linux-kernel - Re: [PATCH v4] trace/kprobe: Display the actual notrace function when rejecting a probe

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Date: Sun, 17 Dec 2023 16:18:01 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Naveen N Rao <naveen@...nel.org>
Cc: <linux-kernel@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Srikar Dronamraju <srikar@...ux.ibm.com>
Subject: Re: [PATCH v4] trace/kprobe: Display the actual notrace function
 when rejecting a probe

On Thu, 14 Dec 2023 10:47:02 +0530
Naveen N Rao <naveen@...nel.org> wrote:

> Trying to probe update_sd_lb_stats() using perf results in the below
> message in the kernel log:
> 	trace_kprobe: Could not probe notrace function _text
> 
> This is because 'perf probe' specifies the kprobe location as an offset
> from '_text':
> 	$ sudo perf probe -D update_sd_lb_stats
> 	p:probe/update_sd_lb_stats _text+1830728
> 
> However, the error message is misleading and doesn't help convey the
> actual notrace function that is being probed. Fix this by looking up the
> actual function name that is being probed. With this fix, we now get the
> below message in the kernel log:
> 	trace_kprobe: Could not probe notrace function update_sd_lb_stats.constprop.0
> 

OK, this looks good to me. let me pick this.

Thank you!

> Signed-off-by: Naveen N Rao <naveen@...nel.org>
> ---
> v4: Use printk format specifier %ps with probe address to lookup the 
> symbol, as suggested by Masami.
> 
>  kernel/trace/trace_kprobe.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 3d7a180a8427..0017404d6e8d 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -487,8 +487,8 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
>  		return -EINVAL;
>  
>  	if (within_notrace_func(tk)) {
> -		pr_warn("Could not probe notrace function %s\n",
> -			trace_kprobe_symbol(tk));
> +		pr_warn("Could not probe notrace function %ps\n",
> +			(void *)trace_kprobe_address(tk));
>  		return -EINVAL;
>  	}
>  
> 
> base-commit: 4758560fa268cecfa1144f015aa9f2525d164b7e
> -- 
> 2.43.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>