Feature request: Make ComLoader and ExeLoader use a future DOS INT21H EXEC function.

[maximilien-noal]

Since both will create a PSP, etc...

[maximilien-noal]

https://github.com/segin/readexe for an example of code that knows how to differentiate between EXE/COM and other variants.

[matthewturk]

Is this the same as implementing INT 21h 0x4B? I'm trying to reverse a program that is initialized by a COM file (which loads up some interrupt handlers etc), then it swaps between two different EXE-format files via 0x4B. Is this something that might be feasible for a new contributor to take a look at, or maybe too hard?

[maximilien-noal]

This is indeed related to function 0x41b. This is also related to DOS process management.

In essence, the comloader and exeloader would be replaced by this process:

• mount the virtual drive. We already do that.
• launch the DOS kernel
• call 0x41b to load and exec the file, giving it the path and program arguments
• this call determines if it's a com or exe file, creates the new PSP inside the SDA, takes care of existing PSPs, and eventually runs the program.

The 'load but don't exec' mode of this function can be skipped if your program doesn't use this mode. This mode is related to TSR support.

This depends on three DOS data structures:

• The SDA. We don't have that at the moment.
• The PSP. We set it up manually in either the comloader or exeloader. Both should be instead a new class based on MemoryBasedDataStructure instead.

The SDA should host the PSP chain.

I think it is doable, now that every dependency between services and classes are resolved at compile time in Spice86DependencyInjection.cs

The book 'undocumented DOS' is a great resource about this.

We have a discord if you need guidance. I will be glad to help.
https://discord.gg/h99HFjZX