Questions tagged [dos]

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

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4
votes
3answers
265 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
149 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
346 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 ...
8
votes
2answers
250 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
207 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
465 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 ...
0
votes
1answer
231 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 ...
1
vote
0answers
66 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
169 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
695 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
136 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 ...
3
votes
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: ...
2
votes
1answer
1k 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
888 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
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 ...
2
votes
1answer
821 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
839 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.
4
votes
4answers
827 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
4k 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
2k views

DOS program debug in IDA?

Does anybody know something hack to debug 16bit DOS program in IDA 6.1?
2
votes
3answers
770 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 ...