Commit 1315c28e authored by Mykyta Yatsenko's avatar Mykyta Yatsenko Committed by Alexei Starovoitov
Browse files

libbpf: Split bpf object load into prepare/load 



Introduce bpf_object__prepare API: additional intermediate preparation
step that performs ELF processing, relocations, prepares final state of
BPF program instructions (accessible with bpf_program__insns()), creates
and (potentially) pins maps, and stops short of loading BPF programs.

We anticipate few use cases for this API, such as:
* Use prepare to initialize bpf_token, without loading freplace
programs, unlocking possibility to lookup BTF of other programs.
* Execute prepare to obtain finalized BPF program instructions without
loading programs, enabling tools like veristat to process one program at
a time, without incurring cost of ELF parsing and processing.

Signed-off-by: default avatarMykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250303135752.158343-4-mykyta.yatsenko5@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 9a9e3478

tools/lib/bpf/libbpf.c

+103 −43
Original line number Diff line number Diff line
@@ -7901,13 +7901,6 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level) 
	size_t i;

	int err;



	for (i = 0; i < obj->nr_programs; i++) {

		prog = &obj->programs[i];

		err = bpf_object__sanitize_prog(obj, prog);

		if (err)

			return err;

	}



	for (i = 0; i < obj->nr_programs; i++) {

		prog = &obj->programs[i];

		if (prog_is_subprog(obj, prog))
@@ -7933,6 +7926,21 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level) 
	return 0;

}



static int bpf_object_prepare_progs(struct bpf_object *obj)

{

	struct bpf_program *prog;

	size_t i;

	int err;



	for (i = 0; i < obj->nr_programs; i++) {

		prog = &obj->programs[i];

		err = bpf_object__sanitize_prog(obj, prog);

		if (err)

			return err;

	}

	return 0;

}



static const struct bpf_sec_def *find_sec_def(const char *sec_name);



static int bpf_object_init_progs(struct bpf_object *obj, const struct bpf_object_open_opts *opts)
@@ -8549,9 +8557,72 @@ static int bpf_object_prepare_struct_ops(struct bpf_object *obj) 
	return 0;

}



static void bpf_object_unpin(struct bpf_object *obj)

{

	int i;



	/* unpin any maps that were auto-pinned during load */

	for (i = 0; i < obj->nr_maps; i++)

		if (obj->maps[i].pinned && !obj->maps[i].reused)

			bpf_map__unpin(&obj->maps[i], NULL);

}



static void bpf_object_post_load_cleanup(struct bpf_object *obj)

{

	int i;



	/* clean up fd_array */

	zfree(&obj->fd_array);



	/* clean up module BTFs */

	for (i = 0; i < obj->btf_module_cnt; i++) {

		close(obj->btf_modules[i].fd);

		btf__free(obj->btf_modules[i].btf);

		free(obj->btf_modules[i].name);

	}

	obj->btf_module_cnt = 0;

	zfree(&obj->btf_modules);



	/* clean up vmlinux BTF */

	btf__free(obj->btf_vmlinux);

	obj->btf_vmlinux = NULL;

}



static int bpf_object_prepare(struct bpf_object *obj, const char *target_btf_path)

{

	int err;



	if (obj->state >= OBJ_PREPARED) {

		pr_warn("object '%s': prepare loading can't be attempted twice\n", obj->name);

		return -EINVAL;

	}



	err = bpf_object_prepare_token(obj);

	err = err ? : bpf_object__probe_loading(obj);

	err = err ? : bpf_object__load_vmlinux_btf(obj, false);

	err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);

	err = err ? : bpf_object__sanitize_maps(obj);

	err = err ? : bpf_object__init_kern_struct_ops_maps(obj);

	err = err ? : bpf_object_adjust_struct_ops_autoload(obj);

	err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);

	err = err ? : bpf_object__sanitize_and_load_btf(obj);

	err = err ? : bpf_object__create_maps(obj);

	err = err ? : bpf_object_prepare_progs(obj);



	if (err) {

		bpf_object_unpin(obj);

		bpf_object_unload(obj);

		obj->state = OBJ_LOADED;

		return err;

	}



	obj->state = OBJ_PREPARED;

	return 0;

}



static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)

{

	int err, i;

	int err;



	if (!obj)

		return libbpf_err(-EINVAL);
@@ -8571,17 +8642,12 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch 
		return libbpf_err(-LIBBPF_ERRNO__ENDIAN);

