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From:   Song Liu <liu.song.a23@gmail.com>
Date:   Mon, 28 Jan 2019 09:18:45 -0800
Message-ID: <CAPhsuW54z8ao4KOKG9ZjdXus6LTBH2qwAi8LgPFZ_qb_ObKsRg@mail.gmail.com>
Subject: Re: [PATCH] bpf/core.c - silence warning messages
To:     Valdis Kletnieks <valdis.kletnieks@vt.edu>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Networking <netdev@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Sun, Jan 27, 2019 at 8:43 PM <valdis.kletnieks@vt.edu> wrote:
>
> Compiling kernel/bpf/core.c with W=1 causes a flood of warnings:
>
> kernel/bpf/core.c:1198:65: warning: initialized field overwritten [-Woverride-init]
>  1198 | #define BPF_INSN_3_TBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = true
>       |                                                                 ^~~~
> kernel/bpf/core.c:1087:2: note: in expansion of macro 'BPF_INSN_3_TBL'
>  1087 |  INSN_3(ALU, ADD,  X),   \
>       |  ^~~~~~
> kernel/bpf/core.c:1202:3: note: in expansion of macro 'BPF_INSN_MAP'
>  1202 |   BPF_INSN_MAP(BPF_INSN_2_TBL, BPF_INSN_3_TBL),
>       |   ^~~~~~~~~~~~
> kernel/bpf/core.c:1198:65: note: (near initialization for 'public_insntable[12]')
>  1198 | #define BPF_INSN_3_TBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = true
>       |                                                                 ^~~~
> kernel/bpf/core.c:1087:2: note: in expansion of macro 'BPF_INSN_3_TBL'
>  1087 |  INSN_3(ALU, ADD,  X),   \
>       |  ^~~~~~
> kernel/bpf/core.c:1202:3: note: in expansion of macro 'BPF_INSN_MAP'
>  1202 |   BPF_INSN_MAP(BPF_INSN_2_TBL, BPF_INSN_3_TBL),
>       |   ^~~~~~~~~~~~
>
> 98 copies of the above.
>
> The attached patch silences the warnings, because we *know* we're overwriting
> the default initializer. That leaves bpf/core.c with only 6 other warnings,
> which become more visible in comparison.

My concern is that this will also mute the warning for other parts of
bpf/core.c.

Maybe we should move bpf_opcode_in_insntable() to a separate file, and mute
warning for that file?

Daniel and Alexei, what do you think?

Thanks,
Song


>
> Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
>
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index 4c2fa3ac56f6..2606665f2cb5 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -21,3 +21,4 @@ obj-$(CONFIG_CGROUP_BPF) += cgroup.o
>  ifeq ($(CONFIG_INET),y)
>  obj-$(CONFIG_BPF_SYSCALL) += reuseport_array.o
>  endif
> +CFLAGS_core.o          += $(call cc-disable-warning, override-init)
>