[PATCH bpf-next v2 0/2] tools/resolve_btfids: fix cross-compilation to non-host endianness

[Viktor Malik <vmalik@redhat.com>]

The .BTF_ids section is pre-filled with zeroed BTF ID entries during the
build and afterwards patched by resolve_btfids with correct values.
Since resolve_btfids always writes in host-native endianness, it relies
on libelf to do the translation when the target ELF is cross-compiled to
a different endianness (this was introduced in commit 61e8aeda9398
("bpf: Fix libelf endian handling in resolv_btfids")).

Unfortunately, the translation will corrupt the flags fields of SET8
entries because these were written during vmlinux compilation and are in
the correct endianness already. This will lead to numerous selftests
failures such as:

    $ sudo ./test_verifier 502 502
    #502/p sleepable fentry accept FAIL
    Failed to load prog 'Invalid argument'!
    bpf_fentry_test1 is not sleepable
    verification time 34 usec
    stack depth 0
    processed 0 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
    Summary: 0 PASSED, 0 SKIPPED, 1 FAILED

Since it's not possible to instruct libelf to translate just certain
values, let's manually bswap the flags in resolve_btfids when needed, so
that libelf then translates everything correctly.

The first patch of the series refactors resolve_btfids by using types
from btf_ids.h instead of accessing the BTF ID data using magic offsets.

Viktor Malik (2):
  tools/resolve_btfids: Refactor set sorting with types from btf_ids.h
  tools/resolve_btfids: fix cross-compilation to non-host endianness

 tools/bpf/resolve_btfids/main.c | 55 ++++++++++++++++++++++++++++-----
 tools/include/linux/btf_ids.h   |  9 ++++++
 2 files changed, 56 insertions(+), 8 deletions(-)

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2.43.0