[PATCH 2/2] perf trace: Handle NULL pointer dereference in trace__syscall_info()

[Leo Yan]

trace__init_bpf_map_syscall_args() invokes trace__syscall_info() to
retrieve system calls information, it always passes NULL for 'evsel'
argument; when id is an invalid value then the logging will try to
output event name, this triggers NULL pointer dereference.

This patch directly uses string "unknown" for event name when 'evsel'
is NULL pointer.

Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
---
 tools/perf/builtin-trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 5cd74651db4c..49dfb2fd393b 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1764,7 +1764,7 @@ static struct syscall *trace__syscall_info(struct trace *trace,
 		static u64 n;
 
 		pr_debug("Invalid syscall %d id, skipping (%s, %" PRIu64 ")\n",
-			 id, perf_evsel__name(evsel), ++n);
+			 id, evsel ? perf_evsel__name(evsel) : "unknown", ++n);
 		return NULL;
 	}
 
-- 
2.17.1