How can I get current values of locals and parameters on the stack?

Question

In a .NET application I have some points where I need to collect some debug info about the current thread state. I can obtain some information new StackTrace() constructor. In particular, I can get the list of current stack frames, including corresponding MethodInfo objects, which can provide me the IL code, the number of local variables and parameters and parameter names.

How can I get current values of these locals and parameters (at least of primitive types)?

I am not able to manually attach any debuggers to the application, but the application can spawn new processes if needed.

Answer 1

Reflection, what you are using to obtain MethodInfo and other details, uses metadata created at compile time -- that is, the data you are accessing has no relation to run-time data, which is what you want.

You mentioned that you can't use a debugger, and you're right, because in production code there's usually no debug symbols loaded in your assembly; a debugger would be no use there.

A important thing here is that, per .NET architecture, once you run an assembly, a "jitter" runs and transforms your IL code into native code; The result is that what is loaded in memory is pure machine code that you can't very easily hack into to obtain values (although theoretically possible). Another point mentioned are optimizations - as long as they are on, you can expect methods to disappear (being inlined), execution order may be changed and variables replaced by literals. The compiler does a lot of stuff to get your code to run faster.

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Although I can't see a good solution for obtaining locals' values in run-time, I think there are ways to obtain parameters' value using interception techniques. Take a look at what PostSharp can do for you.