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'.
The series touches many functional areas: BTF.ext handling; object access,
introspection, and linking; generation of normal and "light" skeletons.
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/
Earlier versions and related discussion of the series are here:
v1: https://lore.kernel.org/bpf/cover.1724216108.git.tony.ambardar@xxxxxxxxx/
v2: https://lore.kernel.org/bpf/cover.1724313164.git.tony.ambardar@xxxxxxxxx/
v3: https://lore.kernel.org/bpf/cover.1724843049.git.tony.ambardar@xxxxxxxxx/
v4: https://lore.kernel.org/bpf/cover.1724976539.git.tony.ambardar@xxxxxxxxx/
Feedback and suggestions are welcome!
Best regards,
Tony
Changelog:
---------
v4 -> v5: (feedback from Andrii and Eduard)
- add separate functions to byte-swap info metadata and records, and
ensure ordering so record bswaps occur when metadata is native endian
- use new and existing macros to iterate through info sections/records,
and check embedded record sizes match that of info structs used
- drop use of <cough> evil callbacks
- move setting swapped_endian flag to after byte-swapping functions are
called during initialization, allowing funcs to infer endianness and
drop a 'bool native' call parameter
- simplify byte-swapping macro used to generate light skeleton, and use
internal lib funcs to swap info records instead of assuming all __u32
- change info bswap library funcs to void return
- rework/consolidate new debug statements to reduce their number
- remove some unneeded handling of impossible errors, and drop a safety
check already handled elsewhere
- add and clarify some comments
v3 -> v4:
- fix a use-after-free ELF data-handling error causing rare CI failures
- move bswap functions for func/line/core-relo records to internal header
- use bswap functions also for info blobs in light skeleton
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 | 242 +++++++++++++++++++++++++--
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 | 191 +++++++++++++++------
tools/lib/bpf/libbpf.c | 57 +++++--
tools/lib/bpf/libbpf.map | 2 +
tools/lib/bpf/libbpf_internal.h | 43 ++++-
tools/lib/bpf/linker.c | 80 +++++++--
tools/lib/bpf/relo_core.c | 2 +-
tools/lib/bpf/skel_internal.h | 3 +-
tools/testing/selftests/bpf/Makefile | 7 +-
13 files changed, 529 insertions(+), 106 deletions(-)
--
2.34.1
