[v7,bpf-next,00/10] Add BTF_KIND_FLOAT support

Message

Ilya Leoshkevich Feb. 26, 2021, 8:22 p.m. UTC

Some BPF programs compiled on s390 fail to load, because s390
arch-specific linux headers contain float and double types.

Introduce support for such types by representing them using the new
BTF_KIND_FLOAT. This series deals with libbpf, bpftool, in-kernel BTF
parser as well as selftests and documentation.

There are also pahole and LLVM parts:

* https://github.com/iii-i/dwarves/commit/btf-kind-float-v2
* https://reviews.llvm.org/D83289

but they should go in after the libbpf part is integrated.

---

v0: https://lore.kernel.org/bpf/[e-mail]/
v0 -> v1: Per Andrii's suggestion, remove the unnecessary trailing u32.

v1: https://lore.kernel.org/bpf/[e-mail]/
v1 -> v2: John noticed that sanitization corrupts BTF, because new and
          old sizes don't match. Per Yonghong's suggestion, use a
          modifier type (which has the same size as the float type) as
          a replacement.
          Per Yonghong's suggestion, add size and alignment checks to
          the kernel BTF parser.

v2: https://lore.kernel.org/bpf/[e-mail]/
v2 -> v3: Based on Yonghong's suggestions: Use BTF_KIND_CONST instead of
          BTF_KIND_TYPEDEF and make sure that the C code generated from
          the sanitized BTF is well-formed; fix size calculation in
          tests and use NAME_TBD everywhere; limit allowed sizes to 2,
          4, 8, 12 and 16 (this should also fix m68k and nds32le
          builds).

v3: https://lore.kernel.org/bpf/[e-mail]/
v3 -> v4: More fixes for the Yonghong's findings: fix the outdated
          comment in bpf_object__sanitize_btf() and add the error
          handling there (I've decided to check uint_id and uchar_id
          too in order to simplify debugging); add bpftool output
          example; use div64_u64_rem() instead of % in order to fix the
          linker error.
          Also fix the "invalid BTF_INFO" test (new commit, #4).

v4: https://lore.kernel.org/bpf/[e-mail]/
v4 -> v5: Fixes for the Andrii's findings: Use BTF_KIND_STRUCT instead
          of BTF_KIND_TYPEDEF for sanitization; check byte_sz in
          libbpf; move btf__add_float; remove relo support; add a dedup
          test (new commit, #7).

v5: https://lore.kernel.org/bpf/[e-mail]/
v5 -> v6: Fixes for further findings by Andrii: split whitespace issue
          fix into a separate patch; add 12-byte float to "float test #1,
          well-formed".

v6: https://lore.kernel.org/bpf/[e-mail]/
v6 -> v7: John suggested to add a comment explaining why sanitization
          does not preserve the type name, as well as what effect it has
          on running the code on the older kernels.
          Yonghong has asked to add a comment explaining why we are not
          checking the alignment very precisely in the kernel.
          John suggested to add a bpf_core_field_size test (commit #9).

Based on Alexei's feedback [1] I'm proceeding with the BTF_KIND_FLOAT
approach.

[1] https://lore.kernel.org/bpf/[e-mail]/

Ilya Leoshkevich (10):
  bpf: Add BTF_KIND_FLOAT to uapi
  libbpf: Fix whitespace in btf_add_composite() comment
  libbpf: Add BTF_KIND_FLOAT support
  tools/bpftool: Add BTF_KIND_FLOAT support
  selftests/bpf: Use the 25th bit in the "invalid BTF_INFO" test
  bpf: Add BTF_KIND_FLOAT support
  selftest/bpf: Add BTF_KIND_FLOAT tests
  selftests/bpf: Add BTF_KIND_FLOAT to the existing deduplication tests
  selftests/bpf: Add BTF_KIND_FLOAT to test_core_reloc_size
  bpf: Document BTF_KIND_FLOAT in btf.rst

 Documentation/bpf/btf.rst                     |  17 +-
 include/uapi/linux/btf.h                      |   5 +-
 kernel/bpf/btf.c                              |  83 ++++++++-
 tools/bpf/bpftool/btf.c                       |   8 +
 tools/bpf/bpftool/btf_dumper.c                |   1 +
 tools/include/uapi/linux/btf.h                |   5 +-
 tools/lib/bpf/btf.c                           |  51 ++++-
 tools/lib/bpf/btf.h                           |   6 +
 tools/lib/bpf/btf_dump.c                      |   4 +
 tools/lib/bpf/libbpf.c                        |  29 ++-
 tools/lib/bpf/libbpf.map                      |   5 +
 tools/lib/bpf/libbpf_internal.h               |   2 +
 tools/testing/selftests/bpf/btf_helpers.c     |   4 +
 tools/testing/selftests/bpf/prog_tests/btf.c  | 176 ++++++++++++++++--
 .../selftests/bpf/prog_tests/core_reloc.c     |   1 +
 .../selftests/bpf/progs/core_reloc_types.h    |   5 +
 .../bpf/progs/test_core_reloc_size.c          |   3 +
 tools/testing/selftests/bpf/test_btf.h        |   3 +
 18 files changed, 385 insertions(+), 23 deletions(-)

Comments

Alexei Starovoitov March 5, 2021, 2:36 a.m. UTC | #1

On Fri, Feb 26, 2021 at 12:23 PM Ilya Leoshkevich <[e-mail]> wrote:
>
> Some BPF programs compiled on s390 fail to load, because s390
> arch-specific linux headers contain float and double types.
>
> Introduce support for such types by representing them using the new
> BTF_KIND_FLOAT. This series deals with libbpf, bpftool, in-kernel BTF
> parser as well as selftests and documentation.
>
> There are also pahole and LLVM parts:
>
> * https://github.com/iii-i/dwarves/commit/btf-kind-float-v2
> * https://reviews.llvm.org/D83289
...
> v6 -> v7: John suggested to add a comment explaining why sanitization
>           does not preserve the type name, as well as what effect it has
>           on running the code on the older kernels.
>           Yonghong has asked to add a comment explaining why we are not
>           checking the alignment very precisely in the kernel.
>           John suggested to add a bpf_core_field_size test (commit #9).

Applied without patch 9, since it crashes current llvm.
Please work with Yonghong to land llvm support
and resubmit the selftest along with an update to selftest/bpf/README.rst
that needs to explain which llvm commit is needed to pass the test.

Thanks!