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

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Message-ID: <CAEf4BzYppnG--OnEo0Ft9+pcvJ6+mY47XzY5F+r+2p3+FeUQcA@mail.gmail.com>
Date:   Mon, 23 Dec 2019 09:57:19 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Eelco Chaudron <echaudro@...hat.com>
Cc:     bpf <bpf@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next] selftests/bpf: Add a test for attaching a bpf
 fentry/fexit trace to an XDP program

On Mon, Dec 23, 2019 at 4:54 AM Eelco Chaudron <echaudro@...hat.com> wrote:
>
>
>
> On 20 Dec 2019, at 0:02, Andrii Nakryiko wrote:
>
> > On Thu, Dec 19, 2019 at 3:04 AM Eelco Chaudron <echaudro@...hat.com>
> > 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@...hat.com>
> >> ---
> >>  .../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

This looks like you have Clang without BTF types for extern. Can you
try pull the very latest Clang/LLVM and try again? The latest commit
you should have is e3d8ee35e4ad ("reland "[DebugInfo] Support to emit
debugInfo for extern variables"").

> 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;
> >> +}
> >>
>