Re: [PATCH bpf-next RESEND v2] libbpf: Fix expected_attach_type set when kernel not support

[Tao Chen]

在 2024/9/14 04:46, Andrii Nakryiko 写道:
> On Fri, Sep 13, 2024 at 9:44 AM Tao Chen <chen.dylane@xxxxxxxxx> wrote:
> > The commit "5902da6d8a52" set expected_attach_type again with
> > filed of bpf_program after libpf_prepare_prog_load, which makes
> > expected_attach_type = 0 no sense when kenrel not support the
> > attach_type feature, so fix it.
> >
> > Fixes: 5902da6d8a52 ("libbpf: Add uprobe multi link support to bpf_program__attach_usdt")
> > Suggested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx>
> > ---
> >   tools/lib/bpf/libbpf.c | 6 ++----
> >   1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > Change list:
> > - v1 -> v2:
> >      - restore the original initialization way suggested by Jiri
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 219facd0e66e..df2244397ba1 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -7353,7 +7353,7 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
> >
> >          /* special check for usdt to use uprobe_multi link */
> >          if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK))
> > -               prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
> > +               opts->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
>
> Ok, took me a bit to understand what the issue is. But the above is
> not quite correct, for the above case of setting
> BPF_TRACE_UPROBE_MULTI we do want to record BPF_TRACE_UPROBE_MULTI in
> prog->expected_attach_type, because user might want to query that
> later.
>
> So I agree with the part of the fix below, but here I think we need
> *both* update opts' and prog's expected_attach_type, so we will have:
>
>         prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
>         opts->expected_attach_type = BPF_TRACE_UPROBE_MULTI;
>
> pw-bot: cr
>
> >          if ((def & SEC_ATTACH_BTF) && !prog->attach_btf_id) {
> >                  int btf_obj_fd = 0, btf_type_id = 0, err;
> > @@ -7443,6 +7443,7 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
> >          load_attr.attach_btf_id = prog->attach_btf_id;
> >          load_attr.kern_version = kern_version;
> >          load_attr.prog_ifindex = prog->prog_ifindex;
> > +       load_attr.expected_attach_type = prog->expected_attach_type;
> >
> >          /* specify func_info/line_info only if kernel supports them */
> >          if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
> > @@ -7474,9 +7475,6 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
> >                  insns_cnt = prog->insns_cnt;
> >          }
> >
> > -       /* allow prog_prepare_load_fn to change expected_attach_type */
> > -       load_attr.expected_attach_type = prog->expected_attach_type;
> > -
> >          if (obj->gen_loader) {
> >                  bpf_gen__prog_load(obj->gen_loader, prog->type, prog->name,
> >                                     license, insns, insns_cnt, &load_attr,
> > --
> > 2.25.1

Hi, Andrii, thank you for your reply. I will send v3 as you suggested.

--
Best Regards
Dylane Chen