	}



	err = bpf_object_prepare_token(obj);

	err = err ? : bpf_object__probe_loading(obj);

	err = err ? : bpf_object__load_vmlinux_btf(obj, false);

	err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);

	err = err ? : bpf_object__sanitize_maps(obj);

	err = err ? : bpf_object__init_kern_struct_ops_maps(obj);

	err = err ? : bpf_object_adjust_struct_ops_autoload(obj);

	err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);

	err = err ? : bpf_object__sanitize_and_load_btf(obj);

	err = err ? : bpf_object__create_maps(obj);

	err = err ? : bpf_object__load_progs(obj, extra_log_level);

	if (obj->state < OBJ_PREPARED) {

		err = bpf_object_prepare(obj, target_btf_path);

		if (err)

			return libbpf_err(err);

	}

	err = bpf_object__load_progs(obj, extra_log_level);

	err = err ? : bpf_object_init_prog_arrays(obj);

	err = err ? : bpf_object_prepare_struct_ops(obj);
@@ -8593,37 +8659,24 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch 
			err = bpf_gen__finish(obj->gen_loader, obj->nr_programs, obj->nr_maps);

	}



	/* clean up fd_array */

	zfree(&obj->fd_array);



	/* clean up module BTFs */

	for (i = 0; i < obj->btf_module_cnt; i++) {

		close(obj->btf_modules[i].fd);

		btf__free(obj->btf_modules[i].btf);

		free(obj->btf_modules[i].name);

	}

	free(obj->btf_modules);



	/* clean up vmlinux BTF */

	btf__free(obj->btf_vmlinux);

	obj->btf_vmlinux = NULL;



	bpf_object_post_load_cleanup(obj);

	obj->state = OBJ_LOADED; /* doesn't matter if successfully or not */

	if (err)

		goto out;



	return 0;

out:

	/* unpin any maps that were auto-pinned during load */

	for (i = 0; i < obj->nr_maps; i++)

		if (obj->maps[i].pinned && !obj->maps[i].reused)

			bpf_map__unpin(&obj->maps[i], NULL);



	if (err) {

		bpf_object_unpin(obj);

		bpf_object_unload(obj);

		pr_warn("failed to load object '%s'\n", obj->path);

		return libbpf_err(err);

	}



	return 0;

}



int bpf_object__prepare(struct bpf_object *obj)

{

	return libbpf_err(bpf_object_prepare(obj, NULL));

}



int bpf_object__load(struct bpf_object *obj)

{

	return bpf_object_load(obj, 0, NULL);
@@ -9069,6 +9122,13 @@ void bpf_object__close(struct bpf_object *obj) 
	if (IS_ERR_OR_NULL(obj))

		return;



	/*

	 * if user called bpf_object__prepare() without ever getting to

	 * bpf_object__load(), we need to clean up stuff that is normally

	 * cleaned up at the end of loading step

	 */

	bpf_object_post_load_cleanup(obj);



	usdt_manager_free(obj->usdt_man);

	obj->usdt_man = NULL;

tools/lib/bpf/libbpf.h

+13 −0
Original line number Diff line number Diff line
@@ -241,6 +241,19 @@ LIBBPF_API struct bpf_object * 
bpf_object__open_mem(const void *obj_buf, size_t obj_buf_sz,

		     const struct bpf_object_open_opts *opts);



/**

 * @brief **bpf_object__prepare()** prepares BPF object for loading:

 * performs ELF processing, relocations, prepares final state of BPF program

 * instructions (accessible with bpf_program__insns()), creates and

 * (potentially) pins maps. Leaves BPF object in the state ready for program

 * loading.

 * @param obj Pointer to a valid BPF object instance returned by

 * **bpf_object__open*()** API

 * @return 0, on success; negative error code, otherwise, error code is

 * stored in errno

 */

int bpf_object__prepare(struct bpf_object *obj);



/**

 * @brief **bpf_object__load()** loads BPF object into kernel.

 * @param obj Pointer to a valid BPF object instance returned by

tools/lib/bpf/libbpf.map

+1 −0
Original line number Diff line number Diff line
@@ -436,6 +436,7 @@ LIBBPF_1.6.0 { 
		bpf_linker__add_buf;

		bpf_linker__add_fd;

		bpf_linker__new_fd;

		bpf_object__prepare;

		btf__add_decl_attr;

		btf__add_type_attr;

} LIBBPF_1.5.0;