linux-kernel - Re: [PATCH v2 10/11] perf expr: print a debug message for division by zero

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Message-ID: <20200423112837.GE1136647@krava>
Date:   Thu, 23 Apr 2020 13:28:37 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Haiyan Song <haiyanx.song@...el.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        John Garry <john.garry@...wei.com>,
        Leo Yan <leo.yan@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Paul Clarke <pc@...ibm.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 10/11] perf expr: print a debug message for division
 by zero

On Wed, Apr 22, 2020 at 03:04:29PM -0700, Ian Rogers wrote:
> If an expression yields 0 and is then divided-by/modulus-by then the
> parsing aborts. Add a debug error message to better enable debugging
> when this happens.
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/expr.y | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/expr.y b/tools/perf/util/expr.y
> index 54260094b947..21e82a1e11a2 100644
> --- a/tools/perf/util/expr.y
> +++ b/tools/perf/util/expr.y
> @@ -103,8 +103,18 @@ expr:	  NUMBER
>  	| expr '+' expr		{ $$ = $1 + $3; }
>  	| expr '-' expr		{ $$ = $1 - $3; }
>  	| expr '*' expr		{ $$ = $1 * $3; }
> -	| expr '/' expr		{ if ($3 == 0) YYABORT; $$ = $1 / $3; }
> -	| expr '%' expr		{ if ((long)$3 == 0) YYABORT; $$ = (long)$1 % (long)$3; }
> +	| expr '/' expr		{ if ($3 == 0) {
> +					pr_debug("division by zero\n");
> +					YYABORT;
> +				  }
> +				  $$ = $1 / $3;
> +	                        }
> +	| expr '%' expr		{ if ((long)$3 == 0) {

is that (long) cast necessary? it's missing for the '/' case

jirka

> +					pr_debug("division by zero\n");
> +					YYABORT;
> +				  }
> +				  $$ = (long)$1 % (long)$3;
> +	                        }
>  	| '-' expr %prec NEG	{ $$ = -$2; }
>  	| '(' if_expr ')'	{ $$ = $2; }
>  	| MIN '(' expr ',' expr ')' { $$ = $3 < $5 ? $3 : $5; }
> -- 
> 2.26.2.303.gf8c07b1a785-goog
>