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

[Andrii Nakryiko]

On Mon, May 23, 2022 at 1:26 PM Michael Mullin <masmullin@xxxxxxxxx> 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@xxxxxxxxx>
> ---
>  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
>