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Date: Sat, 30 Mar 2024 15:37:22 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: =?UTF-8?B?5qKm6b6Z6JGj?= <dongmenglong.8@bytedance.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>, Jiri Olsa
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Subject: Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add
 support to record and check the accessed args
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On Sat, 30 Mar 2024 11:18:29 +0800
=E6=A2=A6=E9=BE=99=E8=91=A3 <dongmenglong.8@bytedance.com> wrote:

> > If you really want to have thousands of functions, why not just registe=
r it
> > with ftrace itself. It will give you the arguments via the ftrace_regs
> > structure. Can't you just register a program as the callback?
> > =20
>=20
> Ennn...I don't understand. The main purpose for
> me to use TRACING is:
>=20
> 1. we can directly access the memory, which is more
>    efficient.

I'm not sure what you mean by the above. Access what memory?

> 2. we can obtain the function args in FEXIT, which
>     kretprobe can't do it. And this is the main reason.

I didn't mention kretprobe. If you need access to the exit of the function,
you can use Masami's fgraph update.

 fentry -> ftrace_trampoline -> your_code

For fgraph:

 fentry -> ftrace_trampoline -> fgraph [sets up return call] -> your_entry_=
code

 function ret -> fgraph_ret_handler -> your_exit_code

And you will be able to pass data from the entry to the exit code,
including parameters.

-- Steve