"An unhandled exception occured" running a DOS game

[sardaukar]

Describe the bug
I tried to run Spice86 -e <path/to>/ROE2MAIN.EXE to run the main executable for Rules of Engagement II and it immediately shows an error - does that mean it's not a real-mode DOS binary?

To Reproduce
Steps to reproduce the behavior:

1. Run Spice86 -e <path/to>/ROE2MAIN.EXE
2. See error message that says:

{"TargetSite":"Void Grp5()","Message":"An error occurred while machine was in this state: Cycles=6770 CS:IP=0x1:0xEE2/0xEF2 EAX=0x7F06 EBX=0x5 ECX=0xE50 EDX=0x0 ESI=0x0 EDI=0x0 EBP=0xD9A8 ESP=0xD978 SS=0x0 DS=0xA ES=0xA FS=0x0 GS=0x0 flags=0x7016 (      AP ).\nError is: Invalid group index 0x7","StackTrace":"   at Spice86.Core.Emulator.CPU.InstructionsImpl.Instructions16Or32.Grp5() in /home/sardaukar/Code/FOREIGN/Spice86/src/Spice86.Core/Emulator/CPU/InstructionsImpl/Instructions16Or32.cs:line 96\n   at Spice86.Core.Emulator.CPU.Cpu.ExecOpcode(Byte opcode) in /home/sardaukar/Code/FOREIGN/Spice86/src/Spice86.Core/Emulator/CPU/CPU.cs:line 1076\n   at Spice86.Core.Emulator.CPU.Cpu.ExecuteNext() in /home/sardaukar/Code/FOREIGN/Spice86/src/Spice86.Core/Emulator/CPU/CPU.cs:line 127\n   at Spice86.Core.Emulator.VM.EmulationLoop.RunLoop() in /home/sardaukar/Code/FOREIGN/Spice86/src/Spice86.Core/Emulator/VM/EmulationLoop.cs:line 103\n   at Spice86.Core.Emulator.VM.EmulationLoop.StartRunLoop(FunctionHandler functionHandler) in /home/sardaukar/Code/FOREIGN/Spice86/src/Spice86.Core/Emulator/VM/EmulationLoop.cs:line 92\n   at Spice86.Core.Emulator.VM.EmulationLoop.Run() in /home/sardaukar/Code/FOREIGN/Spice86/src/Spice86.Core/Emulator/VM/EmulationLoop.cs:line 68\n   at Spice86.Core.Emulator.ProgramExecutor.Run() in /home/sardaukar/Code/FOREIGN/Spice86/src/Spice86.Core/Emulator/ProgramExecutor.cs:line 108\n   at Spice86.ViewModels.MainWindowViewModel.EmulatorThread() in /home/sardaukar/Code/FOREIGN/Spice86/src/Spice86/ViewModels/MainWindowViewModel.cs:line 387"}

Expected behavior
Game should start...?

Screenshots

Desktop (please complete the following information):

• OS: EndeavourOS (Linux)
• Version: rolling releases, doesn't have a version

Additional context
Is this not supported in Linux? I can try Windows too

[maximilien-noal]

Hello,

Thank you for your interest in Spice86.

First of all, this game looks COOL ! I wasn't aware at all of it. I'd love to help you make it run.

Is Linux supported ?

Yes, it is! .NET and Avalonia are fully cross platform.

Moreover VSCode + C# Dev Kit extension, or JetBrains Rider (which is free) are fine as a .NET dev platform on Linux, assuming the SDK has been installed.

I use JetBrains Rider daily: https://www.jetbrains.com/rider/download/

How to detect a protected mode game ?

Run it with dosbox staging. If staging switches to more than 3000 cycles/ms, it's a protected mode game.

It also usually has a DPMI server, such as DOS4GW.EXE inside its directory.

Then why the game doesn't work ?

That's an issue somewhere in the emulation side of things.

For example the PIT class was recently fixed, and it fixed the sound being way too fast in Monkey Island.

You should probably re-run the game with the -l parameter to get heavy logs, and attach them to this issue.

The -f argument is also interesting, in that it will make Spice86 throw an error if an unemulated port is found.

Logs are stored in the logs folder, right besides the spice86 binary.

I'd recommand to use the DOSBox Staging Debugger and Spice86 Debugger side by side and spot the issue in the dissassembly view. I wonder where the two emulators start to diverge ?

Also perhaps it needs EMS. Try enabling it with --Ems

[maximilien-noal]

The game doesn't use

• several executables (we don't support that at the moment)
• XMS (it can use it, but it's not required)
• protected mode

So it's really a bug that it doesn't work.

The good news is, it's probably not a lot to fix.

[sardaukar]

@maximilien-noal do you have docs for contributors? I'd be interested in helping - as you said, this game looks cool :)

[maximilien-noal]

@sardaukar

Here it is :

https://github.com/OpenRakis/Spice86/blob/master/CONTRIBUTING.md

One caveat : PR can be fine even if the github CI fails. the Windows CI fails to run sometimes for some reason.

[sardaukar]

This may be way over my head, but I'll give it a shot 😃

[sardaukar]

OK, so to figure out what's failing, I tried to output the opcodes as they're executed:

if (_loggerService.IsEnabled(LogEventLevel.Debug)) {
  _loggerService.Debug("Opcode to run: {opcode}", opcode.ToString("x2"));
}

And it's an 0xff so by this opcode table it should be a GRP5 and the index is read with ModRM.read to get the group index, but the group is set to 7, which does not exist... 🤔

What other (more accurate) emulator do you use to get a comparison, cycle by cycle?

[maximilien-noal]

I think the game is confused earlier on and eventually tries to execute data as code.

I'd compare cycle by cycle with the dosbox staging debugger, with core=normal so you avoid the DOSBox JIT.

[maximilien-noal]

Here are some logs. Command line arguments:

-f -l -e "C:\Program Files (x86)\GOG Galaxy\Games\Rules of Engagement II\ROE2MAIN.EXE" --Ems

log-20250405.txt

Sounds like the DosInt21Handler class handles a call incorrectly.

[sardaukar]

yep, it looks like it's jumping to a wrong place and it's interpreting it as code