This is quite easy to do with a low-level debugger, like x64dbg (for instance). Say, if I have a running native process I can attach to it, set a breakpoint, and then step through native code with it.
Is there a similar debugger but for .NET, that would allow me to do what I listed above?
Try using https://github.com/dnSpyEx/dnSpy. It has NET decompiler, debugger and you can make changes directly in C# code, compile it and save changes into existing dll or exe module.
*.ni.dll assemblies (native images), as in C:\Windows\assembly\NativeImages_v4.0.30319_64\Microsoft.Df7c88f51#\7f6d8ef6224b79741cbfa39fe91b6702\Microsoft.Data.Mashup.ProviderCommon.ni.dll. Where would I apply that registry setting then?
In Visual Studio (not Visual Studio Code), go to menu Debug -> "Attach to Process", pick up the process from the list. Now you can press "pause" / "Break All" in Visual Studio to suspend all process threads and start debugging them.
This works regardless of if the process is written in C++ or .NET.
Visual Studio will show the stack trace and even source code if available. (In .NET even if source code is not available if you have installed a plugin for Visual Studio like Redgate Reflector Pro or https://github.com/icsharpcode/ILSpy).
For debugging a service process, you have to wait until the execution enters your program, you cannot attach a debugger during the SCM execution. The simplest way to do this is to add an blind loop to your code and once attached, exit the loop with the debugger (by changing the value of the sentinel variable) like
int i = 0;
while (i == 0) {
i++;
i--;
}
For dealing with issues like "cannot see this variable value because it has been optimized away" you can disable CLR optimizations, I have used this switch (AllowOptimize), see stackoverflow.com/a/279593/1001395 (in a .ini file of the same name like the assembly you are debugging, ie System.Data.dll.ini) <= this works in .NET classic.
[.NET Framework Debugging Control]
GenerateTrackingInfo=1
AllowOptimize=0
