With just the vtables, Kernel#set_trace_func is reasonably easy - you can do it just by introducing thunks that proxy to the real method after calling the trace function. Wasteful, though, but easy to patch in/out.

The moment you inline, I think it's still possible to do reasonably ok using ptrace as long as sufficient debug info is kept to identify call sites. In both cases I think that for my project, if I ever get to looking at set_trace_func, I'll probably require a compiler option to enable debug info, as it's not exactly frequently used. Alternatively use the approach we've discussed and fall back to a "slow path".

Binding is basically a closure that captures all local variables and arguments of its context, so it's not that tricky in most cases as long as you can identify it and alias / copy variables into a separate environment. This is already how I handle block references to surrounding variables - by hoisting the creation of the environment for the closure up to the start of the relevant scope and aliasing all mentioned variables.

eval() of course complicates this massively, but then eval() complicates everything massively - and doubly so for ahead-of-time compilation.