linux-kernel - Re: [PATCH bpf-next] bpf: fix 'dubious one-bit signed bitfield' warnings

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Message-ID: <428689f2-ad91-e1b4-64c5-c1c4802e2cbe@tessares.net>
Date:   Sun, 10 Jul 2022 22:19:03 +0200
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Yonghong Song <yhs@...com>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Eduard Zingerman <eddyz87@...il.com>
Cc:     mptcp@...ts.linux.dev, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: fix 'dubious one-bit signed bitfield'
 warnings

Hi Yonghong,

Thank you for the review!

On 10/07/2022 18:59, Yonghong Song wrote:> On 7/10/22 1:35 AM, Matthieu
Baerts wrote:
>> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
>> index 81b19669efba..2ac424641cc3 100644
>> --- a/include/linux/bpf_verifier.h
>> +++ b/include/linux/bpf_verifier.h
>> @@ -345,10 +345,10 @@ struct bpf_verifier_state_list {
>>   };
>>     struct bpf_loop_inline_state {
>> -    int initialized:1; /* set to true upon first entry */
>> -    int fit_for_inline:1; /* true if callback function is the same
>> -                   * at each call and flags are always zero
>> -                   */
>> +    bool initialized; /* set to true upon first entry */
>> +    bool fit_for_inline; /* true if callback function is the same
>> +                  * at each call and flags are always zero
>> +                  */
> 
> I think changing 'int' to 'unsigned' is a better alternative for
> potentially adding more bitfields in the future. This is also a pattern
> for many other kernel data structures.

There was room, I was not sure if it would be OK but I saw 'bool' were
often used in structures from this bpf_verifier.h file.

I can of course switch to an unsigned one. I would have picked 'u8' when
looking at the structures around but any preferences from you?
'unsigned', 'unsigned int', 'u8', 'u32'?

Cheers,
Matt
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