Re: [PATCH dwarves v2 0/4] btf: support btf_type_tag attribute

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, Nov 23, 2021 at 3:36 PM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Tue, Nov 23, 2021 at 10:32:18AM -0800, Andrii Nakryiko escreveu:
> > On Mon, Nov 22, 2021 at 8:56 PM Yonghong Song <yhs@fb.com> wrote:
> > >
> > > btf_type_tag is a new llvm type attribute which is used similar
> > > to kernel __user/__rcu attributes. The format of btf_type_tag looks like
> > >   __attribute__((btf_type_tag("tag1")))
> > > For the case where the attribute applied to a pointee like
> > >   #define __tag1 __attribute__((btf_type_tag("tag1")))
> > >   #define __tag2 __attribute__((btf_type_tag("tag2")))
> > >   int __tag1 * __tag1 __tag2 *g;
> > > the information will be encoded in dwarf.
> > >
> > > In BTF, the attribute is encoded as a new kind
> > > BTF_KIND_TYPE_TAG and latest bpf-next supports it.
> > >
> > > The patch added support in pahole, specifically
> > > converts llvm dwarf btf_type_tag attributes to
> > > BTF types. Please see individual patches for details.
> > >
> > > Changelog:
> > >   v1 -> v2:
> > >      - reorg an if condition to reduce nesting level.
> > >      - add more comments to explain how to chain type tag types.
> > >
> > > Yonghong Song (4):
> > >   libbpf: sync with latest libbpf repo
> > >   dutil: move DW_TAG_LLVM_annotation definition to dutil.h
> > >   dwarf_loader: support btf_type_tag attribute
> > >   btf_encoder: support btf_type_tag attribute
> > >
> >
> > I thought that v1 was already applied, but either way LGTM. I'm not
>
> To the next branch, and the libbpf pahole CI is failing, since a few
> days, can you please take a look?

We've had Clang regression which Yonghong fixed very quickly, but then
we were blocked on Clang nightly builds being broken for days. Seems
like we got a new Clang today, so hopefully libbpf CI will be back to
green again.

>
> > super familiar with the DWARF loader parts, so I mostly just read it
> > very superficially :)
>
> I replaced the patches that changed, re-added the S-o-B for Yonghong and
> tested it with llvm-project HEAD.
>
> > Acked-by: Andrii Nakryiko <andrii@kernel.org>
>
> Adding it to the csets.
>
> Thanks!
>
> - Arnaldo
>
> >
> > >  btf_encoder.c  |   7 +++
> > >  dutil.h        |   4 ++
> > >  dwarf_loader.c | 140 ++++++++++++++++++++++++++++++++++++++++++++++---
> > >  dwarves.h      |  38 +++++++++++++-
> > >  lib/bpf        |   2 +-
> > >  pahole.c       |   8 +++
> > >  6 files changed, 190 insertions(+), 9 deletions(-)
> > >
> > > --
> > > 2.30.2
> > >
>
> --
>
> - Arnaldo