Commit 6fbf129c authored by Donglin Peng's avatar Donglin Peng Committed by Andrii Nakryiko
Browse files

libbpf: Add BTF permutation support for type reordering 



Introduce btf__permute() API to allow in-place rearrangement of BTF types.
This function reorganizes BTF type order according to a provided array of
type IDs, updating all type references to maintain consistency.

Signed-off-by: default avatarDonglin Peng <pengdonglin@xiaomi.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260109130003.3313716-2-dolinux.peng@gmail.com
parent c9c9f6bf

tools/lib/bpf/btf.c

+133 −0
Original line number Diff line number Diff line
@@ -5887,3 +5887,136 @@ int btf__relocate(struct btf *btf, const struct btf *base_btf) 
		btf->owns_base = false;

	return libbpf_err(err);

}



struct btf_permute {

	struct btf *btf;

	__u32 *id_map;

	__u32 start_offs;

};



/* Callback function to remap individual type ID references */

static int btf_permute_remap_type_id(__u32 *type_id, void *ctx)

{

	struct btf_permute *p = ctx;

	__u32 new_id = *type_id;



	/* refer to the base BTF or VOID type */

	if (new_id < p->btf->start_id)

		return 0;



	if (new_id >= btf__type_cnt(p->btf))

		return -EINVAL;



	*type_id = p->id_map[new_id - p->btf->start_id + p->start_offs];

	return 0;

}



int btf__permute(struct btf *btf, __u32 *id_map, __u32 id_map_cnt,

		 const struct btf_permute_opts *opts)

{

	struct btf_permute p;

	struct btf_ext *btf_ext;

	void *nt, *new_types = NULL;

	__u32 *order_map = NULL;

	int err = 0, i;

	__u32 n, id, start_offs = 0;



	if (!OPTS_VALID(opts, btf_permute_opts))

		return libbpf_err(-EINVAL);



	if (btf__base_btf(btf)) {

		n = btf->nr_types;

	} else {

		if (id_map[0] != 0)

			return libbpf_err(-EINVAL);

		n = btf__type_cnt(btf);

		start_offs = 1;

	}



	if (id_map_cnt != n)

		return libbpf_err(-EINVAL);



	/* record the sequence of types */

	order_map = calloc(id_map_cnt, sizeof(*id_map));

	if (!order_map) {

		err = -ENOMEM;

		goto done;

	}



	new_types = calloc(btf->hdr->type_len, 1);

	if (!new_types) {

		err = -ENOMEM;

		goto done;

	}



	if (btf_ensure_modifiable(btf)) {

		err = -ENOMEM;

		goto done;

	}



	for (i = start_offs; i < id_map_cnt; i++) {

		id = id_map[i];

		if (id < btf->start_id || id >= btf__type_cnt(btf)) {

			err = -EINVAL;

			goto done;

		}

		id -= btf->start_id - start_offs;

		/* cannot be mapped to the same ID */

		if (order_map[id]) {

			err = -EINVAL;

			goto done;

		}

		order_map[id] = i + btf->start_id - start_offs;

	}



	p.btf = btf;

	p.id_map = id_map;

	p.start_offs = start_offs;

	nt = new_types;

	for (i = start_offs; i < id_map_cnt; i++) {

		struct btf_field_iter it;

		const struct btf_type *t;

		__u32 *type_id;

		int type_size;



		id = order_map[i];

		t = btf__type_by_id(btf, id);

		type_size = btf_type_size(t);

		memcpy(nt, t, type_size);



		/* fix up referenced IDs for BTF */

		err = btf_field_iter_init(&it, nt, BTF_FIELD_ITER_IDS);

		if (err)

			goto done;

		while ((type_id = btf_field_iter_next(&it))) {

			err = btf_permute_remap_type_id(type_id, &p);

			if (err)

				goto done;

		}



		nt += type_size;

	}



	/* fix up referenced IDs for btf_ext */

	btf_ext = OPTS_GET(opts, btf_ext, NULL);

	if (btf_ext) {

		err = btf_ext_visit_type_ids(btf_ext, btf_permute_remap_type_id, &p);

		if (err)

			goto done;

	}



	for (nt = new_types, i = 0; i < id_map_cnt - start_offs; i++) {

		btf->type_offs[i] = nt - new_types;

		nt += btf_type_size(nt);

	}



	free(order_map);

	free(btf->types_data);

	btf->types_data = new_types;

	return 0;



done:

	free(order_map);

	free(new_types);

	return libbpf_err(err);

}

tools/lib/bpf/btf.h

+42 −0
Original line number Diff line number Diff line
@@ -281,6 +281,48 @@ LIBBPF_API int btf__dedup(struct btf *btf, const struct btf_dedup_opts *opts); 
 */

LIBBPF_API int btf__relocate(struct btf *btf, const struct btf *base_btf);



struct btf_permute_opts {

	size_t sz;

	/* optional .BTF.ext info along the main BTF info */

	struct btf_ext *btf_ext;

	size_t :0;

};

#define btf_permute_opts__last_field btf_ext



/**

 * @brief **btf__permute()** rearranges BTF types in-place according to a specified ID mapping

 * @param btf BTF object to permute

 * @param id_map Array mapping original type IDs to new IDs

 * @param id_map_cnt Number of elements in @id_map

 * @param opts Optional parameters, including BTF extension data for reference updates

 * @return 0 on success, negative error code on failure

 *

 * **btf__permute()** reorders BTF types based on the provided @id_map array,

 * updating all internal type references to maintain consistency. The function

 * operates in-place, modifying the BTF object directly.

 *

 * For **base BTF**:

 * - @id_map must include all types from ID 0 to `btf__type_cnt(btf) - 1`

 * - @id_map_cnt must be `btf__type_cnt(btf)`

 * - Mapping is defined as `id_map[original_id] = new_id`

 * - `id_map[0]` must be 0 (void type cannot be moved)

 *

 * For **split BTF**:

 * - @id_map must include only split types (types added on top of the base BTF)

 * - @id_map_cnt must be `btf__type_cnt(btf) - btf__type_cnt(btf__base_btf(btf))`

 * - Mapping is defined as `id_map[original_id - start_id] = new_id`

 * - `start_id` equals `btf__type_cnt(btf__base_btf(btf))`

 *

 * After permutation, all type references within the BTF data and optional

 * BTF extension (if provided via @opts) are updated automatically.

 *

 * On error, returns a negative error code and sets errno:

 *   - `-EINVAL`: Invalid parameters or invalid ID mapping

 *   - `-ENOMEM`: Memory allocation failure

 */

LIBBPF_API int btf__permute(struct btf *btf, __u32 *id_map, __u32 id_map_cnt,

			    const struct btf_permute_opts *opts);



struct btf_dump;



struct btf_dump_opts {

tools/lib/bpf/libbpf.map

+1 −0
Original line number Diff line number Diff line
@@ -453,4 +453,5 @@ LIBBPF_1.7.0 { 
		bpf_map__exclusive_program;

		bpf_prog_assoc_struct_ops;

		bpf_program__assoc_struct_ops;

		btf__permute;

} LIBBPF_1.6.0;