netdev - Re: [PATCH v2 bpf-next 2/2] selftests/bpf: add byte swapping selftest

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Message-ID: <CAEf4BzZsEJDAzeY6vJG5873Y4nnB9b+NrSiSzAHQWATMKfnO_w@mail.gmail.com>
Date:   Tue, 30 Jun 2020 08:18:06 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 2/2] selftests/bpf: add byte swapping selftest

On Tue, Jun 30, 2020 at 7:09 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 6/30/20 8:07 AM, Andrii Nakryiko wrote:
> > Add simple selftest validating byte swap built-ins and compile-time macros.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---
> >   .../testing/selftests/bpf/prog_tests/endian.c | 53 +++++++++++++++++++
> >   .../testing/selftests/bpf/progs/test_endian.c | 37 +++++++++++++
> >   2 files changed, 90 insertions(+)
> >   create mode 100644 tools/testing/selftests/bpf/prog_tests/endian.c
> >   create mode 100644 tools/testing/selftests/bpf/progs/test_endian.c
>
> This fails the build for me with:
>
> [...]
>    GEN-SKEL [test_progs] tailcall3.skel.h
>    GEN-SKEL [test_progs] test_endian.skel.h
> libbpf: invalid relo for 'const16' in special section 0xfff2; forgot to initialize global var?..
> Error: failed to open BPF object file: 0
> Makefile:372: recipe for target '/root/bpf-next/tools/testing/selftests/bpf/test_endian.skel.h' failed
> make: *** [/root/bpf-next/tools/testing/selftests/bpf/test_endian.skel.h] Error 255
> make: *** Deleting file '/root/bpf-next/tools/testing/selftests/bpf/test_endian.skel.h'

Interesting. You must have a bit of an older Clang. I noticed people
submit code without explicit initialization of global variables, which
is ok now, because I think Clang doesn't emit it into the COM section
anymore. I'm surprised you don't get other compilation errors.

But regardless, I'll respin with explicit zero-initialization to fix this.