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

Jiri Olsa
2021-06-07T18:28:58Z

On Sun, Jun 06, 2021 at 10:49:16PM -0700, Yonghong Song wrote:
>
>
> 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?

hum, I'm not what you mean.. what kernel code are you referring to?

thanks,
jirka