GPTrap: A VxD that Traps GP Faults

Revised: February 1993

GPTrap is a virtual device (VxD) that uses the
Hook_PM_Fault service to catch general protection (GP)
faults. When a GP fault occurs, GPTrap receives control
and executes an Interrupt 1. If execution is then
continued, control is passed to the next handler in the
fault handler chain.


To build GPTrap:

You will need Microsoft(R) Macro Assembler version 6.0 or
higher, as well as some special tools and include files;
see the "VxD Tools" and "VxD Include Files" abstracts to
copy these files to your development system. Configure
your development environment as described in the "VxD-Lite
Mini-DDK" technical article on the Microsoft Developer
Network CD.

If you have the Windows(TM) version 3.1 Device Driver Kit
(DDK), you can build its version of GPTrap using the DDK-
supplied MASM5.EXE (a special version of Macro Assembler
version 5.10). Note that the DDK samples require a
specific structure for the source and include
subdirectories, whereas the corresponding samples in the
 "VxD-Lite Mini-DDK" utilize the INCLUDE environment
variable to give you more flexibility in structuring your
development files.


To execute GPTrap:

1.  Run GPTRAP.EXE from the MS-DOS(R) prompt before
starting Windows. When enhanced-mode Windows starts up,
the VxD will load automatically. Thus, you do not need to
modify the SYSTEM.INI file to load this VxD. GPTrap will
automatically load each time you start Windows until you
reboot your computer; once rebooted, the stub loader is
cleared from memory and the VxD will not load.

If you prefer to have Windows load the VxD without first
executing it from the MS-DOS prompt, rename GPTRAP.EXE to
GPTRAP.386 and move it to the Windows SYSTEM subdirectory.
Add the line DEVICE=GPTRAP.386 to the [386Enh] section of
the SYSTEM.INI file.

2.  Run Windows in enhanced mode. The code responsible for
self-loading the VxD is in the VXDSTUB.ASM file and is
linked into the final VxD file by the STUB 'VXDSTUB.EXE'
module definition (.DEF) file statement. When executed
from the MS-DOS prompt, the VxDStub hooks Interrupt 2Fh,
terminates, and stays resident. When Microsoft Windows
initializes itself, the TSR responds to the Interrupt 2Fh,
AX=1605h broadcast and returns a structure that causes the
VxD to be loaded. This technique is discussed in the "TSR
Support in Microsoft Windows Version 3.1" technical
article on the Microsoft Developer Network CD.

GPTrap was built and tested under Microsoft Windows
version 3.1 using Microsoft MASM versions 6.0 and 6.1 and
the tools and include files provided in the "VxD-Lite Mini-
DDK."

KEYWORDS: PR-CD1; CD3 (revised)

THIS TOOL IS NOT SUPPORTED BY MICROSOFT CORPORATION. IT IS
PROVIDED "AS IS" BECAUSE WE BELIEVE IT MAY BE USEFUL TO
YOU. PLEASE DO NOT CONTACT MICROSOFT PRODUCT SUPPORT
SERVICES FOR SUPPORT OR ASSISTANCE SHOULD YOU HAVE
PROBLEMS USING THIS TOOL.

READ THE ASSOCIATED DOCUMENTATION, IF ANY, REGARDING THIS
TOOL PRIOR TO USING. ANY USE BY YOU OF THE TOOL IS AT YOUR
OWN RISK. THE TOOL IS PROVIDED FOR USE "AS IS" WITHOUT
WARRANTY OF ANY KIND. MICROSOFT AND ITS SUPPLIERS DISCLAIM
ALL WARRANTIES OF ANY KIND, EITHER EXPRESS OR IMPLIED,
INCLUDING, WITHOUT LIMITATION, IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
