From 1373ff59955621b7e71e7a1152036c93a5780c11 Mon Sep 17 00:00:00 2001 From: Shuyi Cheng Date: Tue, 13 Jul 2021 20:42:37 +0800 Subject: [PATCH] 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 _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: Shuyi Cheng Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/1626180159-112996-2-git-send-email-chengshuyi@linux.alibaba.com --- tools/lib/bpf/libbpf.c | 28 ++++++++++++++++++++++++---- tools/lib/bpf/libbpf.h | 9 ++++++++- 2 files changed, 32 insertions(+), 5 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 4ccfae3..8bff28f 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -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; diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index 6e61342..6b08c10 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -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 * -- 2.7.4