Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add support to record and check the accessed args

Steven Rostedt
2024-03-30T19:34:37Z

On Sat, 30 Mar 2024 11:18:29 +0800
梦龙董 <dongmenglong.8@bytedance.com> wrote:

> > If you really want to have thousands of functions, why not just register 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?
> >
>
> Ennn...I don't understand. The main purpose for
> me to use TRACING is:
>
> 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