Commit ef9356d3 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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bpftool: Improve skeleton generation for data maps without DATASEC type 



It can happen that some data sections (e.g., .rodata.cst16, containing
compiler populated string constants) won't have a corresponding BTF
DATASEC type. Now that libbpf supports .rodata.* and .data.* sections,
situation like that will cause invalid BPF skeleton to be generated that
won't compile successfully, as some parts of skeleton would assume
memory-mapped struct definitions for each special data section.

Fix this by generating empty struct definitions for such data sections.

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211021014404.2635234-7-andrii@kernel.org
parent 8654b4d3

tools/bpf/bpftool/gen.c

+45 −6
Original line number Diff line number Diff line
@@ -213,22 +213,61 @@ static int codegen_datasecs(struct bpf_object *obj, const char *obj_name) 
	struct btf *btf = bpf_object__btf(obj);

	int n = btf__get_nr_types(btf);

	struct btf_dump *d;

	struct bpf_map *map;

	const struct btf_type *sec;

	char sec_ident[256], map_ident[256];

	int i, err = 0;



	d = btf_dump__new(btf, NULL, NULL, codegen_btf_dump_printf);

	if (IS_ERR(d))

		return PTR_ERR(d);



	bpf_object__for_each_map(map, obj) {

		/* only generate definitions for memory-mapped internal maps */

		if (!bpf_map__is_internal(map))

			continue;

		if (!(bpf_map__def(map)->map_flags & BPF_F_MMAPABLE))

			continue;



		if (!get_map_ident(map, map_ident, sizeof(map_ident)))

			continue;



		sec = NULL;

		for (i = 1; i <= n; i++) {

			const struct btf_type *t = btf__type_by_id(btf, i);

			const char *name;



			if (!btf_is_datasec(t))

				continue;



		err = codegen_datasec_def(obj, btf, d, t, obj_name);

			name = btf__str_by_offset(btf, t->name_off);

			if (!get_datasec_ident(name, sec_ident, sizeof(sec_ident)))

				continue;



			if (strcmp(sec_ident, map_ident) == 0) {

				sec = t;

				break;

			}

		}



		/* In some cases (e.g., sections like .rodata.cst16 containing

		 * compiler allocated string constants only) there will be

		 * special internal maps with no corresponding DATASEC BTF

		 * type. In such case, generate empty structs for each such

		 * map. It will still be memory-mapped and its contents

		 * accessible from user-space through BPF skeleton.

		 */

		if (!sec) {

			printf("	struct %s__%s {\n", obj_name, map_ident);

			printf("	} *%s;\n", map_ident);

		} else {

			err = codegen_datasec_def(obj, btf, d, sec, obj_name);

			if (err)

				goto out;

		}

	}





out:

	btf_dump__free(d);

	return err;