Re: [PATCH bpf-next 1/4] libbpf: expose map elf section name

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, Mar 1, 2022 at 6:49 PM Delyan Kratunov <delyank@fb.com> wrote:
>
> When generating subskeletons, bpftool needs to know the elf section
> name, as that's the stable identifier that will survive into the final
> linked bpf_object.
>
> This patch adds bpf_map__section_name in symmetry with
> bpf_program__section_name.
>
> Signed-off-by: Delyan Kratunov <delyank@fb.com>
> ---
>  tools/lib/bpf/libbpf.c         | 8 ++++++++
>  tools/lib/bpf/libbpf.h         | 2 ++
>  tools/lib/bpf/libbpf.map       | 5 +++++
>  tools/lib/bpf/libbpf_version.h | 2 +-
>  4 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index be6480e260c4..d20ae8f225ee 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9180,6 +9180,14 @@ const char *bpf_map__name(const struct bpf_map *map)
>         return map->name;
>  }
>
> +const char *bpf_map__section_name(const struct bpf_map *map)
> +{
> +       if (!map)
> +               return NULL;
> +
> +       return map->real_name;
> +}
> +

First, "section_name" here is extremely confusing in the face of
bpf_program__section_name() which returns a very different thing for
BPF program. But I think we shouldn't need to do anything extra here.
Using bpf_map__name() and then bpf_object__find_map_by_name() should
just work (there is real_name special-handling for maps that start
with dot). If that real_name special handling doesn't work for
subskeletons, we should fix that special handling instead of adding a
special getter. But I'll need to look at other patches first and maybe
play around locally with subskeletons.


>  enum bpf_map_type bpf_map__type(const struct bpf_map *map)
>  {
>         return map->def.type;
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index c8d8daad212e..7b66794f1c0a 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -741,6 +741,8 @@ LIBBPF_API LIBBPF_DEPRECATED_SINCE(0, 8, "use appropriate getters or setters ins
>  const struct bpf_map_def *bpf_map__def(const struct bpf_map *map);
>  /* get map name */
>  LIBBPF_API const char *bpf_map__name(const struct bpf_map *map);
> +/* get map ELF section name */
> +LIBBPF_API const char *bpf_map__section_name(const struct bpf_map *map);
>  /* get/set map type */
>  LIBBPF_API enum bpf_map_type bpf_map__type(const struct bpf_map *map);
>  LIBBPF_API int bpf_map__set_type(struct bpf_map *map, enum bpf_map_type type);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 47e70c9058d9..5c85d297d955 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -439,3 +439,8 @@ LIBBPF_0.7.0 {
>                 libbpf_probe_bpf_prog_type;
>                 libbpf_set_memlock_rlim_max;
>  } LIBBPF_0.6.0;
> +
> +LIBBPF_0.8.0 {
> +       global:
> +    bpf_map__section_name;
> +} LIBBPF_0.7.0;
> diff --git a/tools/lib/bpf/libbpf_version.h b/tools/lib/bpf/libbpf_version.h
> index 0fefefc3500b..61f2039404b6 100644
> --- a/tools/lib/bpf/libbpf_version.h
> +++ b/tools/lib/bpf/libbpf_version.h
> @@ -4,6 +4,6 @@
>  #define __LIBBPF_VERSION_H
>
>  #define LIBBPF_MAJOR_VERSION 0
> -#define LIBBPF_MINOR_VERSION 7
> +#define LIBBPF_MINOR_VERSION 8
>
>  #endif /* __LIBBPF_VERSION_H */
> --
> 2.34.1