DOS ain't dead - VESAMTTR (recovered from Google)

VESAMTTR (recovered from Google) (DOSX)

posted by Japheth , Germany (South), 06.09.2007, 08:27

> BTW I tried to play with code under WinXP VDM. I can read GDTR and LDTR, I
> can allocate LDT descriptor, I can set descriptor's base and limit along
> GDTR values, but when I try to read some data (movedata or farpeekb) via
> selector of this descriptor it crashes. How does NT protect reading of
> GDT? My code has PL=3 and my LDT decriptor I'm acessing has also DLP=3 so
> this should be OK. Is it some paging magic here? Or does CPU have some
> flag to protect GDT against all PL>0 code?

on NT the pages which contain GDT, IDT, LDT and paging tables are protected ("system" PTEs). IIRC some versions of NT/XP additionally don't allow descriptor limits > 7FFFFFFFh (which caused some troubles for older versions of DJGPP).

---
MS-DOS forever!

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Complete thread:

VESAMTTR (recovered from Google) - DOS386, 23.07.2007, 02:42 (DOSX)
- VESAMTTR (recovered from Google) - RayeR, 03.09.2007, 20:45
- VESAMTTR (recovered from Google) - RayeR, 03.09.2007, 20:58
  - VESAMTTR (recovered from Google) - Rugxulo, 04.09.2007, 02:01
    - VESAMTTR (recovered from Google) - RayeR, 04.09.2007, 12:59
      - VESAMTTR (recovered from Google) - Japheth, 04.09.2007, 16:41
        VESAMTTR (recovered from Google) - RayeR, 04.09.2007, 20:25
        VESAMTTR (recovered from Google) - Japheth, 04.09.2007, 22:32
        VESAMTTR (recovered from Google) - DOS386, 05.09.2007, 02:17
        VESAMTTR (recovered from Google) - RayeR, 05.09.2007, 09:53
        VESAMTTR (recovered from Google) - Japheth, 06.09.2007, 08:27
        VESAMTTR (recovered from Google) - DOS386, 11.09.2007, 06:54
        VESAMTTR (recovered from Google) - RayeR, 12.09.2007, 20:31
        VESAMTTR (recovered from Google) - DOS386, 13.09.2007, 02:21
      - VESAMTTR (recovered from Google) - Rugxulo, 05.09.2007, 14:51
        VESAMTTR (recovered from Google) - RayeR, 05.09.2007, 16:22
        VESAMTTR (recovered from Google) - Rugxulo, 05.09.2007, 20:56
        VESAMTTR (recovered from Google) - RayeR, 06.09.2007, 01:08
        VESAMTTR (recovered from Google) - Rugxulo, 06.09.2007, 04:40
        VESAMTTR (recovered from Google) - rr, 06.09.2007, 16:56
        VESAMTTR (recovered from Google) - Rugxulo, 07.09.2007, 04:12
        VESAMTTR (recovered from Google) - RayeR, 06.09.2007, 22:35
        VESAMTTR (recovered from Google) - Rugxulo, 07.09.2007, 04:14
        VESAMTTR (recovered from Google) - RayeR, 07.09.2007, 10:18
        VESAMTTR (recovered from Google) - rr, 07.09.2007, 10:45
        VESAMTTR (recovered from Google) - RayeR, 08.09.2007, 01:46
        VESAMTTR (recovered from Google) - Rugxulo, 08.09.2007, 07:03
        VESAMTTR (recovered from Google) - RayeR, 08.09.2007, 22:03
        VESAMTTR (recovered from Google) - rr, 08.09.2007, 22:49
        VESAMTTR (recovered from Google) - RayeR, 10.09.2007, 14:18
        VESAMTTR (recovered from Google) - Japheth, 06.09.2007, 07:17
        VESAMTTR (recovered from Google) - RayeR, 06.09.2007, 22:34
        VESAMTTR (recovered from Google) - rr, 06.09.2007, 16:51
        VESAMTTR (recovered from Google) - RayeR, 06.09.2007, 22:33
        VESAMTTR (recovered from Google) - Rugxulo, 07.09.2007, 05:11
        VESAMTTR (recovered from Google) - rr, 07.09.2007, 10:40
        VESAMTTR (recovered from Google) - rr, 07.09.2007, 10:40