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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Thu, 28 Apr 2022 09:22:53 -0700
Message-ID: <CAEf4BzZDmOWy+q_sqW7ziSjdqgZ9c7hGDkD4TKjAQ9dzN0_-ug@mail.gmail.com>
Subject: Re: [PATCH] libbpf: fix returnvar.cocci warnings
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     kernel test robot <lkp@intel.com>,
        Julia Lawall <julia.lawall@inria.fr>,
        Andrii Nakryiko <andrii@kernel.org>, kbuild-all@lists.01.org,
        Linux Memory Management List <linux-mm@kvack.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
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On Wed, Apr 27, 2022 at 9:07 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Apr 27, 2022 at 1:04 AM kernel test robot <lkp@intel.com> wrote:
> >
> > From: kernel test robot <lkp@intel.com>
> >
> > tools/lib/bpf/relo_core.c:1064:8-11: Unneeded variable: "len". Return "0" on line 1086
> >
> >
> >  Remove unneeded variable used to store return value.
> >
> > Generated by: scripts/coccinelle/misc/returnvar.cocci
> >
> > Fixes: b58af63aab11 ("libbpf: Refactor CO-RE relo human description formatting routine")
> > CC: Andrii Nakryiko <andrii@kernel.org>
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: kernel test robot <lkp@intel.com>
> > ---
> >
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > head:   f02ac5c95dfd45d2f50ecc68d79177de326c668c
> > commit: b58af63aab11e4ae00fe96de9505759cfdde8ee9 [6746/7265] libbpf: Refactor CO-RE relo human description formatting routine
> > :::::: branch date: 2 hours ago
> > :::::: commit date: 9 hours ago
> >
> >  tools/lib/bpf/relo_core.c |   10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > --- a/tools/lib/bpf/relo_core.c
> > +++ b/tools/lib/bpf/relo_core.c
> > @@ -1061,7 +1061,7 @@ static int bpf_core_format_spec(char *bu
> >         const struct btf_enum *e;
> >         const char *s;
> >         __u32 type_id;
> > -       int i, len = 0;
> > +       int i;
> >
> >  #define append_buf(fmt, args...)                               \
> >         ({                                                      \
> > @@ -1083,7 +1083,7 @@ static int bpf_core_format_spec(char *bu
> >                    type_id, btf_kind_str(t), str_is_empty(s) ? "<anon>" : s);
> >
> >         if (core_relo_is_type_based(spec->relo_kind))
> > -               return len;
> > +               return 0;
>
> cocci is wrong.
> It missed append_buf() macro.

Should be irrelevant once [0] lands. It makes use of that return value directly.

  [0] https://patchwork.kernel.org/project/netdevbpf/patch/20220428041523.4089853-2-andrii@kernel.org/

>
> Please fix cocci so we don't have to manually deal with
> broken patches like this one.