DOS ain't dead

Can a DPMI program enter V86M with iretd instruction? (DOSX)

posted by alexfru, USA, 21.01.2023, 03:35

> I played around with lDebugX and the dpmimini example in my local Linux
> box's dosemu2, and found that an iretd (or o32
> iret) which sets the
> VM flag apparently tries to load a stack pointer from the PM stack, I
> get a Stack fault if this cannot succeed. In case it does succeed, the DPMI
> host apparently returns a General protection fault.
>
> Is it possible to enter V86M using just iretd in DPMI
> protected mode? If yes: How much does the DPMI host get confused by this,
> and can it avoid that?

If you run CWSDPMI in ring 0, you should definitely be able to IRET into virtual 8086 mode. But then you'll also need to prepare things to go back.

Also, real-mode code may be executed in virtual 8086 mode.

What are you trying to achieve?

Complete thread:

• Can a DPMI program enter V86M with iretd instruction? - ecm, 20.01.2023, 17:52
  • Can a DPMI program enter V86M with iretd instruction? - alexfru, 21.01.2023, 03:35
    • Can a DPMI program enter V86M with iretd instruction? - ecm, 21.01.2023, 09:03
      • Can a DPMI program enter V86M with iretd instruction? - alexfru, 21.01.2023, 09:50
      • Can a DPMI program enter V86M with iretd instruction? - tkchia, 21.01.2023, 14:06
        • Can a DPMI program enter V86M with iretd instruction? - alexfru, 21.01.2023, 17:13