VAX/VMS Device Driver Debugging

This document serves as a comprehensive guide for debugging device drivers within the VAX/VMS operating system environment, emphasizing that due to their kernel-mode operation at high interrupt priority levels, even minor errors can lead to system crashes.

The guide introduces key debugging tools provided by VMS:

• DELTA Debugger: For debugging user images and programs transitioning from user to kernel mode (IPL 0).
• XDELTA Debugger: Specifically for debugging operating system drivers in kernel mode (IPL > 0), typically accessed from the console.
• System Dump Analyzer (SDA): Utilized for static analysis of active systems or crash dump files.

Detailed procedures are provided for:

• Analyzing Bugcheck Output: Step-by-step instructions to interpret console bugcheck listings and SDA dump files to identify the instruction causing a system crash within a driver. This includes correlating register dumps, kernel/interrupt stacks, and driver map files.
• Bootstrapping and Invoking XDELTA: Commands and methods for activating XDELTA on different VAX systems and for debugging routines at various Interrupt Priority Levels (IPLs), including using JSB G^INISBRK for elevated IPLs.
• Using the CHMK Program: A technique to dynamically examine kernel-mode data structures by changing process mode to kernel, with a strong caution against modifying data to prevent system crashes.
• Command References: Tables summarizing commands and functions for both DELTA/XDELTA and SDA, covering operations like displaying/modifying memory, setting breakpoints, and examining system information.
• Driver Testing Hints: A detailed set of recommendations for thorough driver testing, including developing comprehensive test programs, systematically testing FDT routines, simulating various conditions (timeout, powerfail, I/O cancel), strategic placement of breakpoints, and preparing diagnostic programs.
• Common Driver Problems: A list of frequent issues encountered during driver development, such as access violations, NULL process errors, MWAIT state issues, and random behavior, along with their common causes.

The document underscores the necessity of rigorous testing and provides the tools and methodologies to diagnose and resolve issues in VAX/VMS device drivers effectively.