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Date:   Wed, 24 May 2023 15:23:24 +0200
From:   "Arnd Bergmann" <arnd@arndb.de>
To:     "Yonghong Song" <yhs@meta.com>, "Arnd Bergmann" <arnd@kernel.org>,
        "Alexei Starovoitov" <ast@kernel.org>,
        "Daniel Borkmann" <daniel@iogearbox.net>,
        "Andrii Nakryiko" <andrii@kernel.org>
Cc:     "John Fastabend" <john.fastabend@gmail.com>,
        "Martin KaFai Lau" <martin.lau@linux.dev>,
        "Song Liu" <song@kernel.org>, "Yonghong Song" <yhs@fb.com>,
        "KP Singh" <kpsingh@kernel.org>,
        "Stanislav Fomichev" <sdf@google.com>,
        "Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>,
        "Jason A . Donenfeld" <Jason@zx2c4.com>, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] [v2] bpf: hide unused bpf_patch_call_args
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On Wed, May 24, 2023, at 05:05, Yonghong Song wrote:
> On 5/23/23 12:43 PM, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>> 
>> This function has no callers and no declaration when CONFIG_BPF_JIT_ALWAYS_ON
>> is enabled:
>> 
>> kernel/bpf/core.c:2075:6: error: no previous prototype for 'bpf_patch_call_args' [-Werror=missing-prototypes]
>
> If CONFIG_BPF_JIT_ALWAYS_ON is enabled, the definition of
> bpf_patch_call_args should be invisible. Maybe I missed something.
> Could you list *ALL& bpf related config options in your setup
> so people can reproduce you above error messages?

Sorry, my mistake. I've reworded the changelog now to fix this:

| This function is only used when CONFIG_BPF_JIT_ALWAYS_ON is disabled,
| but CONFIG_BPF_SYSCALL is enabled. When both are turned off, the
| prototype is missing but the unused function is still compiled,
| as seen from this W=1 warning:
| 
| kernel/bpf/core.c:2075:6: error: no previous prototype for 'bpf_patch_call_args' [-Werror=missing-prototypes]
| 
| Add a matching #ifdef for the definition to leave it out.

If this makes sense now, I'll send out a v3.

      Arnd