From: Yonghong Song <yonghong.song@linux.dev>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: David Vernet <void@manifault.com>, bpf <bpf@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Kernel Team <kernel-team@meta.com>,
kernel test robot <lkp@intel.com>
Subject: Re: [PATCH bpf-next] bpf: Disable -Wmissing-declarations for globally-linked kfuncs
Date: Wed, 16 Aug 2023 23:08:29 -0700 [thread overview]
Message-ID: <42d6b829-ab97-2b81-de2c-7551da13f913@linux.dev> (raw)
In-Reply-To: <CAADnVQKtWkPWMG+F-Tkf3YXeMnC=Xwi8GA5xJMaqi725tgHSTw@mail.gmail.com>
On 8/16/23 8:48 PM, Alexei Starovoitov wrote:
> On Wed, Aug 16, 2023 at 8:38 PM Yonghong Song <yonghong.song@linux.dev> wrote:
>>
>>
>>
>> On 8/16/23 8:06 AM, David Vernet wrote:
>>> We recently got an lkp warning about missing declarations, as in e.g.
>>> [0]. This warning is largely redundant with -Wmissing-prototypes, which
>>> we already disable for kfuncs that have global linkage and are meant to
>>> be exported in BTF, and called from BPF programs. Let's also disable
>>> -Wmissing-declarations for kfuncs. For what it's worth, I wasn't able to
>>> reproduce the warning even on W <= 3, so I can't actually be 100% sure
>>> this fixes the issue.
>>>
>>> [0]: https://lore.kernel.org/all/202308162115.Hn23vv3n-lkp@intel.com/
>>
>> Okay, I just got a similar email to [0] which complains
>> bpf_obj_new_impl, ..., bpf_cast_to_kern_ctx
>> missing declarations.
>>
>> In the email, the used compiler is
>> compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
>>
>> Unfortunately, I did not have gcc-7 to verify this.
>> Also, what is the minimum gcc version kernel supports? 5.1?
>
> pahole and BTF might be broken in such old GCC too.
> Maybe we should add:
> config BPF_SYSCALL
> depends on GCC_VERSION >= 90000 || CLANG_VERSION >= 130000
Do you remember what kind of issues pahole/BTF have for
< 9.0 gcc and < 13.0 clang?
prev parent reply other threads:[~2023-08-17 6:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-16 15:06 [PATCH bpf-next] bpf: Disable -Wmissing-declarations for globally-linked kfuncs David Vernet
2023-08-17 3:38 ` Yonghong Song
2023-08-17 3:48 ` Alexei Starovoitov
2023-08-17 4:01 ` David Vernet
2023-08-17 14:35 ` Daniel Borkmann
2023-08-17 14:45 ` Anton Protopopov
2023-08-17 6:08 ` Yonghong Song [this message]
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