netdev - Re: [PATCH bpf] libbpf: fix global variable relocation

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Message-ID: <CAEf4BzZ+iEDwCtzzE=JxYQQJ-inkbRx4OOq70ejewUq1-8ahxQ@mail.gmail.com>
Date:   Wed, 27 Nov 2019 12:07:45 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     Andrii Nakryiko <andriin@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf] libbpf: fix global variable relocation

On Wed, Nov 27, 2019 at 10:19 AM Yonghong Song <yhs@...com> wrote:
>
>
>
> On 11/26/19 10:01 PM, Andrii Nakryiko wrote:
> > Similarly to a0d7da26ce86 ("libbpf: Fix call relocation offset calculation
> > bug"), relocations against global variables need to take into account
> > referenced symbol's st_value, which holds offset into a corresponding data
> > section (and, subsequently, offset into internal backing map). For static
> > variables this offset is always zero and data offset is completely described
> > by respective instruction's imm field.
> >
> > Convert a bunch of selftests to global variables. Previously they were relying
> > on `static volatile` trick to ensure Clang doesn't inline static variables,
> > which with global variables is not necessary anymore.
> >
> > Fixes: 393cdfbee809 ("libbpf: Support initialized global variables")
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
>
> LGTM with a few nits below.
>

Good points, I was too laser-focused. Updated in v2, thanks!

> Acked-by: Yonghong Song <yhs@...com>
>
> > ---
> >   tools/lib/bpf/libbpf.c                        | 40 +++++++++----------
> >   .../testing/selftests/bpf/progs/fentry_test.c | 12 +++---
> >   .../selftests/bpf/progs/fexit_bpf2bpf.c       |  6 +--
> >   .../testing/selftests/bpf/progs/fexit_test.c  | 12 +++---
> >   tools/testing/selftests/bpf/progs/test_mmap.c |  4 +-
> >   5 files changed, 35 insertions(+), 39 deletions(-)
> >

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