linux-kernel - Re: [PATCH v1] perf parse-events: Avoid string for PE_BP_COLON, PE_BP

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Date:   Tue, 13 Jun 2023 16:41:43 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Rob Herring <robh@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf parse-events: Avoid string for PE_BP_COLON,
 PE_BP_SLASH

Em Tue, Jun 13, 2023 at 11:26:29AM -0700, Ian Rogers escreveu:
> There's no need to read the string ':' or '/' for PE_BP_COLON or
> PE_BP_SLASH and doing so causes parse-events.y to leak memory.
> 
> The original patch has a committer note about not using these tokens
> presumably as yacc spotted they were a memory leak because no
> %destructor could be run. Remove the unused token workaround as there
> is now no value associated with these tokens.

It looked like the compiler was the one warning (-Wother) about args not
being used, didn't made it clear those were possible memory leaks :-\

 util/parse-events.y:508.24-34: warning: unused value: $3 [-Wother]
   508 | PE_PREFIX_MEM PE_VALUE PE_BP_SLASH PE_VALUE PE_BP_COLON PE_MODIFIER_BP opt_event_config

Anyway, I'll apply and test your patch.

- Arnaldo
 
> Fixes: f0617f526cb0 ("perf parse: Allow config terms with breakpoints")
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/parse-events.h | 4 ----
>  tools/perf/util/parse-events.l | 4 ++--
>  tools/perf/util/parse-events.y | 9 ---------
>  3 files changed, 2 insertions(+), 15 deletions(-)
> 
> diff --git a/tools/perf/util/parse-events.h b/tools/perf/util/parse-events.h
> index 5fdc1f33f57e..b0eb95f93e9c 100644
> --- a/tools/perf/util/parse-events.h
> +++ b/tools/perf/util/parse-events.h
> @@ -228,10 +228,6 @@ void parse_events_error__handle(struct parse_events_error *err, int idx,
>  void parse_events_error__print(struct parse_events_error *err,
>  			       const char *event);
>  
> -static inline void parse_events_unused_value(const void *x __maybe_unused)
> -{
> -}
> -
>  #ifdef HAVE_LIBELF_SUPPORT
>  /*
>   * If the probe point starts with '%',
> diff --git a/tools/perf/util/parse-events.l b/tools/perf/util/parse-events.l
> index 7629af3d5c7c..99335ec586ae 100644
> --- a/tools/perf/util/parse-events.l
> +++ b/tools/perf/util/parse-events.l
> @@ -315,13 +315,13 @@ r0x{num_raw_hex}	{ return str(yyscanner, PE_RAW); }
>  	 * are the same, so trailing context can be used disambiguate the two
>  	 * cases.
>  	 */
> -":"/{modifier_bp}	{ return str(yyscanner, PE_BP_COLON); }
> +":"/{modifier_bp}	{ return PE_BP_COLON; }
>  	/*
>  	 * The slash before memory length can get mixed up with the slash before
>  	 * config terms. Fortunately config terms do not start with a numeric
>  	 * digit, so trailing context can be used disambiguate the two cases.
>  	 */
> -"/"/{digit}		{ return str(yyscanner, PE_BP_SLASH); }
> +"/"/{digit}		{ return PE_BP_SLASH; }
>  "/"/{non_digit}		{ BEGIN(config); return '/'; }
>  {num_dec}		{ return value(yyscanner, 10); }
>  {num_hex}		{ return value(yyscanner, 16); }
> diff --git a/tools/perf/util/parse-events.y b/tools/perf/util/parse-events.y
> index 0c3d086cc22a..9f28d4b5502f 100644
> --- a/tools/perf/util/parse-events.y
> +++ b/tools/perf/util/parse-events.y
> @@ -80,8 +80,6 @@ static void free_list_evsel(struct list_head* list_evsel)
>  %type <str> PE_LEGACY_CACHE
>  %type <str> PE_MODIFIER_EVENT
>  %type <str> PE_MODIFIER_BP
> -%type <str> PE_BP_COLON
> -%type <str> PE_BP_SLASH
>  %type <str> PE_EVENT_NAME
>  %type <str> PE_KERNEL_PMU_EVENT PE_PMU_EVENT_FAKE
>  %type <str> PE_DRV_CFG_TERM
> @@ -510,9 +508,6 @@ PE_PREFIX_MEM PE_VALUE PE_BP_SLASH PE_VALUE PE_BP_COLON PE_MODIFIER_BP opt_event
>  	struct list_head *list;
>  	int err;
>  
> -	parse_events_unused_value(&$3);
> -	parse_events_unused_value(&$5);
> -
>  	list = alloc_list();
>  	ABORT_ON(!list);
>  	err = parse_events_add_breakpoint(_parse_state, list,
> @@ -531,8 +526,6 @@ PE_PREFIX_MEM PE_VALUE PE_BP_SLASH PE_VALUE opt_event_config
>  	struct list_head *list;
>  	int err;
>  
> -	parse_events_unused_value(&$3);
> -
>  	list = alloc_list();
>  	ABORT_ON(!list);
>  	err = parse_events_add_breakpoint(_parse_state, list,
> @@ -550,8 +543,6 @@ PE_PREFIX_MEM PE_VALUE PE_BP_COLON PE_MODIFIER_BP opt_event_config
>  	struct list_head *list;
>  	int err;
>  
> -	parse_events_unused_value(&$3);
> -
>  	list = alloc_list();
>  	ABORT_ON(!list);
>  	err = parse_events_add_breakpoint(_parse_state, list,
> -- 
> 2.41.0.162.gfafddb0af9-goog
> 

-- 

- Arnaldo