Comment 0 for bug 1699627

SRU Justification

[Impact]
Some XDP examples such as https://github.com/netoptimizer/prototype-kernel fail on ppc64el at the eBPF verification stage.

[Fix]
This is because CONFIG_HAS_EFFICIENT_UNALIGNED_ACCESS is not set on ppc64el. It is not set because the kernel is being compiled for CPU_POWER7 instead of CPU_POWER8, and we don't have efficient unaligned access on POWER7.

Swap to building for POWER8.

As a bonus, this should make everything a little bit faster.

[Regression Potential]

 - IBM never released any officially supported Power7 LE systems - LE was only ever supported on Power8. Therefore this should not break any systems.

 - Regression potential is also limited to one arch.

 - Artful-next already has this fix and nothing bad has happened there.

[Test]
On a P8 VM with a virtio network card and 2 vcpus:
- get the prototype-kernel repo
- go to the kernel/samples/bpf directory-
- make
- sudo mount -t bpf bpf /sys/fs/bpf/
- sudo ./xdp_ddos01_blacklist --dev enp0s1

Observe that without this patch, we get a long debug splat ending with:

32: (61) r1 = *(u32 *)(r8 +12)
misaligned packet access off 0+18+12 size 4
load_bpf_file: Permission denied

With this patch we don't get that error and the program is successfully verifies and loads. (It still doesn't run - there is other breakage I'm chasing down - but it definitely gets further.)