comeillfoo / clr-profiler

A CLR (.NET Runtime) profiler written purely in Rust.

Brainstorming

How to create the Profiler COM object in Rust

• Must generate a .so file
  • Specify crate-type=cdylib
  • https://doc.rust-lang.org/reference/linkage.html
• The only symbol that needs exposed is DllGetClassObject
  • An example implementation in rust: https://github.com/Rantanen/intercom/blob/master/intercom-common/src/attributes/com_library.rs#L87
  • Rust function def if we were calling it in Rust from C (we're actually doing the opposite): https://docs.rs/winapi/0.3.8/winapi/um/combaseapi/fn.DllGetClassObject.html
• Must have a class that implements ICorProfilerCallback2 (or higher).
  • What does it mean to have a class if we only have C bindings (no C++)
  • What does it mean to implement an interface? COM has a concept of interfaces, but C/C++ doesn't (even though it's in the .h file as an "interface")

Basic flow is:

1. Some COM client (CLR in this case) calls DllGetClassObject, which populates a pointer ([out] parameter) to an instance of a struct that adheres to IClassFactory
2. The COM client then calls CreateInstance on the IClassFactory that it now has a handle to. This populates a pointer ([out] parameter) to an instance of a struct that adheres to ICorProfilerCallback9.
3. Now the COM client can call function pointers in this struct that it know will exist. Neat!

Some Helpful Resources:

• Docs on some of the weird Windows specific types (LPVOID, DWORD, HINSTANCE, etc...)
  • https://en.wikibooks.org/wiki/Windows_Programming/Handles_and_Data_Types

Some Links

• https://github.com/DataDog/dd-trace-dotnet
• https://docs.datadoghq.com/tracing/setup/dotnet/?tab=netcoreonlinux
• https://docs.microsoft.com/en-us/dotnet/framework/unmanaged-api/profiling/icorprofilercallback2-interface
• https://docs.microsoft.com/en-us/dotnet/framework/unmanaged-api/profiling/setting-up-a-profiling-environment
• https://github.com/microsoft/clr-samples/tree/master/ProfilingAPI
• https://github.com/microsoft/BPerf
• https://stackoverflow.com/questions/840501/how-do-function-pointers-in-c-work
• https://www.codeguru.com/cpp/com-tech/activex/misc/article.php/c5509/Simplifying-the-Concept-of-COM.htm
• https://docs.microsoft.com/en-us/windows/win32/com/implementing-iclassfactory
• https://docs.microsoft.com/en-us/windows/win32/api/unknwn/
• https://github.com/Rantanen/intercom/blob/master/intercom-common/src/attributes/com_library.rs#L87
• https://stackoverflow.com/questions/26117197/create-interface-to-c-function-pointers-in-rust
• https://www.reddit.com/r/rust/comments/4w6vjt/allocating_a_raw_double_pointer_in_rust/
• https://newrustacean.com/show_notes/e031/index.html
• http://jakegoulding.com/rust-ffi-omnibus/objects/
• https://docs.rs/libc/0.2.63/libc/enum.c_void.html
• https://docs.rs/winapi/0.3.8/winapi/ctypes/type.c_long.html
• https://docs.rs/intercom/0.2.0/intercom/struct.GUID.html
• https://opensource.stackexchange.com/questions/5143/how-to-mark-a-copied-apache-v2-piece-of-code
• https://www.codeproject.com/Articles/13601/COM-in-plain-C#CLASS
• https://gankra.github.io/blah/rust-layouts-and-abis/
• https://docs.rs/intercom/0.2.0/src/intercom/combox.rs.html#105-134

TODO

• Create facility to run tests against multiple .net versions. For example, here is linux setup for side-by-side .net core installations.
• A potential source of bugs in the ProfilerInfo struct, is when an S_OK hresult is returned, but one of the out pointer parameters can be null. These need explicitly checked if they are null and wrapped in an Option. If we just dereference, this is undefined behavior! The Microsoft documentation is spotty on which out parameters can be null. Sometimes it is mentioned in the remarks.