Commit 809a69d6 authored by Kui-Feng Lee's avatar Kui-Feng Lee Committed by Martin KaFai Lau
Browse files

libbpf: Use .struct_ops.link section to indicate a struct_ops with a link. 



Flags a struct_ops is to back a bpf_link by putting it to the
".struct_ops.link" section.  Once it is flagged, the created
struct_ops can be used to create a bpf_link or update a bpf_link that
has been backed by another struct_ops.

Signed-off-by: default avatarKui-Feng Lee <kuifeng@meta.com>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230323032405.3735486-8-kuifeng@meta.com


Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
parent 912dd4b0

tools/lib/bpf/libbpf.c

+44 −16
Original line number Diff line number Diff line
@@ -468,6 +468,7 @@ struct bpf_struct_ops { 
#define KCONFIG_SEC ".kconfig"

#define KSYMS_SEC ".ksyms"

#define STRUCT_OPS_SEC ".struct_ops"

#define STRUCT_OPS_LINK_SEC ".struct_ops.link"



enum libbpf_map_type {

	LIBBPF_MAP_UNSPEC,
@@ -597,6 +598,7 @@ struct elf_state { 
	Elf64_Ehdr *ehdr;

	Elf_Data *symbols;

	Elf_Data *st_ops_data;

	Elf_Data *st_ops_link_data;

	size_t shstrndx; /* section index for section name strings */

	size_t strtabidx;

	struct elf_sec_desc *secs;
@@ -606,6 +608,7 @@ struct elf_state { 
	int text_shndx;

	int symbols_shndx;

	int st_ops_shndx;

	int st_ops_link_shndx;

};



struct usdt_manager;
@@ -1119,7 +1122,8 @@ static int bpf_object__init_kern_struct_ops_maps(struct bpf_object *obj) 
	return 0;

}



static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)

static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,

				int shndx, Elf_Data *data, __u32 map_flags)

{

	const struct btf_type *type, *datasec;

	const struct btf_var_secinfo *vsi;
@@ -1130,15 +1134,15 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj) 
	struct bpf_map *map;

	__u32 i;



	if (obj->efile.st_ops_shndx == -1)

	if (shndx == -1)

		return 0;



	btf = obj->btf;

	datasec_id = btf__find_by_name_kind(btf, STRUCT_OPS_SEC,

	datasec_id = btf__find_by_name_kind(btf, sec_name,

					    BTF_KIND_DATASEC);

	if (datasec_id < 0) {

		pr_warn("struct_ops init: DATASEC %s not found\n",

			STRUCT_OPS_SEC);

			sec_name);

		return -EINVAL;

	}
@@ -1151,7 +1155,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj) 
		type_id = btf__resolve_type(obj->btf, vsi->type);

		if (type_id < 0) {

			pr_warn("struct_ops init: Cannot resolve var type_id %u in DATASEC %s\n",

				vsi->type, STRUCT_OPS_SEC);

				vsi->type, sec_name);

			return -EINVAL;

		}
@@ -1170,7 +1174,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj) 
		if (IS_ERR(map))

			return PTR_ERR(map);



		map->sec_idx = obj->efile.st_ops_shndx;

		map->sec_idx = shndx;

		map->sec_offset = vsi->offset;

		map->name = strdup(var_name);

		if (!map->name)
@@ -1180,6 +1184,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj) 
		map->def.key_size = sizeof(int);

		map->def.value_size = type->size;

		map->def.max_entries = 1;

		map->def.map_flags = map_flags;



		map->st_ops = calloc(1, sizeof(*map->st_ops));

		if (!map->st_ops)
@@ -1192,14 +1197,14 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj) 
		if (!st_ops->data || !st_ops->progs || !st_ops->kern_func_off)

			return -ENOMEM;



		if (vsi->offset + type->size > obj->efile.st_ops_data->d_size) {

		if (vsi->offset + type->size > data->d_size) {

			pr_warn("struct_ops init: var %s is beyond the end of DATASEC %s\n",

				var_name, STRUCT_OPS_SEC);

				var_name, sec_name);

			return -EINVAL;

		}



		memcpy(st_ops->data,

		       obj->efile.st_ops_data->d_buf + vsi->offset,

		       data->d_buf + vsi->offset,

		       type->size);

		st_ops->tname = tname;

		st_ops->type = type;
@@ -1212,6 +1217,19 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj) 
	return 0;

}



static int bpf_object_init_struct_ops(struct bpf_object *obj)

{

	int err;



	err = init_struct_ops_maps(obj, STRUCT_OPS_SEC, obj->efile.st_ops_shndx,

				   obj->efile.st_ops_data, 0);

	err = err ?: init_struct_ops_maps(obj, STRUCT_OPS_LINK_SEC,

					  obj->efile.st_ops_link_shndx,

					  obj->efile.st_ops_link_data,

					  BPF_F_LINK);

	return err;

