[PATCH bpf-next 0/3] libbpf: auto-resize relocatable LOAD/STORE instructions

[Andrii Nakryiko <andriin@fb.com>]

Patch set implements logic in libbpf to auto-adjust memory size (1-, 2-, 4-,
8-bytes) of load/store (LD/ST/STX) instructions which have BPF CO-RE field
offset relocation associated with it. In practice this means transparent
handling of 32-bit kernels, both pointer and unsigned integers. Signed
integers are not relocatable with zero-extending loads/stores, so libbpf
poisons them and generates a warning. If/when BPF gets support for sign-extending
loads/stores, it would be possible to automatically relocate them as well.

All the details are contained in patch #1 comments and commit message.
Patch #2 is a simple change in libbpf to make advanced testing with custom BTF
easier. Patch #3 validates correct uses of auto-resizable loads, as well as
check that libbpf fails invalid uses.

I'd really appreciate folks that use BPF on 32-bit architectures to test this
out with their BPF programs and report if there are any problems with the
approach.

Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Tony Ambardar <tony.ambardar@gmail.com>

Andrii Nakryiko (3):
  libbpf: support safe subset of load/store instruction resizing with
    CO-RE
  libbpf: allow specifying both ELF and raw BTF for CO-RE BTF override
  selftests/bpf: validate libbpf's auto-sizing of LD/ST/STX instructions

 tools/lib/bpf/libbpf.c                        | 146 ++++++++++++-
 .../selftests/bpf/prog_tests/core_autosize.c  | 199 ++++++++++++++++++
 .../selftests/bpf/progs/test_core_autosize.c  | 148 +++++++++++++
 3 files changed, 483 insertions(+), 10 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/core_autosize.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_core_autosize.c

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2.24.1