Implementing line-level profiling

Question

The last week or so I've been playing with the CLR Profiling API, as a pet project for the summer.

I started thinking about how ANTS and DotTrace implement line-level profiling. I can't see anything related to this in the Profiling API, so I assume they've got something proprietary.

I'm looking for pointers or thoughts on how this is implemented by them.

Do they inject MSIL code when the code is being JIT'ed?

Answer 1

CLR Profiling API support out of the box only tracing on Enter & Leave level. This can be done using ICorProfilerInfo::SetEnterLeaveFunctionHooks

In order to trace at finer level weaving of IL is required. You can use these open source profilers code as references:

• OpenCover
• PartCover

Both weave code during JITCompilationStarted callback.