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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Date:   Mon, 23 Dec 2019 13:53:59 +0100
From:   "Eelco Chaudron" <echaudro@...hat.com>
To:     "Andrii Nakryiko" <andrii.nakryiko@...il.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 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
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;
>> +}
>>