DOS ain't dead

debugxv - how to use I/O watchpoint? (Users)

posted by Japheth , Germany (South), 12.04.2025, 16:58

> Now I'd like to know how to patch (skip) this IO access at runtime by some
> TSR or loader as I cannot patch the EXE coz it's encrypted or packed by
> unknown exe packer... Speedsys checks for V86 mode and complains about it
> (can run but very limitest tests available)

That's tricky in real-mode. You could perhaps use normal "execute" hw breakpoints? You have to find out the offset of the "OUT 22,al" instruction (relative to PSP:0), and a TSR might then set such a bp before the program starts. When the bp is triggered, to be safe, checking the 2 bytes at CS:IP might be a good idea...

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MS-DOS forever!

Complete thread:

• debugxv - how to use I/O watchpoint? - RayeR, 08.04.2025, 10:44 (Users)
  • debugxv - how to use I/O watchpoint? - Japheth, 08.04.2025, 12:30
    • debugxv - how to use I/O watchpoint? - RayeR, 08.04.2025, 14:11
      • debugxv - how to use I/O watchpoint? - Japheth, 09.04.2025, 05:53
        • debugxv - how to use I/O watchpoint? - RayeR, 09.04.2025, 11:19
          • debugxv - how to use I/O watchpoint? - Japheth, 09.04.2025, 16:33
            • debugxv - how to use I/O watchpoint? - RayeR, 09.04.2025, 20:08
            • debugxv - how to use I/O watchpoint? - RayeR, 11.04.2025, 06:14
              • debugxv - how to use I/O watchpoint? - Japheth, 11.04.2025, 09:10
                • debugxv - how to use I/O watchpoint? - RayeR, 12.04.2025, 05:59
                  • debugxv - how to use I/O watchpoint? - Japheth, 12.04.2025, 09:16
                    • debugxv - how to use I/O watchpoint? - RayeR, 12.04.2025, 15:02
                  • debugxv - how to use I/O watchpoint? - Japheth, 12.04.2025, 16:58
                  • debugxv - how to use I/O watchpoint? - rr, 12.04.2025, 18:10
                    • debugxv - how to use I/O watchpoint? - rr, 12.04.2025, 19:05
                      • debugxv - how to use I/O watchpoint? - rr, 12.04.2025, 20:11
                    • debugxv - how to use I/O watchpoint? - RayeR, 13.04.2025, 07:12
                      • debugxv - how to use I/O watchpoint? - ecm, 13.04.2025, 14:13
                        • speedsys.exe packed - ecm, 13.04.2025, 14:25
                          • speedsys.exe packed - ecm, 13.04.2025, 14:32
                            • speedsys.exe packed - RayeR, 15.04.2025, 06:43
        • debugxv - how to use I/O watchpoint? - tom, 09.04.2025, 21:06
          • debugxv - how to use I/O watchpoint? - Japheth, 10.04.2025, 13:14
            • debugxv - how to use I/O watchpoint? - tom, 10.04.2025, 18:27
    • debugxv - how to use I/O watchpoint? - RayeR, 09.04.2025, 02:58
      • debugxv - how to use I/O watchpoint? - Japheth, 09.04.2025, 05:50