Re: selftests/bpf - Error: failed to open BPF object file: Endian mismatch

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 02/04/2021 à 09:48, Christophe Leroy a écrit :
> Hello,
> 
> I'm having hard time cross-building bpf selftests on an x86 for a powerpc target.
> 
> [root@PC-server-ldb bpf]# make CROSS_COMPILE=ppc-linux- ARCH=powerpc V=1
> /root/gen_ldb/linux-powerpc/tools/testing/selftests/bpf/host-tools/sbin/bpftool gen skeleton 
> /root/gen_ldb/linux-powerpc/tools/testing/selftests/bpf/atomic_bounds.o > 
> /root/gen_ldb/linux-powerpc/tools/testing/selftests/bpf/atomic_bounds.skel.h
> libbpf: elf: endianness mismatch in atomic_bounds.
> Error: failed to open BPF object file: Endian mismatch
> 
> [root@PC-server-ldb bpf]# file atomic_bounds.o
> atomic_bounds.o: ELF 64-bit MSB relocatable, eBPF, version 1 (SYSV), with debug_info, not stripped
> 
> Seems like the just-built host bpftool doesn't take into account target's endianness.
> 
> I see the patch https://github.com/torvalds/linux/commit/313e7f6f ("selftest/bpf: Use -m{little, 
> big}-endian for clang") in bpf selftest to enable cross-compilation, but it seems it is not enough.
> 
> What should I do to get bpftool work with the target's endianness ?
> 

I also see https://github.com/torvalds/linux/commit/8859b0da ("tools/bpftool: Fix cross-build") but 
that commit doesn't seem to address endianness difference between the host and the target.

Christophe