KernelDebugRef - Debugging VM Start Sessions

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Kernel Debugger Reference

Introduction Installing the Kernel Debugger The T Terminal Emulator Entering the Debugger Expressions Operator Precedence Binary Operators Unary Operators Numbers Strings Symbol Files Using Kernel Debugger Commands The Breakpoint (BP) Command Breakpoint Commands External Commands Using Default Commands External Debugger Commands Setting Useful Breakpoints Debugging Kernel Device Drivers Debugging VM Start Sessions Debugging a Remote System Notices

Before you begin debugging in a VM Start session, you must establish interrupt vectors 1 and 3. Issue the command DD %%0 to see what the vectors should be, and then issue the following commands to set them to their correct values:

          E &0:4 12 67 00 1d
          E &0:c 57 67 00 1d

To debug a trap 6 or an incorrect-output problem, set a breakpoint at the VMINT21 entry point.

You can find the segment of FSFILTER by looking at the INT 20h or INT 21h vectors (0:80 and 0:84, respectively). The offset of VMINT21 is hex 330. Trace through all of the INT 21 calls until the error is observed. Run the test again to the last successful INT 21, then begin stepping through the code until the error is found.

A method of eliminating FSFILTER as the component with the problem is to set up a test case that is executed from the diskette. This way, you can execute a VM Start session without installing FSFILTER. If the problem still occurs, then FSFILTER is not the cause of the problem.