A few months ago I started tinkering with an old DOS-based game trying to figure out its internal data structure. Progress was good in the beginning, and I was quickly able to alter the saved game to give myself some advantages.
Long story short, after a while I needed to figure out how the game handled a particular part of the savegame, since I couldn’t figure it out using a hex editor. But since the game was using a DOS extender, also known as DOS/4GW, loading it directly into Ida Pro Free wouldn’t help. It only gave meaningless garbage in return.
I found the open source DOS extender DOS/32. This has a utility known as SUNSYS Bind Utility which can be used to “Unbind and discard existing Extender/Stub from LE/LX/LC executable” as it says in the documentation.
Place the utility, along with the executable in question, in the same directory and fire up Dosbox (or the real thing) and enter the following command.
SB /U filename.exe
This will produce a unbinded file which can be loaded directly into Ida Pro Free. In my case I ended up with a file ending in .LE, which stands for “Linear Executable”.
Hopefully this can help others who want to peak into old DOS games.