Questions tagged [dos]

Disc Operating System, started as 16-bit OS for PC-AT/XT x86++ platforms

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40 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 ...
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1answer
49 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 ...
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1answer
29 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 ...
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0answers
100 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 ...
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1answer
70 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
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1answer
68 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. ...
2
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1answer
169 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
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1answer
157 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
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3answers
668 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 ...
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2answers
160 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 ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦...
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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 ...
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1answer
620 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 ...
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2answers
408 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
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0answers
260 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
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1answer
615 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 ...
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1answer
309 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
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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? ...
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2answers
186 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
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0answers
861 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
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2answers
170 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
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1answer
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: ...
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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
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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 ...
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1answer
1k 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
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1answer
941 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
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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 ...
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1answer
1k 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
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4answers
968 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
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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
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1answer
2k views

DOS program debug in IDA?

Does anybody know something hack to debug 16bit DOS program in IDA 6.1?
2
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3answers
853 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 ...