tools/bpftool: Add bpftool support for split BTF

Add ability to work with split BTF by providing extra -B flag, which allows to
specify the path to the base BTF file.

Signed-off-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Acked-by: Song Liu <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/bpf/bpftool/btf.c

···
 		}
 	} else {
 		int cnt = btf__get_nr_types(btf);
+		int start_id = 1;
 
-		for (i = 1; i <= cnt; i++) {
+		if (base_btf)
+			start_id = btf__get_nr_types(base_btf) + 1;
+
+		for (i = start_id; i <= cnt; i++) {
 			t = btf__type_by_id(btf, i);
 			dump_btf_type(btf, i, t);
 		}
···
 		return -1;
 	}
 	src = GET_ARG();
-
 	if (is_prefix(src, "map")) {
 		struct bpf_map_info info = {};
 		__u32 len = sizeof(info);
···
 		}
 		NEXT_ARG();
 	} else if (is_prefix(src, "file")) {
-		btf = btf__parse(*argv, NULL);
+		btf = btf__parse_split(*argv, base_btf);
 		if (IS_ERR(btf)) {
 			err = -PTR_ERR(btf);
 			btf = NULL;

tools/bpf/bpftool/main.c

···
 
 #include <bpf/bpf.h>
 #include <bpf/libbpf.h>
+#include <bpf/btf.h>
 
 #include "main.h"
 
···
 bool block_mount;
 bool verifier_logs;
 bool relaxed_maps;
+struct btf *base_btf;
 struct pinned_obj_table prog_table;
 struct pinned_obj_table map_table;
 struct pinned_obj_table link_table;
···
 		{ "mapcompat",	no_argument,	NULL,	'm' },
 		{ "nomount",	no_argument,	NULL,	'n' },
 		{ "debug",	no_argument,	NULL,	'd' },
+		{ "base-btf",	required_argument, NULL, 'B' },
 		{ 0 }
 	};
 	int opt, ret;
···
 	hash_init(link_table.table);
 
 	opterr = 0;
-	while ((opt = getopt_long(argc, argv, "Vhpjfmnd",
+	while ((opt = getopt_long(argc, argv, "VhpjfmndB:",
 				  options, NULL)) >= 0) {
 		switch (opt) {
 		case 'V':
···
 			libbpf_set_print(print_all_levels);
 			verifier_logs = true;
 			break;
+		case 'B':
+			base_btf = btf__parse(optarg, NULL);
+			if (libbpf_get_error(base_btf)) {
+				p_err("failed to parse base BTF at '%s': %ld\n",
+				      optarg, libbpf_get_error(base_btf));
+				base_btf = NULL;
+				return -1;
+			}
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)
···
 		delete_pinned_obj_table(&map_table);
 		delete_pinned_obj_table(&link_table);
 	}
+	btf__free(base_btf);
 
 	return ret;
 }

tools/bpf/bpftool/main.h

···
 extern bool block_mount;
 extern bool verifier_logs;
 extern bool relaxed_maps;
+extern struct btf *base_btf;
 extern struct pinned_obj_table prog_table;
 extern struct pinned_obj_table map_table;
 extern struct pinned_obj_table link_table;