libbpf: Add btf__parse_raw() and generic btf__parse() APIs

Add public APIs to parse BTF from raw data file (e.g.,
/sys/kernel/btf/vmlinux), as well as generic btf__parse(), which will try to
determine correct format, currently either raw or ELF.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200802013219.864880-2-andriin@fb.com

tools/lib/bpf/btf.c

@@ -562,6 +562,83 @@ done:
 	return btf;
 }
 
+struct btf *btf__parse_raw(const char *path)
+{
+	void *data = NULL;
+	struct btf *btf;
+	FILE *f = NULL;
+	__u16 magic;
+	int err = 0;
+	long sz;
+
+	f = fopen(path, "rb");
+	if (!f) {
+		err = -errno;
+		goto err_out;
+	}
+
+	/* check BTF magic */
+	if (fread(&magic, 1, sizeof(magic), f) < sizeof(magic)) {
+		err = -EIO;
+		goto err_out;
+	}
+	if (magic != BTF_MAGIC) {
+		/* definitely not a raw BTF */
+		err = -EPROTO;
+		goto err_out;
+	}
+
+	/* get file size */
+	if (fseek(f, 0, SEEK_END)) {
+		err = -errno;
+		goto err_out;
+	}
+	sz = ftell(f);
+	if (sz < 0) {
+		err = -errno;
+		goto err_out;
+	}
+	/* rewind to the start */
+	if (fseek(f, 0, SEEK_SET)) {
+		err = -errno;
+		goto err_out;
+	}
+
+	/* pre-alloc memory and read all of BTF data */
+	data = malloc(sz);
+	if (!data) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+	if (fread(data, 1, sz, f) < sz) {
+		err = -EIO;
+		goto err_out;
+	}
+
+	/* finally parse BTF data */
+	btf = btf__new(data, sz);
+
+err_out:
+	free(data);
+	if (f)
+		fclose(f);
+	return err ? ERR_PTR(err) : btf;
+}
+
+struct btf *btf__parse(const char *path, struct btf_ext **btf_ext)
+{
+	struct btf *btf;
+
+	if (btf_ext)
+		*btf_ext = NULL;
+
+	btf = btf__parse_raw(path);
+	if (!IS_ERR(btf) || PTR_ERR(btf) != -EPROTO)
+		return btf;
+
+	return btf__parse_elf(path, btf_ext);
+}
+
 static int compare_vsi_off(const void *_a, const void *_b)
 {
 	const struct btf_var_secinfo *a = _a;
@@ -2951,41 +3028,6 @@ static int btf_dedup_remap_types(struct btf_dedup *d)
 	return 0;
 }
 
-static struct btf *btf_load_raw(const char *path)
-{
-	struct btf *btf;
-	size_t read_cnt;
-	struct stat st;
-	void *data;
-	FILE *f;
-
-	if (stat(path, &st))
-		return ERR_PTR(-errno);
-
-	data = malloc(st.st_size);
-	if (!data)
-		return ERR_PTR(-ENOMEM);
-
-	f = fopen(path, "rb");
-	if (!f) {
-		btf = ERR_PTR(-errno);
-		goto cleanup;
-	}
-
-	read_cnt = fread(data, 1, st.st_size, f);
-	fclose(f);
-	if (read_cnt < st.st_size) {
-		btf = ERR_PTR(-EBADF);
-		goto cleanup;
-	}
-
-	btf = btf__new(data, read_cnt);
-
-cleanup:
-	free(data);
-	return btf;
-}
-
 /*
  * Probe few well-known locations for vmlinux kernel image and try to load BTF
  * data out of it to use for target BTF.
@@ -3021,7 +3063,7 @@ struct btf *libbpf_find_kernel_btf(void)
 			continue;
 
 		if (locations[i].raw_btf)
-			btf = btf_load_raw(path);
+			btf = btf__parse_raw(path);
 		else
 			btf = btf__parse_elf(path, NULL);
 

tools/lib/bpf/btf.h

@@ -64,8 +64,9 @@ struct btf_ext_header {
 
 LIBBPF_API void btf__free(struct btf *btf);
 LIBBPF_API struct btf *btf__new(const void *data, __u32 size);
-LIBBPF_API struct btf *btf__parse_elf(const char *path,
+LIBBPF_API struct btf *btf__parse(const char *path, struct btf_ext **btf_ext);
-				      struct btf_ext **btf_ext);
+LIBBPF_API struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext);
+LIBBPF_API struct btf *btf__parse_raw(const char *path);
 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,

tools/lib/bpf/libbpf.map

@@ -293,5 +293,7 @@ LIBBPF_0.1.0 {
 		bpf_program__is_sk_lookup;
 		bpf_program__set_autoload;
 		bpf_program__set_sk_lookup;
+		btf__parse;
+		btf__parse_raw;
 		btf__set_fd;
 } LIBBPF_0.0.9;