netdev - Re: [PATCH bpf-next 5/8] libbpf: split initialization and loading of BTF

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Date:   Sat, 15 Jun 2019 14:21:14 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 5/8] libbpf: split initialization and loading of BTF

On Mon, Jun 10, 2019 at 9:49 PM Andrii Nakryiko <andriin@...com> wrote:
>
> Libbpf does sanitization of BTF before loading it into kernel, if kernel
> doesn't support some of newer BTF features. This removes some of the
> important information from BTF (e.g., DATASEC and VAR description),
> which will be used for map construction. This patch splits BTF
> processing into initialization step, in which BTF is initialized from
> ELF and all the original data is still preserved; and
> sanitization/loading step, which ensures that BTF is safe to load into
> kernel. This allows to use full BTF information to construct maps, while
> still loading valid BTF into older kernels.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  tools/lib/bpf/libbpf.c | 34 ++++++++++++++++++++++++----------
>  1 file changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 5e7ea7dac958..79a8143240d7 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1118,7 +1118,7 @@ static void bpf_object__sanitize_btf_ext(struct bpf_object *obj)
>         }
>  }
>
> -static int bpf_object__load_btf(struct bpf_object *obj,
> +static int bpf_object__init_btf(struct bpf_object *obj,
>                                 Elf_Data *btf_data,
>                                 Elf_Data *btf_ext_data)
>  {
> @@ -1137,13 +1137,6 @@ static int bpf_object__load_btf(struct bpf_object *obj,
>                                    BTF_ELF_SEC, err);
>                         goto out;
>                 }
> -               bpf_object__sanitize_btf(obj);
> -               err = btf__load(obj->btf);
> -               if (err) {
> -                       pr_warning("Error loading %s into kernel: %d.\n",
> -                                  BTF_ELF_SEC, err);
> -                       goto out;
> -               }
>         }
>         if (btf_ext_data) {
>                 if (!obj->btf) {
> @@ -1159,7 +1152,6 @@ static int bpf_object__load_btf(struct bpf_object *obj,
>                         obj->btf_ext = NULL;
>                         goto out;
>                 }
> -               bpf_object__sanitize_btf_ext(obj);
>         }
>  out:
>         if (err || IS_ERR(obj->btf)) {
> @@ -1170,6 +1162,26 @@ static int bpf_object__load_btf(struct bpf_object *obj,
>         return 0;
>  }
>
> +static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
> +{
> +       int err = 0;
> +
> +       if (!obj->btf)
> +               return 0;
> +
> +       bpf_object__sanitize_btf(obj);
> +       bpf_object__sanitize_btf_ext(obj);
> +
> +       err = btf__load(obj->btf);
> +       if (err) {
> +               pr_warning("Error loading %s into kernel: %d.\n",
> +                          BTF_ELF_SEC, err);
> +               btf__free(obj->btf);
> +               obj->btf = NULL;
> +       }
> +       return 0;
> +}
> +
>  static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
>  {
>         Elf *elf = obj->efile.elf;
> @@ -1301,9 +1313,11 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
>                 pr_warning("Corrupted ELF file: index of strtab invalid\n");
>                 return -LIBBPF_ERRNO__FORMAT;
>         }
> -       err = bpf_object__load_btf(obj, btf_data, btf_ext_data);
> +       err = bpf_object__init_btf(obj, btf_data, btf_ext_data);
>         if (!err)
>                 err = bpf_object__init_maps(obj, flags);
> +       if (!err)
> +               err = bpf_object__sanitize_and_load_btf(obj);
>         if (!err)
>                 err = bpf_object__init_prog_names(obj);
>         return err;
> --
> 2.17.1
>