On Thu, 28 Apr 2022 19:53:03 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > But that __fentry__ call is not part of __bpf_tramp_exit, actually. > > Whether to call it a bug or limitation is secondary. It marks > > __bpf_tramp_exit as attachable through kprobe/ftrace while it really > > isn't. > > I'm confused by what you mean by "marks __bpf_tramp_exit as attachable"? > What does? Where does it get that information? Does it read > available_filter_functions? OK, I think I see the issue you have. Because the functions shown in available_filter_functions which uses the simple "%ps" to show the function name: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/trace/ftrace.c#n3692 And the code that does the actual matching uses kallsyms_lookup() https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/trace/ftrace.c#n4017 Which appears not to match the function for the address, you can't pass in __bpf_tramp_exit because it wont match the symbol returned by kallsyms_lookup. This does indeed look like a bug in %ps. But in the mean time, I could open code %ps and see if that fixes it. I'll give it try. -- Steve
