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Message-ID: <20220428200945.5f6a5ba2@gandalf.local.home> Date: Thu, 28 Apr 2022 20:09:45 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Andrii Nakryiko <andrii.nakryiko@...il.com> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Masami Hiramatsu <mhiramat@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...omium.org> Subject: Re: [RFC bpf-next 4/4] selftests/bpf: Add attach bench test On Thu, 28 Apr 2022 19:53:03 -0400 Steven Rostedt <rostedt@...dmis.org> 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
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