netdev - Re: [PATCH] bpf/core.c - silence warning messages

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Date:   Tue, 29 Jan 2019 00:22:26 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Song Liu <liu.song.a23@...il.com>,
        Valdis Kletnieks <valdis.kletnieks@...edu>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf/core.c - silence warning messages

On 01/28/2019 06:18 PM, Song Liu wrote:
> On Sun, Jan 27, 2019 at 8:43 PM <valdis.kletnieks@...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.

Agree, valid concern.

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

I think moving in separate file would be overkill, imho. However, lets get
the kdoc and prototype warning fixed.

Thanks,
Daniel