Questions tagged [dos]
Disc Operating System, started as 16-bit OS for PC-AT/XT x86++ platforms
35
questions
1
vote
1answer
44 views
Finding API in ROM dump (DOS debug)
Have dumped the ROM from a HP 200LX using these instructions:
debug #Enters the debug mode
r bx #Reads the bx register and prompts you to enter a new value
30 #The new value for bx
r cx #Reads the cx ...
0
votes
0answers
180 views
Where to start analyzing a 16 bit dos program?
I've tried to analyze this small exe online.
I've tried with https://onlinedisassembler.com/odaweb/ (link) but it's hard for me to get the first question:
Why the tool doesn't try to detect the set ...
0
votes
1answer
45 views
Reverse engineering mode X VGA function(s)
I'm trying to reverse engineer an old DOS game. At the moment I'm stuck at a function that implements some functionality of VGA running in mode X. My issue is that any of the available sample codes on ...
2
votes
2answers
113 views
Finding Code Reference String in MS-DOS 16-bit Executable with IDA Pro
Have an application that has code to detect serial port model. I'm trying to work out how it works through static analysis. I have unpacked the EXE and can find the references to the strings:
dseg:...
0
votes
2answers
102 views
How to retrieve name of a variable defined in the data segment in IDA when no process is attached?
I have disassembled an old DOS application with IDA. It run in 16-bit real mode. Some instructions are referencing variables defined in the data segment (DS).
push word ptr ds:8401h
Since I have ...
2
votes
1answer
53 views
Why would VGA port 03CC respond with bit 3 set and bit 2 not?
I'm reverse-engineering some code I wrote in the middle-90s for which the source is long-lost and I'm a bit baffled by some VGA code I've encountered. I think it's probably from library or 3rd party ...
0
votes
1answer
36 views
How to determine commands sent over DC-37 port by software from 1992
Background
Since some time we've been in the possession of a greenhouse. It was build around 1990 and had an automated system for climate control. However most of the installation has been removed ...
1
vote
1answer
367 views
IDA/Hexrays: local variable allocation has failed; how to fix this?
I'm reverse engineering an old DOS game that's using the DOS/4GW extender. The game includes some libraries that I already successfully reversed in a different application, so I'm pretty sure that the ...
0
votes
1answer
120 views
Within A Folder of 100s of 16-bit MS-DOS Disassembled EXEs Identify Ones That Need/Use DOS/4GW
So far I batch disassembled all files using following PowerShell and IDA:
$files = Get-Content S:\files.txt
ForEach ($file in $files)
{
Write-Host "Processing $file"
&"C:\Program Files\...
3
votes
1answer
71 views
x86 disassembly confusion regarding VESA functions
I'm trying to disassemble an old DOS application and got stuck at some point of the VESA graphics handling.
The VESA function to be called will be stored in a global variable, e.g. ...
3
votes
2answers
433 views
Trying to view sprites from an old game
I am looking to decompile the sprite data from an old DOS Game (Treasure Cove). If it helps any, I found that the game was written with the Borland C++ Programming Language.
It appears that the ...
0
votes
1answer
333 views
Converting 2 bytes into date
I am trying to convert the following bytes into their corresponding dates.
I am not 100% on format the dates is stored, this format is returned from the application that read them.
Bytes Date ...
6
votes
3answers
2k views
Reverse Engineering (very) old DOS calculation program
I have recently joined a company that is specialized in air ducts & ventilation systems and I was quite surprised when I noticed that they are still using a DOS program to calculate the pressure ...
1
vote
2answers
166 views
Assembly that just seems to be a jumble
I've disassembled an old DOS program into assembly and I'm trying to figure out a function call. Here is the ASM:
seg000:373C ; ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ S U B R O U T I N E ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦...
7
votes
2answers
1k views
What's this assembly doing?
I have been trying to figure out the assembly for part of a DOS game and there is an operation that keeps getting called that uses all 4 registers. I can see what each line does but I can't for the ...
1
vote
1answer
855 views
Working with 16bit offsets and segments in Radare2
I have a simple DOS COM program which I want to analyse using Radare2:
USE16
ORG 100h
mov ax, cs
dec ax
mov ds, ax
mov dx, message+10h
mov ah, 9
int 21h
ret
message: db "Hello ...
9
votes
2answers
530 views
How did this 80286 detection code work?
