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
> +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?
> +
> 3. BTF Kernel API
> *****************
>
> --
> 2.30.2
>
