linux-kernel - Re: [PATCH v2 3/3] perf probe: Improve log for long event name failure

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Message-ID: <0e98dea9-cdd1-445c-813b-1fa652b72a7d@arm.com>
Date: Sat, 12 Oct 2024 21:52:04 +0100
From: Leo Yan <leo.yan@....com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>,
 Masami Hiramatsu <mhiramat@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 "Liang, Kan" <kan.liang@...ux.intel.com>, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] perf probe: Improve log for long event name
 failure

On 10/12/2024 4:44 PM, Leo Yan wrote:
> If a symbol name is longer than the maximum event length (64 bytes), the
> perf tool reports error:
> 
>   # perf probe -x test_cpp_mangle --add "this_is_a_very_very_long_print_data_abcdefghijklmnopqrstuvwxyz(int)"
>     snprintf() failed: -7; the event name nbase='this_is_a_very_very_long_print_data_abcdefghijklmnopqrstuvwxyz(int)' is too long
>     Error: Failed to add events.
> 
> An information is missed in the log that the symbol name and the event
> name can be set separately. Especially, this is recommended for adding
> probe for a long symbol.
> 
> This commit refines the log for reminding event syntax.
> 
> After:
> 
>   # perf probe -x test_cpp_mangle --add "this_is_a_very_very_long_print_data_abcdefghijklmnopqrstuvwxyz(int)"
>     snprintf() failed: -7; the event name is too long (>= 64 bytes)
>       Try to set event with syntax "[GROUP:]EVENT=this_is_a_very_very_long_print_data_abcdefghijklmnopqrstuvwxyz(int)"
>       Error: Failed to add events.

As the printed log is not suitable for all cases in this patch, please
ignore this patch and directly review version 3 for a updated log.

Thanks,
Leo

> 
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>  tools/perf/util/probe-event.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 224ec6818803..441daf4fb321 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -2760,7 +2760,9 @@ static int get_new_event_name(char *buf, size_t len, const char *base,
>  	/* Try no suffix number */
>  	ret = e_snprintf(buf, len, "%s%s", nbase, ret_event ? "__return" : "");
>  	if (ret < 0) {
> -		pr_warning("snprintf() failed: %d; the event name nbase='%s' is too long\n", ret, nbase);
> +		pr_warning("snprintf() failed: %d; the event name is too long (>= %d bytes)\n"
> +			   "  Try to set event with syntax \"[GROUP:]EVENT=%s\"\n",
> +			   ret, MAX_EVENT_NAME_LEN, nbase);
>  		goto out;
>  	}
>  	if (!strlist__has_entry(namelist, buf))