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

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On 11/25/21 1:33 PM, Arnaldo Carvalho de Melo wrote:
Em Tue, Nov 23, 2021 at 08:49:17PM -0800, Andrii Nakryiko escreveu:
On Tue, Nov 23, 2021 at 3:36 PM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> 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@xxxxxx> 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.

It is back to green, so I moved next to master, i.e. this series is now
on master.

Arnaldo,

Is it possible that we could cut a pahole release in the near future?
My kernel using btf_type_tag patch ([1]) needs a pahole version check. In old pahole versions, a warning about pointer type subtags not supported will be emitted and btf_type_tag attributes (as pointer type subtags) will be ignored.

  [1] https://lore.kernel.org/bpf/20211118184810.1846996-1-yhs@xxxxxx/

Thanks!


- Arnaldo

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@xxxxxxxxxx>

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




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