linux-kernel - Re: [PATCH] bpftool: mmaped fields missing map structure in generated skeletons

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Message-ID: <CAEf4BzaecP2XkzftmH7GeeTfj1E+pv=20=L4ztrxe4-JU7MuUw@mail.gmail.com>
Date:   Mon, 23 May 2022 15:02:31 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Michael Mullin <masmullin@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai 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>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpftool: mmaped fields missing map structure in generated skeletons

On Mon, May 23, 2022 at 1:26 PM Michael Mullin <masmullin@...il.com> wrote:
>
> When generating a skeleton which has an mmaped map field, bpftool's
> output is missing the map structure.  This causes a compile break when
> the generated skeleton is compiled as the field belongs to the internal
> struct maps, not directly to the obj.
>
> Signed-off-by: Michael Mullin <masmullin@...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 f158dc1c2149..b49293795ba0 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -853,7 +853,7 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
>                         i, bpf_map__name(map), i, ident);
>                 /* memory-mapped internal maps */
>                 if (mmaped && is_internal_mmapable_map(map, ident, sizeof(ident))) {
> -                       printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n",
> +                       printf("\ts->maps[%zu].mmaped = (void **)&obj->maps.%s;\n",

That's not right. maps.my_map is struct bpf_map *, but mmaped is
supposed to be a blob of memory that is memory-mapped into map.

Can you elaborate on how you trigger that compilation error with a
small example?

>                                 i, ident);
>                 }
>                 i++;
> --
> 2.36.1
>