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Tue, 12 Jan 2021 01:34:32 +0000 Subject: Re: [PATCH v2 bpf-next 6/7] libbpf: support kernel module ksym externs To: Andrii Nakryiko CC: Andrii Nakryiko , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team , Hao Luo References: <20210108220930.482456-1-andrii@kernel.org> <20210108220930.482456-7-andrii@kernel.org> From: Yonghong Song Message-ID: Date: Mon, 11 Jan 2021 17:34:30 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:7b7c] X-ClientProxiedBy: BYAPR02CA0055.namprd02.prod.outlook.com (2603:10b6:a03:54::32) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21e1::190b] (2620:10d:c090:400::5:7b7c) by BYAPR02CA0055.namprd02.prod.outlook.com (2603:10b6:a03:54::32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3742.6 via Frontend Transport; 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Kernels >>> that expose module BTFs through sysfs are assumed to support new ldimm64 >>> instruction extension with BTF FD provided in insn[1].imm field, so no extra >>> feature detection is performed. >>> >>> Signed-off-by: Andrii Nakryiko >>> --- >>> tools/lib/bpf/libbpf.c | 47 +++++++++++++++++++++++++++--------------- >>> 1 file changed, 30 insertions(+), 17 deletions(-) >>> >>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c >>> index 6ae748f6ea11..57559a71e4de 100644 >>> --- a/tools/lib/bpf/libbpf.c >>> +++ b/tools/lib/bpf/libbpf.c >>> @@ -395,7 +395,8 @@ struct extern_desc { >>> unsigned long long addr; >>> >>> /* target btf_id of the corresponding kernel var. */ >>> - int vmlinux_btf_id; >>> + int kernel_btf_obj_fd; >>> + int kernel_btf_id; >>> >>> /* local btf_id of the ksym extern's type. */ >>> __u32 type_id; >>> @@ -6162,7 +6163,8 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog) >>> } else /* EXT_KSYM */ { >>> if (ext->ksym.type_id) { /* typed ksyms */ >>> insn[0].src_reg = BPF_PSEUDO_BTF_ID; >>> - insn[0].imm = ext->ksym.vmlinux_btf_id; >>> + insn[0].imm = ext->ksym.kernel_btf_id; >>> + insn[1].imm = ext->ksym.kernel_btf_obj_fd; >>> } else { /* typeless ksyms */ >>> insn[0].imm = (__u32)ext->ksym.addr; >>> insn[1].imm = ext->ksym.addr >> 32; >>> @@ -7319,7 +7321,8 @@ static int bpf_object__read_kallsyms_file(struct bpf_object *obj) >>> static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj) >>> { >>> struct extern_desc *ext; >>> - int i, id; >>> + struct btf *btf; >>> + int i, j, id, btf_fd, err; >>> >>> for (i = 0; i < obj->nr_extern; i++) { >>> const struct btf_type *targ_var, *targ_type; >>> @@ -7331,8 +7334,22 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj) >>> if (ext->type != EXT_KSYM || !ext->ksym.type_id) >>> continue; >>> >>> - id = btf__find_by_name_kind(obj->btf_vmlinux, ext->name, >>> - BTF_KIND_VAR); >>> + btf = obj->btf_vmlinux; >>> + btf_fd = 0; >>> + id = btf__find_by_name_kind(btf, ext->name, BTF_KIND_VAR); >>> + if (id == -ENOENT) { >>> + err = load_module_btfs(obj); >>> + if (err) >>> + return err; >>> + >>> + for (j = 0; j < obj->btf_module_cnt; j++) { >>> + btf = obj->btf_modules[j].btf; >>> + btf_fd = obj->btf_modules[j].fd; >> >> Do we have possibility btf_fd == 0 here? > > Extremely unlikely. But if we are really worried about 0 fd, we should > handle that in a centralized fashion in libbpf. I.e., for any > operation that can return FD, check if that FD is 0, and if yes, dup() > it. And then make everything call that helper. So in the context of > this patch I'm just ignoring such possibility. Maybe at least add some comments here to document such a possibility? > >> >>> + id = btf__find_by_name_kind(btf, ext->name, BTF_KIND_VAR); >>> + if (id != -ENOENT) >>> + break; >>> + } >>> + } >>> if (id <= 0) { >>> pr_warn("extern (ksym) '%s': failed to find BTF ID in vmlinux BTF.\n", >>> ext->name); >>> @@ -7343,24 +7360,19 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj) >>> local_type_id = ext->ksym.type_id; >>> >>> /* find target type_id */ >>> - targ_var = btf__type_by_id(obj->btf_vmlinux, id); >>> - targ_var_name = btf__name_by_offset(obj->btf_vmlinux, >>> - targ_var->name_off); >>> - targ_type = skip_mods_and_typedefs(obj->btf_vmlinux, >>> - targ_var->type, >>> - &targ_type_id); >>> + targ_var = btf__type_by_id(btf, id); >>> + targ_var_name = btf__name_by_offset(btf, targ_var->name_off); >>> + targ_type = skip_mods_and_typedefs(btf, targ_var->type, &targ_type_id); >>> >>> ret = bpf_core_types_are_compat(obj->btf, local_type_id, >>> - obj->btf_vmlinux, targ_type_id); >>> + btf, targ_type_id); >>> if (ret <= 0) { >>> const struct btf_type *local_type; >>> const char *targ_name, *local_name; >>> >>> local_type = btf__type_by_id(obj->btf, local_type_id); >>> - local_name = btf__name_by_offset(obj->btf, >>> - local_type->name_off); >>> - targ_name = btf__name_by_offset(obj->btf_vmlinux, >>> - targ_type->name_off); >>> + local_name = btf__name_by_offset(obj->btf, local_type->name_off); >>> + targ_name = btf__name_by_offset(btf, targ_type->name_off); >>> >>> pr_warn("extern (ksym) '%s': incompatible types, expected [%d] %s %s, but kernel has [%d] %s %s\n", >>> ext->name, local_type_id, >>> @@ -7370,7 +7382,8 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj) >>> } >>> >>> ext->is_set = true; >>> - ext->ksym.vmlinux_btf_id = id; >>> + ext->ksym.kernel_btf_obj_fd = btf_fd; >>> + ext->ksym.kernel_btf_id = id; >>> pr_debug("extern (ksym) '%s': resolved to [%d] %s %s\n", >>> ext->name, id, btf_kind_str(targ_var), targ_var_name); >>> } >>>