perf expr: Print a debug message for division by zero

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>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Haiyan Song <haiyanx.song@intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200501173333.227162-11-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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) {
+					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; }