Re: [PATCH v2 bpf-next 14/20] libbpf: Recognize __arena global varaibles.

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Thu, Feb 15, 2024 at 3:22 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
>  {
> @@ -2835,6 +2819,33 @@ static int
> bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
>              return err;
>      }
>
> +    for (i = 0; i < obj->nr_maps; i++) {
> +        struct bpf_map *map = &obj->maps[i];
> +
> +        if (map->def.type != BPF_MAP_TYPE_ARENA)
> +            continue;
> +
> +        if (obj->arena_map) {
> +            pr_warn("map '%s': only single ARENA map is supported
> (map '%s' is also ARENA)\n",
> +                map->name, obj->arena_map->name);
> +            return -EINVAL;
> +        }
> +        obj->arena_map = map;
> +
> +        if (obj->efile.arena_data) {
> +            err = init_arena_map_data(obj, map, ARENA_SEC,
> obj->efile.arena_data_shndx,
> +                          obj->efile.arena_data->d_buf,
> +                          obj->efile.arena_data->d_size);
> +            if (err)
> +                return err;
> +        }
> +    }
> +    if (obj->efile.arena_data && !obj->arena_map) {
> +        pr_warn("elf: sec '%s': to use global __arena variables the
> ARENA map should be explicitly declared in SEC(\".maps\")\n",
> +            ARENA_SEC);
> +        return -ENOENT;
> +    }
> +
>      return 0;
>  }
>
> @@ -3699,9 +3710,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
>                  obj->efile.st_ops_link_data = data;
>                  obj->efile.st_ops_link_shndx = idx;
>              } else if (strcmp(name, ARENA_SEC) == 0) {
> -                sec_desc->sec_type = SEC_ARENA;
> -                sec_desc->shdr = sh;
> -                sec_desc->data = data;
> +                obj->efile.arena_data = data;
> +                obj->efile.arena_data_shndx = idx;

I see. So these two are sort-of main tricks.
Special case ARENA_SEC like ".maps" and then look for this
obj level map in the right spots.
The special case around bpf_map__[set_]initial_value kind break
the layering with:
if (map->def.type == BPF_MAP_TYPE_ARENA)
  actual_sz = map->obj->arena_data_sz;
but no big deal.

How do you want me to squash the patches?
Keep "rename is_internal_mmapable_map into is_mmapable_map" patch as-is
and then squash mine and your 2nd and 3rd?