In order to enable the older kernel to use the CO-RE feature, load the vmlinux btf of the specified path. Learn from Andrii's comments in [0], add the btf_custom_path parameter to bpf_obj_open_opts, you can directly use the skeleton's <objname>_bpf__open_opts function to pass in the btf_custom_path parameter. Prior to this, there was also a developer who provided a patch with similar functions. It is a pity that the follow-up did not continue to advance. See [1]. [0]https://lore.kernel.org/bpf/CAEf4BzbJZLjNoiK8_VfeVg_Vrg=9iYFv+po-38SMe=UzwDKJ=Q@xxxxxxxxxxxxxx/#t [1]https://yhbt.net/lore/all/CAEf4Bzbgw49w2PtowsrzKQNcxD4fZRE6AKByX-5-dMo-+oWHHA@xxxxxxxxxxxxxx/ Cc: Andrii Nakryiko <andrii@xxxxxxxxxx> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Signed-off-by: Shuyi Cheng <chengshuyi@xxxxxxxxxxxxxxxxx> --- v1: https://lore.kernel.org/bpf/CAEf4BzaGjEC4t1OefDo11pj2-HfNy0BLhs_G2UREjRNTmb2u=A@xxxxxxxxxxxxxx/t/#m4d9f7c6761fbd2b436b5dfe491cd864b70225804 v1->v2: -- Change custom_btf_path to btf_custom_path. -- If the length of btf_custom_path of bpf_obj_open_opts is too long, return ERR_PTR(-ENAMETOOLONG). -- Add `custom BTF is in addition to vmlinux BTF` with btf_custom_path field. tools/lib/bpf/libbpf.c | 27 ++++++++++++++++++++++++--- tools/lib/bpf/libbpf.h | 6 +++++- 2 files changed, 29 insertions(+), 4 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 1e04ce7..aed156c 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -494,6 +494,10 @@ struct bpf_object { struct btf *btf; struct btf_ext *btf_ext; + /* custom BTF is in addition to vmlinux BTF (i.e., Use the CO-RE + * feature in the old kernel). + */ + char *btf_custom_path; /* Parse and load BTF vmlinux if any of the programs in the object need * it at load time. */ @@ -2679,8 +2683,15 @@ static int bpf_object__load_vmlinux_btf(struct bpf_object *obj, bool force) if (!force && !obj_needs_vmlinux_btf(obj)) return 0; - obj->btf_vmlinux = libbpf_find_kernel_btf(); - err = libbpf_get_error(obj->btf_vmlinux); + if (obj->btf_custom_path) { + obj->btf_vmlinux = btf__parse(obj->btf_custom_path, NULL); + err = libbpf_get_error(obj->btf_vmlinux); + pr_debug("loading custom vmlinux BTF '%s': %d\n", obj->btf_custom_path, err); + } else { + obj->btf_vmlinux = libbpf_find_kernel_btf(); + err = libbpf_get_error(obj->btf_vmlinux); + } + if (err) { pr_warn("Error loading vmlinux BTF: %d\n", err); obj->btf_vmlinux = NULL; @@ -7554,7 +7565,7 @@ int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver) __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]; @@ -7584,6 +7595,15 @@ int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver) obj = bpf_object__new(path, obj_buf, obj_buf_sz, obj_name); 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) + return ERR_PTR(-ENAMETOOLONG); + obj->btf_custom_path = strdup(btf_tmp_path); + if (!obj->btf_custom_path) + return ERR_PTR(-ENOMEM); + } kconfig = OPTS_GET(opts, kconfig, NULL); if (kconfig) { @@ -8702,6 +8722,7 @@ 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; diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index 6e61342..5002d1f 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -94,8 +94,12 @@ struct bpf_object_open_opts { * system Kconfig for CONFIG_xxx externs. */ const char *kconfig; + /* custom BTF is in addition to vmlinux BTF (i.e., Use the CO-RE + * feature in the old kernel). + */ + 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 * -- 1.8.3.1
