linux-kernel - Re: [PATCH 1/2] [v2] bpf: hide unused bpf_patch_call

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Date:   Tue, 23 May 2023 20:05:58 -0700
From:   Yonghong Song <yhs@...a.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] [v2] bpf: hide unused bpf_patch_call_args



On 5/23/23 12:43 PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.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?

> 
> Hide the definition as well.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2: change indentation to align arguments better. Still not great
> as the line is just too long
> ---
>   kernel/bpf/core.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 7421487422d4..0926714641eb 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2064,14 +2064,16 @@ EVAL4(PROG_NAME_LIST, 416, 448, 480, 512)
>   };
>   #undef PROG_NAME_LIST
>   #define PROG_NAME_LIST(stack_size) PROG_NAME_ARGS(stack_size),
> -static u64 (*interpreters_args[])(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5,
> -				  const struct bpf_insn *insn) = {
> +static __maybe_unused
> +u64 (*interpreters_args[])(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5,
> +			   const struct bpf_insn *insn) = {
>   EVAL6(PROG_NAME_LIST, 32, 64, 96, 128, 160, 192)
>   EVAL6(PROG_NAME_LIST, 224, 256, 288, 320, 352, 384)
>   EVAL4(PROG_NAME_LIST, 416, 448, 480, 512)
>   };
>   #undef PROG_NAME_LIST
>   
> +#ifdef CONFIG_BPF_SYSCALL
>   void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth)
>   {
>   	stack_depth = max_t(u32, stack_depth, 1);
> @@ -2080,6 +2082,7 @@ void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth)
>   		__bpf_call_base_args;
>   	insn->code = BPF_JMP | BPF_CALL_ARGS;
>   }
> +#endif
>   
>   #else
>   static unsigned int __bpf_prog_ret0_warn(const void *ctx,