Re: [PATCH bpf-next v4 3/3] selftests/bpf: Test bpf_program__clone() attach_btf_id override

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Tue Mar 17, 2026 at 1:39 PM EDT, Mykyta Yatsenko wrote:
> From: Mykyta Yatsenko <yatsenko@meta.com>
>
> 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>

> ---
>  .../selftests/bpf/prog_tests/clone_attach_btf_id.c | 78 ++++++++++++++++++++++
>  .../selftests/bpf/progs/clone_attach_btf_id.c      | 13 ++++
>  2 files changed, 91 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/clone_attach_btf_id.c b/tools/testing/selftests/bpf/prog_tests/clone_attach_btf_id.c
> new file mode 100644
> index 000000000000..1c3e28e74606
> --- /dev/null
> +++ b/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 = {};
Nit: I think this is not necessary because the fields are populated in
the kernel in bpf_prog_get_info_by_fd().
> +	__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);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/clone_attach_btf_id.c b/tools/testing/selftests/bpf/progs/clone_attach_btf_id.c
> new file mode 100644
> index 000000000000..0ffa3ec3e1a0
> --- /dev/null
> +++ b/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;
> +}