The current stable LLVM BPF backend fails to compile the BPF selftests due to a compiler bug. The bug has been fixed in trunk, but that fix hasn't landed in the binary packages I'm using yet (Fedora arm64). Without this workaround the tests don't compile for me.

This patch triggers a preprocessor warning on LLVM versions that definitely have the bug. The test may be conservative (ie, I'm not sure if 9.1 will have the fix), but it should at least make the current set of stable releases work together.

See https://reviews.llvm.org/D69438 for more information on the fix. I obtained the workaround from https://lore.kernel.org/linux-kselftest/aed8eda7-df20-069b-ea14-f06628984566...

Fixes: 20a9ad2e7136 ("selftests/bpf: add CO-RE relocs array tests") Signed-off-by: Palmer Dabbelt palmerdabbelt@google.com --- .../testing/selftests/bpf/progs/test_core_reloc_arrays.c | 8 ++++++++ 1 file changed, 8 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c b/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c index 89951b684282..e5eafdab80a4 100644 --- a/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c +++ b/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c @@ -43,15 +43,23 @@ int test_core_arrays(void *ctx) /* in->a[2] */ if (CORE_READ(&out->a2, &in->a[2])) return 1; +#if defined(__clang__) && (__clang_major__ < 10) && (__clang_minor__ < 1) +# warning "clang 9.0 SEGVs on multidimensional arrays, see https://reviews.llvm.org/D69438" +#else /* in->b[1][2][3] */ if (CORE_READ(&out->b123, &in->b[1][2][3])) return 1; +#endif /* in->c[1].c */ if (CORE_READ(&out->c1c, &in->c[1].c)) return 1; +#if defined(__clang__) && (__clang_major__ < 10) && (__clang_minor__ < 1) +# warning "clang 9.0 SEGVs on multidimensional arrays, see https://reviews.llvm.org/D69438" +#else /* in->d[0][0].d */ if (CORE_READ(&out->d00d, &in->d[0][0].d)) return 1; +#endif

return 0; }