On Mon, Jun 10, 2019 at 9:49 PM Andrii Nakryiko <andriin@xxxxxx> 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@xxxxxx>
Acked-by: Song Liu <songliubraving@xxxxxx>
> ---
> 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
>
