10.2 Debugging P-Code

Certain Microsoft compilers can generate space-saving p-code instead of machine code. P-code cannot be run by the processor itself because it is not native machine code. However, when you compile a program into p-code, LINK and the Make P-Code (MPC) utility add an interpreter to your program that reads and interprets p-code instructions.

The interpreter implements a “stack machine.” The p-code instructions generally assume operands on the stack rather than take explicit registers or addresses. Because p-code instructions do not explicitly specify operands, they are extremely small. The trade-off for compact code is reduced execution speed. You use p-code when saving space is more important than speed.

CodeView allows you to debug p-code in the same way you debug native code. At the source level, debugging works the same way for p-code as it does for native code. With CodeView's p-code execution model, you can view p-code instructions in Mixed and Assembly modes just as you view native machine instructions. The Register window displays the p-code registers and the top eight entries of the p-code stack. If your program contains both p-code routines and native routines, CodeView automatically switches between p-code display and native display. You can also force CodeView to stay in Native mode when you want to view the native machine code of the p-code interpreter itself.

The rest of this section describes:

How to configure CodeView to use the p-code execution model.

How to prepare p-code programs for debugging.

Techniques for debugging p-code.

Limitations while debugging p-code.