selftests/bpf: Test bpf_program__clone() attach_btf_id override

Add a test that verifies bpf_program__clone() respects caller-provided
attach_btf_id in bpf_prog_load_opts.

The BPF program has SEC("fentry/bpf_fentry_test1"). It is cloned twice
from the same prepared object: first with no opts, verifying the
callback resolves attach_btf_id from sec_name to bpf_fentry_test1;
then with attach_btf_id overridden to bpf_fentry_test2, verifying the
loaded program is actually attached to bpf_fentry_test2. Both results
are checked via bpf_prog_get_info_by_fd().

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260317-veristat_prepare-v4-3-74193d4cc9d9@meta.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/clone_attach_btf_id.c

@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta */
+#include <test_progs.h>
+#include "clone_attach_btf_id.skel.h"
+
+/*
+ * Test that bpf_program__clone() respects caller-provided attach_btf_id
+ * override via bpf_prog_load_opts.
+ *
+ * The BPF program has SEC("fentry/bpf_fentry_test1"). Clone it twice
+ * from the same prepared object: first with no opts (callback resolves
+ * attach_btf_id from sec_name), then with attach_btf_id overridden to
+ * bpf_fentry_test2. Verify each loaded program's attach_btf_id via
+ * bpf_prog_get_info_by_fd().
+ */
+
+static int get_prog_attach_btf_id(int prog_fd)
+{
+	struct bpf_prog_info info = {};
+	__u32 info_len = sizeof(info);
+	int err;
+
+	err = bpf_prog_get_info_by_fd(prog_fd, &info, &info_len);
+	if (err)
+		return err;
+	return info.attach_btf_id;
+}
+
+void test_clone_attach_btf_id(void)
+{
+	struct clone_attach_btf_id *skel;
+	int fd1 = -1, fd2 = -1, err;
+	int btf_id_test1, btf_id_test2;
+
+	btf_id_test1 = libbpf_find_vmlinux_btf_id("bpf_fentry_test1", BPF_TRACE_FENTRY);
+	if (!ASSERT_GT(btf_id_test1, 0, "find_btf_id_test1"))
+		return;
+
+	btf_id_test2 = libbpf_find_vmlinux_btf_id("bpf_fentry_test2", BPF_TRACE_FENTRY);
+	if (!ASSERT_GT(btf_id_test2, 0, "find_btf_id_test2"))
+		return;
+
+	skel = clone_attach_btf_id__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	err = bpf_object__prepare(skel->obj);
+	if (!ASSERT_OK(err, "obj_prepare"))
+		goto out;
+
+	/* Clone with no opts — callback resolves BTF from sec_name */
+	fd1 = bpf_program__clone(skel->progs.fentry_handler, NULL);
+	if (!ASSERT_GE(fd1, 0, "clone_default"))
+		goto out;
+	ASSERT_EQ(get_prog_attach_btf_id(fd1), btf_id_test1,
+		  "attach_btf_id_default");
+
+	/*
+	 * Clone with attach_btf_id override pointing to a different
+	 * function. The BPF program never accesses arguments, so the
+	 * load succeeds regardless of signature mismatch.
+	 */
+	LIBBPF_OPTS(bpf_prog_load_opts, opts,
+		    .attach_btf_id = btf_id_test2,
+	);
+	fd2 = bpf_program__clone(skel->progs.fentry_handler, &opts);
+	if (!ASSERT_GE(fd2, 0, "clone_override"))
+		goto out;
+	ASSERT_EQ(get_prog_attach_btf_id(fd2), btf_id_test2,
+		  "attach_btf_id_override");
+
+out:
+	if (fd1 >= 0)
+		close(fd1);
+	if (fd2 >= 0)
+		close(fd2);
+	clone_attach_btf_id__destroy(skel);
+}

tools/testing/selftests/bpf/progs/clone_attach_btf_id.c

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(fentry_handler, int a)
+{
+	return 0;
+}