}



static struct bpf_object *bpf_object__new(const char *path,

					  const void *obj_buf,

					  size_t obj_buf_sz,
@@ -1248,6 +1266,7 @@ static struct bpf_object *bpf_object__new(const char *path, 
	obj->efile.obj_buf_sz = obj_buf_sz;

	obj->efile.btf_maps_shndx = -1;

	obj->efile.st_ops_shndx = -1;

	obj->efile.st_ops_link_shndx = -1;

	obj->kconfig_map_idx = -1;



	obj->kern_version = get_kernel_version();
@@ -1265,6 +1284,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj) 
	obj->efile.elf = NULL;

	obj->efile.symbols = NULL;

	obj->efile.st_ops_data = NULL;

	obj->efile.st_ops_link_data = NULL;



	zfree(&obj->efile.secs);

	obj->efile.sec_cnt = 0;
@@ -2619,7 +2639,7 @@ static int bpf_object__init_maps(struct bpf_object *obj, 
	err = bpf_object__init_user_btf_maps(obj, strict, pin_root_path);

	err = err ?: bpf_object__init_global_data_maps(obj);

	err = err ?: bpf_object__init_kconfig_map(obj);

	err = err ?: bpf_object__init_struct_ops_maps(obj);

	err = err ?: bpf_object_init_struct_ops(obj);



	return err;

}
@@ -2753,12 +2773,13 @@ static bool libbpf_needs_btf(const struct bpf_object *obj) 
{

	return obj->efile.btf_maps_shndx >= 0 ||

	       obj->efile.st_ops_shndx >= 0 ||

	       obj->efile.st_ops_link_shndx >= 0 ||

	       obj->nr_extern > 0;

}



static bool kernel_needs_btf(const struct bpf_object *obj)

{

	return obj->efile.st_ops_shndx >= 0;

	return obj->efile.st_ops_shndx >= 0 || obj->efile.st_ops_link_shndx >= 0;

}



static int bpf_object__init_btf(struct bpf_object *obj,
@@ -3451,6 +3472,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj) 
			} else if (strcmp(name, STRUCT_OPS_SEC) == 0) {

				obj->efile.st_ops_data = data;

				obj->efile.st_ops_shndx = idx;

			} else if (strcmp(name, STRUCT_OPS_LINK_SEC) == 0) {

				obj->efile.st_ops_link_data = data;

				obj->efile.st_ops_link_shndx = idx;

			} else {

				pr_info("elf: skipping unrecognized data section(%d) %s\n",

					idx, name);
@@ -3465,6 +3489,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj) 
			/* Only do relo for section with exec instructions */

			if (!section_have_execinstr(obj, targ_sec_idx) &&

			    strcmp(name, ".rel" STRUCT_OPS_SEC) &&

			    strcmp(name, ".rel" STRUCT_OPS_LINK_SEC) &&

			    strcmp(name, ".rel" MAPS_ELF_SEC)) {

				pr_info("elf: skipping relo section(%d) %s for section(%d) %s\n",

					idx, name, targ_sec_idx,
@@ -6611,7 +6636,7 @@ static int bpf_object__collect_relos(struct bpf_object *obj) 
			return -LIBBPF_ERRNO__INTERNAL;

		}



		if (idx == obj->efile.st_ops_shndx)

		if (idx == obj->efile.st_ops_shndx || idx == obj->efile.st_ops_link_shndx)

			err = bpf_object__collect_st_ops_relos(obj, shdr, data);

		else if (idx == obj->efile.btf_maps_shndx)

			err = bpf_object__collect_map_relos(obj, shdr, data);
@@ -8853,6 +8878,7 @@ const char *libbpf_bpf_prog_type_str(enum bpf_prog_type t) 
}



static struct bpf_map *find_struct_ops_map_by_offset(struct bpf_object *obj,

						     int sec_idx,

						     size_t offset)

{

	struct bpf_map *map;
@@ -8862,7 +8888,8 @@ static struct bpf_map *find_struct_ops_map_by_offset(struct bpf_object *obj, 
		map = &obj->maps[i];

		if (!bpf_map__is_struct_ops(map))

			continue;

		if (map->sec_offset <= offset &&

		if (map->sec_idx == sec_idx &&

		    map->sec_offset <= offset &&

		    offset - map->sec_offset < map->def.value_size)

			return map;

	}
@@ -8904,7 +8931,7 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj, 
		}



		name = elf_sym_str(obj, sym->st_name) ?: "<?>";

		map = find_struct_ops_map_by_offset(obj, rel->r_offset);

		map = find_struct_ops_map_by_offset(obj, shdr->sh_info, rel->r_offset);

		if (!map) {

			pr_warn("struct_ops reloc: cannot find map at rel->r_offset %zu\n",

				(size_t)rel->r_offset);
@@ -8971,8 +8998,9 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj, 
		}



		/* struct_ops BPF prog can be re-used between multiple

		 * .struct_ops as long as it's the same struct_ops struct

		 * definition and the same function pointer field

		 * .struct_ops & .struct_ops.link as long as it's the

		 * same struct_ops struct definition and the same

		 * function pointer field

		 */

		if (prog->attach_btf_id != st_ops->type_id ||

		    prog->expected_attach_type != member_idx) {