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Reconstructed source code for the Microprose game F-15 Strike Eagle 2 for MS-DOS

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F-15 Strike Eagle 2 source code reconstruction

This is a work in progress project to reconstruct the source code for the MS-DOS version of the Microprose game F-15 Strike Eagle 2 v451.03 (the definitive 1991 Desert Storm expansion disk version).

The original game was written in a mixture of C and assembly. The C source code was compiled with the Microsoft C compiler v5.1.

The reconstruction aims to be bug-for-bug faithful, and the C routines yield code that's identical to the original at the CPU instruction level (when compiled with the same compiler with appropriate flags), while allowing for layout differences in the executable.

Given the fact that this game shares a lot of DNA with the game that preceeded it (F-19) and the one that came after (F-117), there is probably a lot of overlap, and this effort might lead to supporting those games in the future.

This is just the reconstruction project, porting to a modern OS and potential improvements and bugfixes will be carried out under a separate project in the future.

This repository contains no game assets, executables or other copyrighted material, it's a clean rewrite of the game's source code based on my analysis of the game binaries obtained from the original floppy disks, for preservation and historical research purposes, and as such should fall under the interoperability exemption of the DMCA.

Development journal: https://neuviemeporte.github.io/category/f15-se2

Executables

The game consists of multiple executables, some of which are the target of source code reconstruction:

  • f15.com - the game loader, originally written in obfuscated, self-modifying assembly code which included disk-based copy protection.
  • su.exe - the setup executable, lets player pick the video and sound hardware they want to use and does some initialization work
  • start.exe - the first stage of the game, handles the intro, mission selection and briefing
  • egame.exe - the second stage of the game, the actual 3D flight engine
  • end.exe - the third stage of the game with the mission debriefing, loader goes back to start.exe afterwards
  • mgraphic.exe - the MCGA video driver overlay, dynamically loaded assembly routines for graphics handling

The remaining executables are ignored in this project, see the development journal for rationale.

Status

As of the time of writing this, the status of the reconstruction is as follows:

  • f15.com/su.exe - fully reconstructed into a minimal, functionally equivalent loader executable (f15.exe) that works as a drop-in replacement with the original game.
  • start.exe - most if not all C code has been reconstructed, but the executable is not yet runnable. The assembly routines need tweaking and porting into C before it can be considered complete.
  • egame.exe - not touched
  • end.exe - not touched
  • mgraphic.exe - overlay header and overall layout understood, some research done into the purpose of individual routines inside, but reconstruction not started yet.

The reconstruction is the first step, multiple variables and routines still have generic names because they are not fully understood, and will have to be further analyzed through instrumentation and experimentation.

Building

Prerequisites:

  • a copy of the MS C v5.1 compiler placed in the dos/msc510 directory
  • the dosbox emulator has been installed
  • relatively recent (3.8-ish) Python installed

Clone the project and run make inside. It will download and build the mzretools and UASM repositories as part of the build process.

Verification

The Makefile contains a target for automatically comparing the reconstruction with the original using the mzdiff tool, run make verify to perform the comparison and make sure any changes to the reconstructed source code did not make it divergent. This repo is a place to host a version of the game that is as close to the original as possible, so any contributions, while deeply welcome, need to make sure that consistency is not broken using this mechanism.

For reference, I'm using original binaries with the following MD5 sums to compare against:

  • start.exe: packed: 320bc386921add664e4c18e86c9d6f90 unpacked: cf6e997ed4582cf82db6ec37d2b1a6fd

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Reconstructed source code for the Microprose game F-15 Strike Eagle 2 for MS-DOS

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