Investigate ftrace and live patching

[geofft]

A question from today's Linux Plumbers Conference session: do things like ftrace and kgraft work properly? Do they work properly in a GCC-compiled host kernel (i.e., LLVM for Rust and GCC for C)?

I think they do, because I think this support just uses __fentry__ which both LLVM and GCC implement (I think) in the same way, but we should test it.

[alex]

I'm not super familiar with ftrace, can someone suggest what a test for this might look like?