On Fri, Sep 10, 2021 at 9:39 AM Yonghong Song <yhs@xxxxxx> wrote:
>
>
>
> On 9/8/21 10:33 PM, Andrii Nakryiko wrote:
> > On Wed, Sep 8, 2021 at 10:28 PM Andrii Nakryiko
> > <andrii.nakryiko@xxxxxxxxx> wrote:
> >>
> >> On Tue, Sep 7, 2021 at 4:01 PM Yonghong Song <yhs@xxxxxx> wrote:
> >>>
> >>> added bpftool support to dump BTF_KIND_TAG information.
> >>> The new bpftool will be used in later patches to dump
> >>> btf in the test bpf program object file.
> >>>
> >
> > What should be done for `bpftool btf dump file <path> format c` if BTF
> > contains btf_tag? Should it ignore it silently? Should it error out?
> > Or should we corrupt output (as will be the case right now, I think)?
>
> Currently it is silently ignored. The attribute information is mostly
> used in the kernel by verification purpose and the kernel uses its own
> btf to check.
>
> Adding such attributes to vmlinux.h, bpf program BTF will contain these
> attributes but they may not be used by the kernel verifier at least
> for now.
>
> So I think we can delay this as a followup if there is a real need.
Sounds good. Just wanted to confirm that we won't get some libbpf
warning emitted inside vmlinux.h, making it non-compilable.
>
> >
> >>> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> >>> ---
> >>> tools/bpf/bpftool/btf.c | 18 ++++++++++++++++++
> >>> 1 file changed, 18 insertions(+)
> >>>
> >>> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> >>> index f7e5ff3586c9..89c17ea62d8e 100644
> >>> --- a/tools/bpf/bpftool/btf.c
> >>> +++ b/tools/bpf/bpftool/btf.c
> >>> @@ -37,6 +37,7 @@ static const char * const btf_kind_str[NR_BTF_KINDS] = {
> >>> [BTF_KIND_VAR] = "VAR",
> >>> [BTF_KIND_DATASEC] = "DATASEC",
> >>> [BTF_KIND_FLOAT] = "FLOAT",
> >>> + [BTF_KIND_TAG] = "TAG",
> >>> };
> >>>
> >>> struct btf_attach_table {
> >>> @@ -347,6 +348,23 @@ static int dump_btf_type(const struct btf *btf, __u32 id,
> >>> printf(" size=%u", t->size);
> >>> break;
> >>> }
> >>> + case BTF_KIND_TAG: {
> >>> + const struct btf_tag *tag = (const void *)(t + 1);
> >>> +
> >>> +
> >>
> >> extra empty line?
> >>
> >>> + if (json_output) {
> >>> + jsonw_uint_field(w, "type_id", t->type);
> >>> + if (btf_kflag(t))
> >>> + jsonw_int_field(w, "comp_id", -1);
> >>> + else
> >>> + jsonw_uint_field(w, "comp_id", tag->comp_id);
> >>> + } else if (btf_kflag(t)) {
> >>> + printf(" type_id=%u, comp_id=-1", t->type);
> >>> + } else {
> >>> + printf(" type_id=%u, comp_id=%u", t->type, tag->comp_id);
> >>> + }
> >>
> >> here not using kflag would be more natural as well ;)
> >>
> >>> + break;
> >>> + }
> >>> default:
> >>> break;
> >>> }
> >>> --
> >>> 2.30.2
> >>>
