> 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
>>
