bpf-next: building samples on s390x

[Ilya Leoshkevich <iii@xxxxxxxxxxxxx>]

Hi all,

I’m trying to build bpf samples on s390x, and I’m getting the following
error:

progs/loop3.c:19:13: error: incomplete definition of type 'struct pt_regs'
                sum += ctx->rax;

I tried to fix that by using `PT_REGS_RC` macro, but:

- `struct pt_regs` is not defined for s390x userspace;
- `PT_REGS_RC` uses `ax` field, which is a part of x86_64 kernel
  version of `struct pt_regs`, whereas `rax` is a part of its userspace
  version.

My question is: which headers should eBPF programs ultimately use:
userspace or kernel? According to my experiments, eBPF samples seem to
use userspace headers and bcc seems to use kernel headers.

Best regards,
Ilya