btf: expose API to work with raw btf data

This patch exposes new API btf__get_raw_data() that allows to get a copy
of raw BTF data out of struct btf. This is useful for external programs
that need to manipulate raw data, e.g., pahole using btf__dedup() to
deduplicate BTF type info and then writing it back to file.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/btf.c

@@ -439,6 +439,12 @@ int btf__fd(const struct btf *btf)
 	return btf->fd;
 }
 
+const void *btf__get_raw_data(const struct btf *btf, __u32 *size)
+{
+	*size = btf->data_size;
+	return btf->data;
+}
+
 void btf__get_strings(const struct btf *btf, const char **strings,
 		      __u32 *str_len)
 {

tools/lib/bpf/btf.h

@@ -66,6 +66,7 @@ LIBBPF_API const struct btf_type *btf__type_by_id(const struct btf *btf,
 LIBBPF_API __s64 btf__resolve_size(const struct btf *btf, __u32 type_id);
 LIBBPF_API int btf__resolve_type(const struct btf *btf, __u32 type_id);
 LIBBPF_API int btf__fd(const struct btf *btf);
+LIBBPF_API const void *btf__get_raw_data(const struct btf *btf, __u32 *size);
 LIBBPF_API void btf__get_strings(const struct btf *btf, const char **strings,
 				 __u32 *str_len);
 LIBBPF_API const char *btf__name_by_offset(const struct btf *btf, __u32 offset);

tools/lib/bpf/libbpf.map

@@ -136,6 +136,7 @@ LIBBPF_0.0.2 {
 		btf__dedup;
 		btf__get_map_kv_tids;
 		btf__get_nr_types;
+		btf__get_raw_data;
 		btf__get_strings;
 		btf__load;
 		btf_ext__free;