Reverse Engineering with DOSBox debug build

nospam@example.com (Sylvester Rac) — Sat, 04 Nov 2023 23:43:00 +0000

DosBox comes with it's own built-in debugger, which can be useful when reversing old DOS games.

This feature needs to be enabled at build time (--enable-debug or --enable-debug=heavy), so either download the special binary or build it from source. I went through the build process in a previous post: https://blog.aupcgroup.com/index.php?/archives/32-Hacking-a-DOS-32-bit-protected-mode-game-from-1997.html

This gives a nice view with registers, dissassembly and memory views:

This VOGONS thread has a quick summary on the DosBox built-in debugger: https://www.vogons.org/viewtopic.php?t=3944

Mount a Bochs disk image

nospam@example.com (Sylvester Rac) — Sat, 18 Apr 2020 04:58:00 +0000

We can mount a bochs disk image from Linx with the following command:

sudo mount -t msdos -o loop,offset=32256 disk.img /mnt/bochs/

The offset of 32256 is correct if the image was created with the Bochs Disk Image Creator, but how can the offset be calculated?