Re: [PATCH v3 bpf-next 18/18] selftests/bpf: Add a test for attaching BPF prog to another BPF prog and subprog

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Sun, Nov 10, 2019 at 09:04:58AM -0800, Andrii Nakryiko wrote:
> On Thu, Nov 7, 2019 at 10:43 PM Alexei Starovoitov <ast@kernel.org> wrote:
> >
> > Add a test that attaches one FEXIT program to main sched_cls networking program
> > and two other FEXIT programs to subprograms. All three tracing programs
> > access return values and skb->len of networking program and subprograms.
> >
> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > ---
> 
> Acked-by: Andrii Nakryiko <andriin@fb.com>
> 
> >  .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  | 76 ++++++++++++++++
> >  .../selftests/bpf/progs/fexit_bpf2bpf.c       | 91 +++++++++++++++++++
> >  2 files changed, 167 insertions(+)
> >  create mode 100644 tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c
> >
> 
> [...]
> 
> > +SEC("fexit/test_pkt_access_subprog2")
> > +int test_subprog2(struct args_subprog2 *ctx)
> > +{
> > +       struct sk_buff *skb = (void *)ctx->args[0];
> > +       __u64 ret;
> > +       int len;
> > +
> > +       bpf_probe_read(&len, sizeof(len),
> > +                      __builtin_preserve_access_index(&skb->len));
> 
> nit: we have bpf_core_read() for this, but I suspect you may have
> wanted __builtin spelled out explicitly

exactly. it should have been bpf_probe_read_kernel though. will fix.