bpf, libbpf: add support for BTF Var and DataSec

This adds libbpf support for BTF Var and DataSec kinds. Main point
here is that libbpf needs to do some preparatory work before the
whole BTF object can be loaded into the kernel, that is, fixing up
of DataSec size taken from the ELF section size and non-static
variable offset which needs to be taken from the ELF's string section.

Upstream LLVM doesn't fix these up since at time of BTF emission
it is too early in the compilation process thus this information
isn't available yet, hence loader needs to take care of it.

Note, deduplication handling has not been in the scope of this work
and needs to be addressed in a future commit.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://reviews.llvm.org/D59441
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 28a1e1e59861..c7b399e81fce 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -21,6 +21,8 @@ struct btf;
 struct btf_ext;
 struct btf_type;
 
+struct bpf_object;
+
 /*
  * The .BTF.ext ELF section layout defined as
  *   struct btf_ext_header
@@ -57,6 +59,7 @@ struct btf_ext_header {
 
 LIBBPF_API void btf__free(struct btf *btf);
 LIBBPF_API struct btf *btf__new(__u8 *data, __u32 size);
+LIBBPF_API int btf__finalize_data(struct bpf_object *obj, struct btf *btf);
 LIBBPF_API int btf__load(struct btf *btf);
 LIBBPF_API __s32 btf__find_by_name(const struct btf *btf,
 				   const char *type_name);