Re: [PATCH 15/19] libbpf: Add support to link multi func tracing program

Yonghong Song
2021-06-07T05:50:26Z

On 6/5/21 4:10 AM, Jiri Olsa wrote:
> Adding support to link multi func tracing program
> through link_create interface.
>
> Adding special types for multi func programs:
>
> fentry.multi
> fexit.multi
>
> so you can define multi func programs like:
>
> SEC("fentry.multi/bpf_fentry_test*")
> int BPF_PROG(test1, unsigned long ip, __u64 a, __u64 b, __u64 c, __u64 d, __u64 e, __u64 f)
>
> that defines test1 to be attached to bpf_fentry_test* functions,
> and able to attach ip and 6 arguments.
>
> If functions are not specified the program needs to be attached
> manually.
>
> Adding new btf id related fields to bpf_link_create_opts and
> bpf_link_create to use them.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> tools/lib/bpf/bpf.c | 11 ++++++-
> tools/lib/bpf/bpf.h | 4 ++-
> tools/lib/bpf/libbpf.c | 72 ++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 85 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 86dcac44f32f..da892737b522 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -674,7 +674,8 @@ int bpf_link_create(int prog_fd, int target_fd,
> enum bpf_attach_type attach_type,
> const struct bpf_link_create_opts *opts)
> {
> - __u32 target_btf_id, iter_info_len;
> + __u32 target_btf_id, iter_info_len, multi_btf_ids_cnt;
> + __s32 *multi_btf_ids;
> union bpf_attr attr;
> int fd;
>
[...]
> @@ -9584,6 +9597,9 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog, int *btf_obj_fd,
> if (!name)
> return -EINVAL;
>
> + if (prog->prog_flags & BPF_F_MULTI_FUNC)
> + return 0;
> +
> for (i = 0; i < ARRAY_SIZE(section_defs); i++) {
> if (!section_defs[i].is_attach_btf)
> continue;
> @@ -10537,6 +10553,62 @@ static struct bpf_link *bpf_program__attach_btf_id(struct bpf_program *prog)
> return (struct bpf_link *)link;
> }
>
> +static struct bpf_link *bpf_program__attach_multi(struct bpf_program *prog)
> +{
> + char *pattern = prog->sec_name + prog->sec_def->len;
> + DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts);
> + enum bpf_attach_type attach_type;
> + int prog_fd, link_fd, cnt, err;
> + struct bpf_link *link = NULL;
> + __s32 *ids = NULL;
> +
> + prog_fd = bpf_program__fd(prog);
> + if (prog_fd < 0) {
> + pr_warn("prog '%s': can't attach before loaded\n", prog->name);
> + return ERR_PTR(-EINVAL);
> + }
> +
> + err = bpf_object__load_vmlinux_btf(prog->obj, true);
> + if (err)
> + return ERR_PTR(err);
> +
> + cnt = btf__find_by_pattern_kind(prog->obj->btf_vmlinux, pattern,
> + BTF_KIND_FUNC, &ids);
> + if (cnt <= 0)
> + return ERR_PTR(-EINVAL);

In kernel, looks like we support cnt = 0, here we error out.
Should we also error out in the kernel if cnt == 0?

> +
> + link = calloc(1, sizeof(*link));
> + if (!link) {
> + err = -ENOMEM;
> + goto out_err;
> + }
> + link->detach = &bpf_link__detach_fd;
> +
> + opts.multi_btf_ids = ids;
> + opts.multi_btf_ids_cnt = cnt;
> +
> + attach_type = bpf_program__get_expected_attach_type(prog);
> + link_fd = bpf_link_create(prog_fd, 0, attach_type, &opts);
> + if (link_fd < 0) {
> + err = -errno;
> + goto out_err;
> + }
> + link->fd = link_fd;
> + free(ids);
> + return link;
> +
> +out_err:
> + free(link);
> + free(ids);
> + return ERR_PTR(err);
> +}
> + …