1 files changed, 23 insertions, 0 deletions
diff --git a/lib/csu/tests/errno/errno_test.c b/lib/csu/tests/errno/errno_test.c
new file mode 100644
index 000000000000..d190c7fd2959
--- /dev/null
+++ b/lib/csu/tests/errno/errno_test.c
@@ -0,0 +1,23 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 Mark Johnston <markj@FreeBSD.org>
+ */
+
+#include <errno.h>
+#include <stdlib.h>
+
+static void __attribute__((constructor))
+f(void)
+{
+	errno = 42;
+}
+
+int
+main(void)
+{
+	/* errno must be zero upon program startup. */
+	if (errno != 0)
+		exit(1);
+	exit(0);
+}