linux-kernel - Re: [PATCH] bpf: fix build warning

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Date:   Mon, 23 Mar 2020 08:42:47 +0100
From:   Jean-Philippe Menil <jpmenil@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     netdev@...r.kernel.org, kernel-janitors@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        Andrii Nakryiko <andriin@...com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: fix build warning - missing prototype

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).

>>
>>Signed-off-by: Jean-Philippe Menil <jpmenil@...il.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;
>>  }
>>

-- 
Jean-Philippe Menil