DOS ain't dead - Possible CWSDPMI design flaw

Possible CWSDPMI design flaw (Developers)

posted by Japheth , Germany (South), 19.10.2010, 17:59

> However, the cause of the problem is found.

That was only half of the truth. The workaround has been implemented in DEBUGX - it's simply avoiding to call DPMI "save/restore state" when the state size is zero. However, this fixes only 50%, DEBUGX on CWSDPMI is now able to temporarily switch to real-mode and back with raw switches, but the other direction ( RM -> PM -> RM ) still won't work.

CWSDPMI's state size of zero made me suspicious already, and a quick look into its source - DPMISIM.ASM - revealed that the raw switches are only supposed to work if the first switch is initiated from protected-mode. Trying to do it the other way - as DEBUGX may do - will cause a freeze.

---
MS-DOS forever!

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Complete thread:

With DPMI into protect mode and back - Laaca, 13.08.2010, 10:36
- With DPMI into protect mode and back - EDIT: example - ecm, 13.08.2010, 14:30
  - With DPMI into protect mode and back - EDIT: example - DOS386, 26.08.2010, 09:18
    - With DPMI into protect mode and back - EDIT: example - ecm, 26.08.2010, 14:35
      - With DPMI into protect mode and back - EDIT: example - DOS386, 27.08.2010, 03:33
        With DPMI into protect mode and back - EDIT: example - ecm, 30.08.2010, 21:51
        With DPMI into protect mode and back | physical memory - DOS386, 06.09.2010, 20:08
        With DPMI into protect mode and back | physical memory - ecm, 07.09.2010, 17:04
        With DPMI into protect mode and back | physical memory - DOS386, 08.09.2010, 00:51
        With DPMI into protect mode and back | physical memory - ecm, 08.09.2010, 20:53
        With DPMI into protect mode and back | physical memory - DOS386, 11.09.2010, 01:02
        With DPMI into protect mode and back | physical memory - ecm, 11.09.2010, 01:25
- With DPMI into protect mode and back - Japheth, 18.08.2010, 08:04
  - With DPMI into protect mode and back - Japheth, 18.10.2010, 11:17
    - With DPMI into protect mode and back - Rugxulo, 18.10.2010, 23:07
      - With DPMI into protect mode and back - Japheth, 19.10.2010, 09:58
        With DPMI into protect mode and back - Rugxulo, 19.10.2010, 10:09
        With DPMI into protect mode and back - Japheth, 19.10.2010, 10:20
        Possible CWSDPMI design flaw - Japheth, 19.10.2010, 17:59