE2COM and submit the new program to the author for
distribution. Please identify clearly any changes made and
stick with portable code (no inline assembler, PLEASE).

Source for EXE2COM was written for the Microsoft C compiler
(v.5.0) but will also compile correctly with Borland's Turbo C
(v.1.5). It should be easily portable to most other compilers.


Public domain
-------------
EXE2COM is hereby donated by the author to the public domain.


History
-------
Version 1.00 04/17/87: Original version by
Christopher J. Dunford
The Cove Software Group
PO Box 1072
Columbia, MD 21044
(301) 992-9371
CompuServe 76703,2002

Version 1.01: port to Turbo C by
Roger Schlafly
Borland International
Scotts Valley, CA 95066
CompuServe 76067,511

Version 1.02 11/22/87: bug fix for even 512-byte file made to
Turbo C port by
Chris Blum ( Consultant )
509 West Main, Front
Ashland, Ohio 44805
CompuServe 76625,1041

Chris Dunford duplicated the fix in the C86 source.

Version 1.03 12/30/87: by Chris Dunford
Ported to Microsoft C 5.0. This is now the "official"
version.

Increased size of I/O buffer to 4K for speed reasons.
EXE2COM 1.03 is twice as fast as 1.02 and slightly
faster than EXE2BIN.

Version 1.04 03/08/88: by Chris Dunford
Cleaned up some old code from the original quickie.

Source should now compile under either MSC or TC.

Added /I switch.

In earlier versions, we defined an error code for nonzero
CS, but didn't actually check; now we do.