| Message ID | cover.1724843049.git.tony.ambardar@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | libbpf, selftests/bpf: Support cross-endian usage | expand |
On Wed, Aug 28, 2024 at 04:11:50AM -0700, Tony Ambardar wrote: > Hello all, [snip] > Changelog: > --------- > v2 -> v3: (feedback from Andrii) > - improve some log and commit message formatting > - restructure BTF.ext endianness safety checks and byte-swapping > - use BTF.ext info record definitions for swapping, require BTF v1 > - follow BTF API implementation more closely for BTF.ext > - explicitly reject loading non-native endianness program into kernel > - simplify linker output byte-order setting > - drop redundant safety checks during linking > - simplify endianness macro and improve blob setup code for light skel > - no unexpected test failures after cross-compiling x86_64 -> s390x Sadly, shortly after posting v3 I hit a strange new issue in CI testing. Existing code in bpf_object__elf_finish() doesn't zero Ehdr references after freeing the related ELF data, allowing use of stale endian data which can be reallocated and overwritten, leading to rare, confusing CI errors like: test_tailcall_count:PASS:open fentry_obj file 0 nsec test_tailcall_count:PASS:find fentry prog 0 nsec test_tailcall_count:PASS:set_attach_target subprog_tail 0 nsec libbpf: object 'tailcall_bpf2bp' is not native endianness test_tailcall_count:FAIL:load fentry_obj unexpected error: -4003 (errno 4003) #333/13 tailcalls/tailcall_bpf2bpf_fentry:FAIL I have a minor patch to fix this but will wait for feedback on v3 before posting it together with any further requested changes in a v4. Apologies for the extra churn, and I'll attach the pending patch for reference. Thanks, Tony
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: --------- v2 -> v3: (feedback from Andrii) - improve some log and commit message formatting - restructure BTF.ext endianness safety checks and byte-swapping - use BTF.ext info record definitions for swapping, require BTF v1 - follow BTF API implementation more closely for BTF.ext - explicitly reject loading non-native endianness program into kernel - simplify linker output byte-order setting - drop redundant safety checks during linking - simplify endianness macro and improve blob setup code for light skel - no unexpected test failures after cross-compiling x86_64 -> s390x 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 | 230 ++++++++++++++++++++++++--- 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 | 185 ++++++++++++++++----- tools/lib/bpf/libbpf.c | 39 +++-- tools/lib/bpf/libbpf.map | 2 + tools/lib/bpf/libbpf_internal.h | 17 +- tools/lib/bpf/linker.c | 92 +++++++++-- tools/lib/bpf/relo_core.c | 2 +- tools/lib/bpf/skel_internal.h | 3 +- tools/testing/selftests/bpf/Makefile | 7 +- 13 files changed, 488 insertions(+), 97 deletions(-)