netdev - Re: [PATCH v2 bpf-next 06/11] libbpf: add BPF static linker APIs

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Message-ID: <CAEf4BzbCiMkQazSe2hky=Jx6QXZiZ2jyf+AuzMJEyAv+_B7vug@mail.gmail.com>
Date:   Mon, 7 Jun 2021 21:08:36 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Tom Stellard <tstellar@...hat.com>
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...com>, bpf <bpf@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 06/11] libbpf: add BPF static linker APIs

On Mon, Jun 7, 2021 at 7:41 PM Tom Stellard <tstellar@...hat.com> wrote:
>
> On 6/7/21 5:25 PM, Andrii Nakryiko wrote:
> > On Mon, Jun 7, 2021 at 4:12 PM Tom Stellard <tstellar@...hat.com> wrote:
> >>
> >>
> >> Hi,
> >>
> >>> +                               } else {
> >>> +                                       pr_warn("relocation against STT_SECTION in non-exec section is not supported!\n");
> >>> +                                       return -EINVAL;
> >>> +                               }
> >>
> >> Kernel build of commit 324c92e5e0ee are failing for me with this error
> >> message:
> >>
> >> /builddir/build/BUILD/kernel-5.13-rc4-61-g324c92e5e0ee/linux-5.13.0-0.rc4.20210603git324c92e5e0ee.35.fc35.x86_64/tools/bpf/bpftool/bpftool gen object /builddir/build/BUILD/kernel-5.13-rc4-61-g324c92e5e0ee/linux-5.13.0-0.rc4.20210603git324c92e5e0ee.35.fc35.x86_64/tools/testing/selftests/bpf/bind_perm.linked1.o /builddir/build/BUILD/kernel-5.13-rc4-61-g324c92e5e0ee/linux-5.13.0-0.rc4.20210603git324c92e5e0ee.35.fc35.x86_64/tools/testing/selftests/bpf/bind_perm.o
> >> libbpf: relocation against STT_SECTION in non-exec section is not supported!
> >>
> >> What information can I provide to help debug this failure?
> >
> > Can you please send that bind_perm.o file? Also what's your `clang
> > --version` output?
> >
>
> clang version 12.0.0 (Fedora 12.0.0-2.fc35)
>
> >> I suspect this might be due to Clang commit 6a2ea84600ba ("BPF: Add
> >> more relocation kinds"), but I get a different error on 324c92e5e0ee.
> >> So meanwhile you might try applying 9f0c317f6aa1 ("libbpf: Add support
> >> for new llvm bpf relocations") from bpf-next/master and check if that
> >> helps. But please do share bind_perm.o, just to double-check what's
> >> going on.
> >>
>
> Here is bind_perm.o: https://fedorapeople.org/~tstellar/bind_perm.o
>

So somehow you end up with .eh_frame section in BPF object file, which
shouldn't ever happen. So there must be something that you are doing
differently (compiler flags or something else) that makes Clang
produce .eh_frame. So we need to figure out why .eh_frame gets
generated. Not sure how, but maybe you have some ideas of what might
be different about your build.

> Thanks,
> Tom
>
> >>
> >>>
> >>> Thanks,
> >>> Tom
> >>>
> >>
> >
>