On Fri, Sep 10, 2021 at 9:40 AM Yonghong Song <yhs@xxxxxx> wrote:
>
>
>
> On 9/8/21 10:42 PM, Andrii Nakryiko wrote:
> > On Tue, Sep 7, 2021 at 4:01 PM Yonghong Song <yhs@xxxxxx> wrote:
> >>
> >> Add BTF_KIND_TAG documentation in btf.rst.
> >>
> >> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> >> ---
> >> Documentation/bpf/btf.rst | 30 ++++++++++++++++++++++++++++--
> >> 1 file changed, 28 insertions(+), 2 deletions(-)
> >>
> >
> > [...]
> >
> >> +2.2.17 BTF_KIND_TAG
> >> +~~~~~~~~~~~~~~~~~~~
> >> +
> >> +``struct btf_type`` encoding requirement:
> >> + * ``name_off``: offset to a non-empty string
> >> + * ``info.kind_flag``: 0 for tagging ``type``, 1 for tagging member/argument of the ``type``
> >> + * ``info.kind``: BTF_KIND_TAG
> >> + * ``info.vlen``: 0
> >> + * ``type``: ``struct``, ``union``, ``func`` or ``var``
> >> +
> >> +``btf_type`` is followed by ``struct btf_tag``.::
> >> +
> >> + struct btf_tag {
> >> + __u32 comp_id;
> >> + };
> >> +
> >> +The ``name_off`` encodes btf_tag attribute string.
> >> +If ``info.kind_flag`` is 1, the attribute is attached to the ``type``.
> >
> > This contradicts "info.kind_flag" description above
>
> will remove info.kind_flag stuff in the next revision.
>
> >
> >> +If ``info.kind_flag`` is 0, the attribute is attached to either a
> >> +``struct``/``union`` member or a ``func`` argument.
> >> +Hence the ``type`` should be ``struct``, ``union`` or
> >> +``func``, and ``btf_tag.comp_id``, starting from 0,
> >> +indicates which member or argument is attached with
> >> +the attribute.
> >
> > Does the kernel validate this restriction for the VAR target type?
> > I.e., if we have kind_flag == 0 (member of type), we should disallow
> > VAR, right?
>
> Yes, I even has a selftest for that.
Great, must have missed it on initial review pass.
>
> >
> >> +
> >> 3. BTF Kernel API
> >> *****************
> >>
> >> --
> >> 2.30.2
> >>
