netdev - Re: [PATCH bpf-next 3/4] bpftool: Fix incorrect return in generated detach helper

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Date:   Mon, 25 Apr 2022 23:47:29 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 3/4] bpftool: Fix incorrect return in generated
 detach helper

On Sat, Apr 23, 2022 at 7:02 AM Yafang Shao <laoar.shao@...il.com> wrote:
>
> There is no return value of bpf_object__detach_skeleton(), so we'd
> better not return it, that is formal.
>
> Fixes: 5dc7a8b21144 ("bpftool, selftests/bpf: Embed object file inside skeleton")
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> ---
>  tools/bpf/bpftool/gen.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 7678af364793..8f76d8d9996c 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -1171,7 +1171,7 @@ static int do_skeleton(int argc, char **argv)
>                 static inline void                                          \n\
>                 %1$s__detach(struct %1$s *obj)                              \n\
>                 {                                                           \n\
> -                       return bpf_object__detach_skeleton(obj->skeleton);  \n\
> +                       bpf_object__detach_skeleton(obj->skeleton);         \n\

It's not incorrect to return the result of void-returning function in
another void-returning function. C compiler allows this and we rely on
this property very explicitly in macros like BPF_PROG and BPF_KPROBE.
So if anything, it's not a fix, at best improvement, but even then
quite optional.


>                 }                                                           \n\
>                 ",
>                 obj_name
> --
> 2.17.1
>