Re: [PATCH bpf-next] selftests/bpf: fix compilation failure when CONFIG_NET_FOU!=y

[Artem Savkov <asavkov@redhat.com>]

On Fri, Jul 19, 2024 at 10:09:35AM -0700, Alexei Starovoitov wrote:
> On Fri, Jul 19, 2024 at 8:45 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
> >
> > Hi Artem,
> >
> > On 7/18/24 4:31 PM, Artem Savkov wrote:
> > > Without CONFIG_NET_FOU bpf selftests are unable to build because of
> > > missing definitions. Add ___local versions of struct bpf_fou_encap and
> > > enum bpf_fou_encap_type to fix the issue.
> > >
> > > Signed-off-by: Artem Savkov <asavkov@redhat.com>
> >
> > This breaks BPF CI, ptal:
> >
> > https://github.com/kernel-patches/bpf/actions/runs/9999691294/job/27641198557
> >
> >    [...]
> >      CLNG-BPF [test_maps] btf__core_reloc_existence___wrong_field_defs.bpf.o
> >      CLNG-BPF [test_maps] verifier_bswap.bpf.o
> >      CLNG-BPF [test_maps] test_core_reloc_existence.bpf.o
> >      CLNG-BPF [test_maps] test_global_func8.bpf.o
> >      CLNG-BPF [test_maps] verifier_bitfield_write.bpf.o
> >      CLNG-BPF [test_maps] local_storage_bench.bpf.o
> >      CLNG-BPF [test_maps] verifier_runtime_jit.bpf.o
> >      CLNG-BPF [test_maps] test_pkt_access.bpf.o
> >    progs/test_tunnel_kern.c:39:5: error: conflicting types for 'bpf_skb_set_fou_encap'
> >       39 | int bpf_skb_set_fou_encap(struct __sk_buff *skb_ctx,
> >          |     ^
> >    /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/include/vmlinux.h:107714:12: note: previous declaration is here
> >     107714 | extern int bpf_skb_set_fou_encap(struct __sk_buff *skb_ctx, struct bpf_fou_encap *encap, int type) __weak __ksym;
> >            |            ^
> >    progs/test_tunnel_kern.c:41:5: error: conflicting types for 'bpf_skb_get_fou_encap'
> >       41 | int bpf_skb_get_fou_encap(struct __sk_buff *skb_ctx,
> >          |     ^
> >    /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/include/vmlinux.h:107715:12: note: previous declaration is here
> >     107715 | extern int bpf_skb_get_fou_encap(struct __sk_buff *skb_ctx, struct bpf_fou_encap *encap) __weak __ksym;
> >            |            ^
> >      CLNG-BPF [test_maps] verifier_typedef.bpf.o
> >      CLNG-BPF [test_maps] user_ringbuf_fail.bpf.o
> >      CLNG-BPF [test_maps] verifier_map_in_map.bpf.o
> >    progs/test_tunnel_kern.c:782:35: error: incompatible pointer types passing 'struct bpf_fou_encap___local *' to parameter of type 'struct bpf_fou_encap *' [-Werror,-Wincompatible-pointer-types]
> >      782 |         ret = bpf_skb_set_fou_encap(skb, &encap, FOU_BPF_ENCAP_GUE___local);
> >          |                                          ^~~~~~
> >    /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/include/vmlinux.h:107714:83: note: passing argument to parameter 'encap' here
> >     107714 | extern int bpf_skb_set_fou_encap(struct __sk_buff *skb_ctx, struct bpf_fou_encap *encap, int type) __weak __ksym;
> 
> It's a good idea to introduce struct bpf_fou_encap___local
> for !FOU builds, but kfunc signature needs to stay and
> __local variable needs to be type casted to (struct bpf_fou_encap *)
> when calling kfunc.

Casting won't work as the compiler still have no idea about struct
bpf_fou_encap.

I think I'll need to fix this by adding '#define
BPF_NO_KDUNC_PROTOTYPES' to the test. Daniel has done this for other
cases like this in the series introducing bpftool kfunc prototype
dumping (https://lore.kernel.org/all/cover.1718207789.git.dxu@dxuuu.xyz/)

-- 
 Artem