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SubjectRe: [PATCH bpf-next] bpf: Disable -Wmissing-declarations for globally-linked kfuncs
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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?

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