linux-kernel - Re: [PATCH] tracing: Fix synth event printk format for str fields

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Message-Id: <20250319211858.6d8166e3fb202e6e5a658557@kernel.org>
Date: Wed, 19 Mar 2025 21:18:58 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Douglas RAILLARD <douglas.raillard@....com>
Cc: rostedt@...dmis.org, Masami Hiramatsu <mhiramat@...nel.org>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Fix synth event printk format for str fields

Hi,

On Tue, 18 Mar 2025 18:09:38 +0000
Douglas RAILLARD <douglas.raillard@....com> wrote:

> From: Douglas Raillard <douglas.raillard@....com>
> 
> The printk format for synth event uses "%.*s" to print string fields,
> but then only passes the pointer part as var arg.
> 
> Add the missing precision var arg.

I'm not sure what you want to. Would you mean showing the string length too?
But I think actual output(*) shows only string, right?

(*) the output data which can be read from `trace` file.

Thank you,

> 
> Signed-off-by: Douglas Raillard <douglas.raillard@....com>
> ---
>  kernel/trace/trace_events_synth.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
> index e3f7d09e5512..274b9b1d9f7d 100644
> --- a/kernel/trace/trace_events_synth.c
> +++ b/kernel/trace/trace_events_synth.c
> @@ -620,7 +620,8 @@ static int __set_synth_event_print_fmt(struct synth_event *event,
>  		if (event->fields[i]->is_string &&
>  		    event->fields[i]->is_dynamic)
>  			pos += snprintf(buf + pos, LEN_OR_ZERO,
> -				", __get_str(%s)", event->fields[i]->name);
> +				", (int)__get_dynamic_array_len(%s), __get_str(%s)",
> +				event->fields[i]->name, event->fields[i]->name);
>  		else if (event->fields[i]->is_stack)
>  			pos += snprintf(buf + pos, LEN_OR_ZERO,
>  				", __get_stacktrace(%s)", event->fields[i]->name);
> -- 
> 2.43.0
> 


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