Microsoft KB Archive/111593

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BUG: DPMI Function 0203h Does Not Report Error

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Q111593

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The information in this article applies to:


 * Microsoft Windows Software Development Kit (SDK) 3.1

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SYMPTOMS
Using the MS-DOS Protected Mode Interface (DPMI) function 0203h (set processor exception handler vector) to set an exception handler does not report an error (carry flag set) if the selector:offset pair is invalid.

RESOLUTION
The pointer to the exception handler must be validated with other means if it is necessary to check the pointer for validity. Other means of checking a code pointer for validity include using IsBadCodePtr or the LAR (load access rights) protected-mode CPU instruction.

STATUS
Microsoft has confirmed this to be a bug in Windows version 3.1. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION
The problem with DPMI function 0203h can be illustrated with the following code segment:

  mov     edx, dword ptr BogusOffset mov    cx, word ptr BogusSelector ; Set Processor Exception Handler Vector mov    ax, 203h mov    bx, 7 int    31h jc     Error       ; never jumps to Error

REFERENCE
The IsBadCodePtr function is documented in the Windows 3.1 SDK "Programmer's Reference, Volume 2: Functions" manual. The LAR instruction is documented in the Intel 386 or 486 "Programmer's Reference" or in "Microsoft's 80386/80486 Programming Guide" by Microsoft Press.

Additional query words: buglist3.10 3.10

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Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310