linux-kernel - [RFC PATCH v2 10/23] perf expr: print a debug message for division by zero

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Message-Id: <20200507140819.126960-11-irogers@google.com>
Date:   Thu,  7 May 2020 07:08:06 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     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>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Andi Kleen <ak@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Kim Phillips <kim.phillips@....com>,
        linux-kernel@...r.kernel.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>
Subject: [RFC PATCH v2 10/23] 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@...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) {
+					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; }
-- 
2.26.2.526.g744177e7f7-goog