[bpf-next,v2,0/8] libbpf, selftests/bpf: Support cross-endian usage

Message

Tony Ambardar Aug. 22, 2024, 9:24 a.m. UTC

From: Tony Ambardar <[e-mail]>

Hello all,

This patch series targets a long-standing BPF usability issue - the lack
of general cross-compilation support - by enabling cross-endian usage of
libbpf and bpftool, as well as supporting cross-endian build targets for
selftests/bpf.

Benefits include improved BPF development and testing for embedded systems
based on e.g. big-endian MIPS, more build options e.g for s390x systems,
and better accessibility to the very latest test tools e.g. 'test_progs'.

Initial development and testing used mips64, since this arch makes
switching the build byte-order trivial and is thus very handy for A/B
testing. However, it lacks some key features (bpf2bpf call, kfuncs, etc)
making for poor selftests/bpf coverage.

Final testing takes the kernel and selftests/bpf cross-built from x86_64
to s390x, and runs the result under QEMU/s390x. That same configuration
could also be used on kernel-patches/bpf CI for regression testing endian
support or perhaps load-sharing s390x builds across x86_64 systems.

This thread includes some background regarding testing on QEMU/s390x and
the generally favourable results:
    https://lore.kernel.org/bpf/ZsEcsaa3juxxQBUf@kodidev-ubuntu/

Feedback and suggestions are welcome!

Best regards,
Tony


Changelog:
---------
v1 -> v2:
 - fixed a light skeleton bug causing test_progs 'map_ptr' failure
 - simplified some BTF.ext related endianness logic
 - remove an 'inline' usage related to CI checkpatch failure
 - improve some formatting noted by checkpatch warnings
 - unexpected 'test_progs' failures drop 3 -> 2 (x86_64 to s390x cross)



Tony Ambardar (8):
  libbpf: Improve log message formatting
  libbpf: Fix header comment typos for BTF.ext
  libbpf: Fix output .symtab byte-order during linking
  libbpf: Support BTF.ext loading and output in either endianness
  libbpf: Support opening bpf objects of either endianness
  libbpf: Support linking bpf objects of either endianness
  libbpf: Support creating light skeleton of either endianness
  selftests/bpf: Support cross-endian building

 tools/lib/bpf/bpf_gen_internal.h     |   1 +
 tools/lib/bpf/btf.c                  | 168 ++++++++++++++++++++++--
 tools/lib/bpf/btf.h                  |   3 +
 tools/lib/bpf/btf_dump.c             |   2 +-
 tools/lib/bpf/btf_relocate.c         |   2 +-
 tools/lib/bpf/gen_loader.c           | 187 ++++++++++++++++++++-------
 tools/lib/bpf/libbpf.c               |  26 +++-
 tools/lib/bpf/libbpf.map             |   2 +
 tools/lib/bpf/libbpf_internal.h      |  17 ++-
 tools/lib/bpf/linker.c               | 108 +++++++++++++---
 tools/lib/bpf/relo_core.c            |   2 +-
 tools/lib/bpf/skel_internal.h        |   3 +-
 tools/testing/selftests/bpf/Makefile |   7 +-
 13 files changed, 444 insertions(+), 84 deletions(-)