Re: [PATCH bpf-next v2 00/11] bpf: add support for new btf kind BTF_KIND_TAG

["Jose E. Marchesi" <jose.marchesi@oracle.com>]

> cc Jose E. Marchesi
>
> Hi, Jose, just let you know that the BTF format for BTF_KIND_TAG is
> changed since v1 as the new format can simplify kernel/libbpf
> implementation. Thanks!

Noted.  Thanks for the update.

>
> On 9/13/21 8:51 AM, Yonghong Song wrote:
>> LLVM14 added support for a new C attribute ([1])
>>    __attribute__((btf_tag("arbitrary_str")))
>> This attribute will be emitted to dwarf ([2]) and pahole
>> will convert it to BTF. Or for bpf target, this
>> attribute will be emitted to BTF directly ([3], [4]).
>> The attribute is intended to provide additional
>> information for
>>    - struct/union type or struct/union member
>>    - static/global variables
>>    - static/global function or function parameter.
>> This new attribute can be used to add attributes
>> to kernel codes, e.g., pre- or post- conditions,
>> allow/deny info, or any other info in which only
>> the kernel is interested. Such attributes will
>> be processed by clang frontend and emitted to
>> dwarf, converting to BTF by pahole. Ultimiately
>> the verifier can use these information for
>> verification purpose.
>> The new attribute can also be used for bpf
>> programs, e.g., tagging with __user attributes
>> for function parameters, specifying global
>> function preconditions, etc. Such information
>> may help verifier to detect user program
>> bugs.
>> After this series, pahole dwarf->btf converter
>> will be enhanced to support new llvm tag
>> for btf_tag attribute. With pahole support,
>> we will then try to add a few real use case,
>> e.g., __user/__rcu tagging, allow/deny list,
>> some kernel function precondition, etc,
>> in the kernel.
>> In the rest of the series, Patches 1-2 had
>> kernel support. Patches 3-4 added
>> libbpf support. Patch 5 added bpftool
>> support. Patches 6-10 added various selftests.
>> Patch 11 added documentation for the new kind.
>>    [1] https://reviews.llvm.org/D106614
>>    [2] https://reviews.llvm.org/D106621
>>    [3] https://reviews.llvm.org/D106622
>>    [4] https://reviews.llvm.org/D109560
>> Changelog:
>>    v1 -> v2:
>>      - BTF ELF format changed in llvm ([4] above),
>>        so cross-board change to use the new format.
>>      - Clarified in commit message that BTF_KIND_TAG
>>        is not emitted by bpftool btf dump format c.
>>      - Fix various comments from Andrii.
>> Yonghong Song (11):
>>    btf: change BTF_KIND_* macros to enums
>>    bpf: support for new btf kind BTF_KIND_TAG
>>    libbpf: rename btf_{hash,equal}_int to btf_{hash,equal}_int_tag
>>    libbpf: add support for BTF_KIND_TAG
>>    bpftool: add support for BTF_KIND_TAG
>>    selftests/bpf: test libbpf API function btf__add_tag()
>>    selftests/bpf: change NAME_NTH/IS_NAME_NTH for BTF_KIND_TAG format
>>    selftests/bpf: add BTF_KIND_TAG unit tests
>>    selftests/bpf: test BTF_KIND_TAG for deduplication
>>    selftests/bpf: add a test with a bpf program with btf_tag attributes
>>    docs/bpf: add documentation for BTF_KIND_TAG
>>   Documentation/bpf/btf.rst                     |  27 +-
>>   include/uapi/linux/btf.h                      |  52 +--
>>   kernel/bpf/btf.c                              | 120 +++++++
>>   tools/bpf/bpftool/btf.c                       |  12 +
>>   tools/include/uapi/linux/btf.h                |  52 +--
>>   tools/lib/bpf/btf.c                           |  85 ++++-
>>   tools/lib/bpf/btf.h                           |  15 +
>>   tools/lib/bpf/btf_dump.c                      |   3 +
>>   tools/lib/bpf/libbpf.c                        |  31 +-
>>   tools/lib/bpf/libbpf.map                      |   5 +
>>   tools/lib/bpf/libbpf_internal.h               |   2 +
>>   tools/testing/selftests/bpf/btf_helpers.c     |   7 +-
>>   tools/testing/selftests/bpf/prog_tests/btf.c  | 318 ++++++++++++++++--
>>   .../selftests/bpf/prog_tests/btf_tag.c        |  14 +
>>   .../selftests/bpf/prog_tests/btf_write.c      |  21 ++
>>   tools/testing/selftests/bpf/progs/tag.c       |  39 +++
>>   tools/testing/selftests/bpf/test_btf.h        |   3 +
>>   17 files changed, 736 insertions(+), 70 deletions(-)
>>   create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_tag.c
>>   create mode 100644 tools/testing/selftests/bpf/progs/tag.c
>>