Re: [PATCH bpf-next v3 1/3] selftests/bpf: Allow building with extra flags

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Viktor Malik <vmalik@redhat.com> writes:

> In order to specify extra compilation or linking flags to BPF selftests,
> it is possible to set EXTRA_CFLAGS and EXTRA_LDFLAGS from the command
> line. The problem is that they are not propagated to sub-make calls
> (runqslower, bpftool, libbpf) and in the better case are not applied, in
> the worse case cause the entire build fail.
>
> Propagate EXTRA_CFLAGS and EXTRA_LDFLAGS to the sub-makes.
>
> This, for instance, allows to build selftests as PIE with
>
>     $ make EXTRA_CFLAGS='-fPIE' EXTRA_LDFLAGS='-pie'
>
> Without this change, the command would fail because libbpf.a would not
> be built with -fPIE and other PIE binaries would not link against it.
>
> The only problem is that we have to explicitly provide empty
> EXTRA_CFLAGS='' and EXTRA_LDFLAGS='' to the builds of kernel modules as
> we don't want to build modules with flags used for userspace (the above
> example would fail as kernel doesn't support PIE).
>
> Signed-off-by: Viktor Malik <vmalik@redhat.com>

That last bit is a bit ugly, but I couldn't think of a better way of
doing it, so with that:

Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>