Commit 1373ff59 authored by Shuyi Cheng's avatar Shuyi Cheng Committed by Andrii Nakryiko
Browse files

libbpf: Introduce 'btf_custom_path' to 'bpf_obj_open_opts' 

btf_custom_path allows developers to load custom BTF which libbpf will
subsequently use for CO-RE relocation instead of vmlinux BTF.

Having btf_custom_path in bpf_object_open_opts one can directly use the
skeleton's <objname>_bpf__open_opts() API to pass in the btf_custom_path
parameter, as opposed to using bpf_object__load_xattr() which is slated to be
deprecated ([0]).

This work continues previous work started by another developer ([1]).

  [0] https://lore.kernel.org/bpf/CAEf4BzbJZLjNoiK8_VfeVg_Vrg=9iYFv+po-38SMe=UzwDKJ=Q@mail.gmail.com/#t
  [1] https://yhbt.net/lore/all/CAEf4Bzbgw49w2PtowsrzKQNcxD4fZRE6AKByX-5-dMo-+oWHHA@mail.gmail.com/



Signed-off-by: default avatarShuyi Cheng <chengshuyi@linux.alibaba.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1626180159-112996-2-git-send-email-chengshuyi@linux.alibaba.com
parent 88865347

tools/lib/bpf/libbpf.c

+24 −4
Original line number Diff line number Diff line
@@ -498,6 +498,10 @@ struct bpf_object { 
	 * it at load time.

	 */

	struct btf *btf_vmlinux;

	/* Path to the custom BTF to be used for BPF CO-RE relocations as an

	 * override for vmlinux BTF.

	 */

	char *btf_custom_path;

	/* vmlinux BTF override for CO-RE relocations */

	struct btf *btf_vmlinux_override;

	/* Lazily initialized kernel module BTFs */
@@ -2645,8 +2649,10 @@ static bool obj_needs_vmlinux_btf(const struct bpf_object *obj) 
	struct bpf_program *prog;

	int i;



	/* CO-RE relocations need kernel BTF */

	if (obj->btf_ext && obj->btf_ext->core_relo_info.len)

	/* CO-RE relocations need kernel BTF, only when btf_custom_path

	 * is not specified

	 */

	if (obj->btf_ext && obj->btf_ext->core_relo_info.len && !obj->btf_custom_path)

		return true;



	/* Support for typed ksyms needs kernel BTF */
@@ -7596,7 +7602,7 @@ static struct bpf_object * 
__bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,

		   const struct bpf_object_open_opts *opts)

{

	const char *obj_name, *kconfig;

	const char *obj_name, *kconfig, *btf_tmp_path;

	struct bpf_program *prog;

	struct bpf_object *obj;

	char tmp_name[64];
@@ -7627,6 +7633,19 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz, 
	if (IS_ERR(obj))

		return obj;



	btf_tmp_path = OPTS_GET(opts, btf_custom_path, NULL);

	if (btf_tmp_path) {

		if (strlen(btf_tmp_path) >= PATH_MAX) {

			err = -ENAMETOOLONG;

			goto out;

		}

		obj->btf_custom_path = strdup(btf_tmp_path);

		if (!obj->btf_custom_path) {

			err = -ENOMEM;

			goto out;

		}

	}



	kconfig = OPTS_GET(opts, kconfig, NULL);

	if (kconfig) {

		obj->kconfig = strdup(kconfig);
@@ -8097,7 +8116,7 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr) 
	err = err ? : bpf_object__sanitize_maps(obj);

	err = err ? : bpf_object__init_kern_struct_ops_maps(obj);

	err = err ? : bpf_object__create_maps(obj);

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

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

	err = err ? : bpf_object__load_progs(obj, attr->log_level);



	if (obj->gen_loader) {
@@ -8744,6 +8763,7 @@ void bpf_object__close(struct bpf_object *obj) 
	for (i = 0; i < obj->nr_maps; i++)

		bpf_map__destroy(&obj->maps[i]);



	zfree(&obj->btf_custom_path);

	zfree(&obj->kconfig);

	zfree(&obj->externs);

	obj->nr_extern = 0;

tools/lib/bpf/libbpf.h

+8 −1
Original line number Diff line number Diff line
@@ -94,8 +94,15 @@ struct bpf_object_open_opts { 
	 * system Kconfig for CONFIG_xxx externs.

	 */

	const char *kconfig;

	/* Path to the custom BTF to be used for BPF CO-RE relocations.

	 * This custom BTF completely replaces the use of vmlinux BTF

	 * for the purpose of CO-RE relocations.

	 * NOTE: any other BPF feature (e.g., fentry/fexit programs,

	 * struct_ops, etc) will need actual kernel BTF at /sys/kernel/btf/vmlinux.

	 */

	const char *btf_custom_path;

};

#define bpf_object_open_opts__last_field kconfig

#define bpf_object_open_opts__last_field btf_custom_path



LIBBPF_API struct bpf_object *bpf_object__open(const char *path);

LIBBPF_API struct bpf_object *