Re: [PATCH bpf-next] selftests/bpf: Add a test for attaching a bpf fentry/fexit trace to an XDP program

["Eelco Chaudron" <echaudro@xxxxxxxxxx>]

On 20 Dec 2019, at 0:02, Andrii Nakryiko wrote:

> On Thu, Dec 19, 2019 at 3:04 AM Eelco Chaudron <echaudro@xxxxxxxxxx> 
> wrote:
> > Add a test that will attach a FENTRY and FEXIT program to the XDP 
> > test
> > program. It will also verify data from the XDP context on FENTRY and
> > verifies the return code on exit.
> >
> > Signed-off-by: Eelco Chaudron <echaudro@xxxxxxxxxx>
> > ---
> >  .../testing/selftests/bpf/prog_tests/xdp_bpf2bpf.c |   95 
> > ++++++++++++++++++++
> >  .../testing/selftests/bpf/progs/test_xdp_bpf2bpf.c |   44 +++++++++
> >  2 files changed, 139 insertions(+)
> >  create mode 100644 
> > tools/testing/selftests/bpf/prog_tests/xdp_bpf2bpf.c
> >  create mode 100644 
> > tools/testing/selftests/bpf/progs/test_xdp_bpf2bpf.c
>
> [...]

Thanks for the review, updated my kernel to the latest bfp-next, but now 
I get the following build issue for the test suite:

   GEN-SKEL [test_progs] loop3.skel.h
   GEN-SKEL [test_progs] test_skeleton.skel.h
libbpf: failed to find BTF for extern 'CONFIG_BPF_SYSCALL': -2
Error: failed to open BPF object file: 0
make: *** [Makefile:333: 
/data/linux_kernel/tools/testing/selftests/bpf/test_skeleton.skel.h] 
Error 255
make: *** Deleting file 
'/data/linux_kernel/tools/testing/selftests/bpf/test_skeleton.skel.h'

Verified, and I still have all the correct config and CLANG version. 
Something else I need to update?
I have pahole v1.15 in my search path…

> > +       /* Load XDP program to introspect */
> > +       err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj, &prog_fd);
>
> Please use BPF skeleton for this test. It will make it significantly
> shorter and clearer. See other fentry_fexit selftest for example.
>
> > +       if (CHECK_FAIL(err))
> > +               return;
> > +
>
> [...]
>
> > +
> > +static volatile __u64 test_result_fentry;
>
> no need for static volatile anymore, just use global var
>
> > +BPF_TRACE_1("fentry/_xdp_tx_iptunnel", trace_on_entry,
> > +           struct xdp_buff *, xdp)
> > +{
> > +       test_result_fentry = xdp->rxq->dev->ifindex;
> > +       return 0;
> > +}
> > +
> > +static volatile __u64 test_result_fexit;
>
> same here
>
> > +BPF_TRACE_2("fexit/_xdp_tx_iptunnel", trace_on_exit,
> > +           struct xdp_buff*, xdp, int, ret)
> > +{
> > +       test_result_fexit = ret;
> > +       return 0;
> > +}