[PATCH bpf-next v2 02/13] selftests/bpf: Clone a program that calls a module kfunc

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Prepare an object whose program calls a kfunc of bpf_testmod and load
the program through bpf_program__clone(), the way veristat loads
programs. The module BTF fd sits in slot 1 of the fd_array of the
object and slot 0 is empty; the clone used to pass the fill index of
that array as fd_array_cnt, which made the kernel resolve slot 0 and
fail the load with "fd 0 is not pointing to valid bpf_map or btf".

Cc: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../bpf/prog_tests/clone_module_kfunc.c       | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/clone_module_kfunc.c

diff --git a/tools/testing/selftests/bpf/prog_tests/clone_module_kfunc.c b/tools/testing/selftests/bpf/prog_tests/clone_module_kfunc.c
new file mode 100644
index 000000000000..fa6ccbaa7fd9
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/clone_module_kfunc.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include "kfunc_call_test.skel.h"
+
+/*
+ * bpf_program__clone() loads a program from a prepared object with the
+ * fd_array of the object, where module BTF fds start at slot 1 and slot 0 is
+ * empty. It used to pass the fill index of that array as fd_array_cnt, which
+ * made the kernel resolve slot 0 and fail the load.
+ */
+void test_clone_module_kfunc(void)
+{
+	struct kfunc_call_test *skel;
+	int err, fd;
+
+	skel = kfunc_call_test__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	err = bpf_object__prepare(skel->obj);
+	if (!ASSERT_OK(err, "prepare"))
+		goto out;
+
+	fd = bpf_program__clone(skel->progs.kfunc_call_test1, NULL);
+	if (ASSERT_GE(fd, 0, "clone"))
+		close(fd);
+out:
+	kfunc_call_test__destroy(skel);
+}
-- 
2.53.0-Meta