linux-kernel - [PATCH v1] perf symbol: Avoid an undefined behavior warning

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Message-Id: <20230914044233.1550195-1-irogers@google.com>
Date:   Wed, 13 Sep 2023 21:42:32 -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@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        James Clark <james.clark@....com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1] perf symbol: Avoid an undefined behavior warning

The node (nd) may be NULL and pointer arithmetic on NULL is undefined
behavior. Move the computation of next below the NULL check on the
node.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/symbol.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 3f36675b7c8f..5b54d2639df4 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -202,11 +202,10 @@ void symbols__fixup_duplicate(struct rb_root_cached *symbols)
 		curr = rb_entry(nd, struct symbol, rb_node);
 again:
 		nd = rb_next(&curr->rb_node);
-		next = rb_entry(nd, struct symbol, rb_node);
-
 		if (!nd)
 			break;
 
+		next = rb_entry(nd, struct symbol, rb_node);
 		if (curr->start != next->start)
 			continue;
 
-- 
2.42.0.459.ge4e396fd5e-goog