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Subject: Re: [PATCH] bpf: fix build warning - missing prototype
To:     Jean-Philippe Menil <jpmenil@gmail.com>
CC:     <netdev@vger.kernel.org>, <kernel-janitors@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        Andrii Nakryiko <andriin@fb.com>, <bpf@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
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From:   Yonghong Song <yhs@fb.com>
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Date:   Mon, 23 Mar 2020 07:52:00 -0700
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On 3/23/20 12:42 AM, Jean-Philippe Menil wrote:
> On 22/03/20 at 10:32pm, Yonghong Song wrote:
>>
>>
>> On 3/22/20 7:08 AM, Jean-Philippe Menil wrote:
>>> Fix build warning when building net/bpf/test_run.o with W=1 due
>>> to missing prototype for bpf_fentry_test{1..6}.
>>>
>>> These functions are only used in test_run.c so just make them static.
>>> Therefore inline keyword should sit between storage class and type.
>>
>> This won't work. These functions are intentionally global functions
>> so that their definitions will be in vmlinux BTF and fentry/fexit kernel
>> selftests can run against them.
>>
>> See file 
>> linux/tools/testing/selftests/bpf/progs/{fentry_test.c,fexit_test.c}.
>>
> 
> I can see now, thanks for the pointer.
> I totally missed that.
> 
> So, in order to fix the warnings, better to declare the prototypes?
> (compiling with W=1 may be a bit unusual).

Right, you can add prototypes in the same file (test_run.c) to silence 
the warning.

> 
>>>
>>> Signed-off-by: Jean-Philippe Menil <jpmenil@gmail.com>
>>> ---
>>>  net/bpf/test_run.c | 12 ++++++------
>>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
>>> index d555c0d8657d..c0dcd29f682c 100644
>>> --- a/net/bpf/test_run.c
>>> +++ b/net/bpf/test_run.c
>>> @@ -113,32 +113,32 @@ static int bpf_test_finish(const union bpf_attr 
>>> *kattr,
>>>   * architecture dependent calling conventions. 7+ can be supported 
>>> in the
>>>   * future.
>>>   */
>>> -int noinline bpf_fentry_test1(int a)
>>> +static noinline int bpf_fentry_test1(int a)
>>>  {
>>>      return a + 1;
>>>  }
>>> -int noinline bpf_fentry_test2(int a, u64 b)
>>> +static noinline int bpf_fentry_test2(int a, u64 b)
>>>  {
>>>      return a + b;
>>>  }
>>> -int noinline bpf_fentry_test3(char a, int b, u64 c)
>>> +static noinline int bpf_fentry_test3(char a, int b, u64 c)
>>>  {
>>>      return a + b + c;
>>>  }
>>> -int noinline bpf_fentry_test4(void *a, char b, int c, u64 d)
>>> +static noinline int bpf_fentry_test4(void *a, char b, int c, u64 d)
>>>  {
>>>      return (long)a + b + c + d;
>>>  }
>>> -int noinline bpf_fentry_test5(u64 a, void *b, short c, int d, u64 e)
>>> +static noinline int bpf_fentry_test5(u64 a, void *b, short c, int d, 
>>> u64 e)
>>>  {
>>>      return a + (long)b + c + d + e;
>>>  }
>>> -int noinline bpf_fentry_test6(u64 a, void *b, short c, int d, void 
>>> *e, u64 f)
>>> +static noinline int bpf_fentry_test6(u64 a, void *b, short c, int d, 
>>> void *e, u64 f)
>>>  {
>>>      return a + (long)b + c + d + (long)e + f;
>>>  }
>>>
>