I'm poking through a disassembled 16-bit DOS game circa 1992. The original system requirements state that the game needs an IBM AT-compatible machine or later, with the 286 processor, to run. And ...
2
votes
0answers
295 views
BasicCompiler: wanted binaries which BC.exe or QB.exe (compiler) generates
I was in charge of analyze and reverse engineering the old unknown EXE for past few month. The binary works on MS-DOS for NEC-PC98 (retro PC), old (20years more ago), nobody knows how it's made.
I ...
3
votes
1answer
674 views
debugging a graphical msdos game
There is a DOS game I want to run through a debugger. I tried using (FreeDos)
DEBUG.COM over DosBox. But the problem is that this game uses graphics, and this messes up the output of DEBUG.COM.
Is ...
2
votes
1answer
405 views
DOS Executable Segments
In a DOS EXE file, if I have sub1, sub2, and sub3, split between two code segments, how do I know which sub is in which segment? There seem to be no physical markers in the exe code.
I know the EXE ...
2
votes
0answers
89 views
COBOLII-MB 2.xx
I have a really old cobol program that was used to store some data, the company is no loger active and the program had to receive a key every 3 months. What tools I can use to reverse a cobol program? ...
0
votes
2answers
195 views
Issues rewriting portions of DOS app's assembly
I am working on editing an old DOS program's assembly, but I'm running into some odd issues.
I'm using IDA Pro 6.4 and a hex editor to patch. I'm code-caving the new data by removing old stuff never ...
3
votes
0answers
966 views
Reverse-engineering DOS game's data files
I would like to figure out the data format used by an old DOS game I used to play when I was a kid. That link includes a full download for all the files and it runs fine in DOSBox if you want to try ...
2
votes
2answers
194 views
LE executable Fixup Record Table format
So I have started reverse engineering an old LE executable. So to get a better understanding of the format. I started by writing a parser for this format. Using the following resources I have made ...
4
votes
2answers
2k views
Is there a way to import debug/symbol information of a C++ DOS executable to IDA?
I have an old DOS program compiled using Borland C++ (1991 version)
The end of the executable contains many strings preceded by an underscore which looks like debug/symbol information :
eg: ...
2
votes
1answer
2k views
IDA Pro and recognized library functions
I start by saying that I'm completely new to the topic of reversing although I have many years of experience with programming in general.
I've some problems with automatic recognition of library ...
2
votes
2answers
1k views
Unrecognized procedures in IDA Pro
for hobby I'm just trying to reverse and old DOS game executable.
I'm quite new with reversing so I'm having hard time understanding some bits about IDA Pro. I let the program choose the best-fit ...
1
vote
1answer
2k views
DOS interrupt problem with int 21h 0ah
I have this assembly code that reads a string of 120 bytes. If I try to fill the buffer by pressing a key until it stops writing, the enter key doesn't work. I counted the characters and I found that ...
3
votes
1answer
1k views
Debugging a DOS4GW/Causeway packed program
I have a DOS program that I'm trying to reverse engineer. It uses the Causeway Extender(also known as DOS4GW) in order to load the program into 32-bit protected mode, and IDA Pro 5.0 cannot extract ...
12
votes
2answers
2k views
How can I find the source of a string in an old DOS game?
I am attempting to amend some strings in an old DOS game (FIFA International Soccer), specifically the names of players.
In the past it hasn't been too hard to pull off such a task on post-DOS games ...
1
vote
1answer
2k views
Change a text in DOS executables [closed]
We have a DOS executable program like to NC. How do we find and change a text or a ASCII art in it?
I'm a newbie in reverse.
5
votes
4answers
1k views
Any correlation between DOS Program Segment Prefix and the base address of loaded executable?
I'm using IDA to disassemble Test Drive III. It's a 1990 DOS game. The *.EXE has MZ format.
The game uses a number of anti-reversing features such as copying its code to segment (PSPseg+2be7) where ...
4
votes
1answer
5k views
How to start a DOS application in DOSbox in debug mode?
DOSbox compiled with --enable-debug=heavy option becomes a powerful reversing tool. Anytime I feel like checking the disassembly and memory state I just hit Alt+Pause.
But, what if I want to see the ...
5
votes
1answer
3k views
2
votes
3answers
922 views
Interrupt interception
I'm currently reading 40hex magazine regarding virus writing in the early 90's. They talk a lot there about interrupt intercepting Which is something security guys from anti viruses company will try ...
