Added gc_handler to properly handle circular references.

Author: SakiTakamachi

ext/pdo/pdo_stmt.c

@@ -2077,6 +2077,23 @@ static zend_function *dbstmt_method_get(zend_object **object_pp, zend_string *me
 	return fbc;
 }
 
+static HashTable *dbstmt_get_gc(zend_object *object, zval **gc_data, int *gc_count)
+{
+	pdo_stmt_t *stmt = php_pdo_stmt_fetch_object(object);
+	*gc_data = &stmt->fetch.into;
+	*gc_count = 1;
+
+	/**
+	 * If there are no dynamic properties and the default property is 1 (that is, there is only one property
+	 * of string that does not participate in GC), there is no need to call zend_std_get_properties().
+	 */
+	if (object->properties == NULL && object->ce->default_properties_count <= 1) {
+		return NULL;
+	} else {
+		return zend_std_get_properties(object);
+	}
+}
+
 zend_object_handlers pdo_dbstmt_object_handlers;
 zend_object_handlers pdo_row_object_handlers;
 
@@ -2495,6 +2512,7 @@ void pdo_stmt_init(void)
 	pdo_dbstmt_object_handlers.get_method = dbstmt_method_get;
 	pdo_dbstmt_object_handlers.compare = zend_objects_not_comparable;
 	pdo_dbstmt_object_handlers.clone_obj = NULL;
+	pdo_dbstmt_object_handlers.get_gc = dbstmt_get_gc;
 
 	pdo_row_ce = register_class_PDORow();
 	pdo_row_ce->create_object = pdo_row_new;

ext/pdo/tests/gh16703.phpt

@@ -0,0 +1,43 @@
+--TEST--
+GH-16703: Memory leak of setFetchMode()
+--EXTENSIONS--
+pdo
+--SKIPIF--
+<?php
+$dir = getenv('REDIR_TEST_DIR');
+if (false == $dir) die('skip no driver');
+require_once $dir . 'pdo_test.inc';
+PDOTest::skip();
+?>
+--FILE--
+<?php
+
+class TestStmt extends PDOStatement
+{
+    public $name;
+}
+
+$db = new PDO(
+    getenv('PDOTEST_DSN'),
+    getenv('PDOTEST_USER') ?: null,
+    getenv('PDOTEST_PASS') ?: null,
+    [PDO::ATTR_STATEMENT_CLASS => [TestStmt::class]],
+);
+
+$db->exec('CREATE TABLE gh16703 (name varchar(255))');
+$db->exec("INSERT INTO gh16703 (name) VALUES ('test_name')");
+
+$stmt = $db->query('SELECT name FROM gh16703');
+$t = $stmt;
+$stmt->setFetchMode(PDO::FETCH_INTO, $stmt);
+$stmt->fetch();
+echo "done!\n";
+?>
+--CLEAN--
+<?php
+require_once getenv('REDIR_TEST_DIR') . 'pdo_test.inc';
+$db = PDOTest::factory();
+$db->exec('DROP TABLE gh16703');
+?>
+--EXPECT--
+done!