linux-kernel - Re: [PATCH v3] tracing: precise log info for kretprobe addr err

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Date:   Tue, 26 Jan 2021 15:43:02 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Jianlin Lv <Jianlin.Lv@....com>, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] tracing: precise log info for kretprobe addr err

On Tue, 26 Jan 2021 21:20:59 +0100
Oleg Nesterov <oleg@...hat.com> wrote:

> > No, not wrong. Even offset != 0, if the symbol exists in the kernel,
> > kprobe_on_func_entry() will check it.  
> 
> Yes, but unless I am totally confused... if kprobe_on_func_entry() returns false,
> then trace_kprobe_create() should fail with BAD_RETPROBE even if offset == 0 ?

>From what I understand. kprobe_on_func_entry() can return false if you pass
in: "MOD:not_yet_loaded_module_func", but this is OK, because when the
module is loaded, and the "not_yet_loaded_module_func" exists, the
kretprobe will then be added.

The strchr(symbol,":") check is to see if "MOD:" (or some other ":" command)
is in the name, and we don't want it to fail if it is. Which is why we
should have that commented.

-- Steve