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

Jiri Olsa
2020-04-23T11:28:52Z

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@google.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
>