Commit 284d2587 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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libbpf: Support kernel module ksym externs 



Add support for searching for ksym externs not just in vmlinux BTF, but across
all module BTFs, similarly to how it's done for CO-RE relocations. 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: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarHao Luo <haoluo@google.com>
Link: https://lore.kernel.org/bpf/20210112075520.4103414-7-andrii@kernel.org
parent 541c3bad

tools/lib/bpf/libbpf.c

+32 −18
Original line number Diff line number Diff line
@@ -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;
@@ -7331,10 +7334,25 @@ 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;

				/* we assume module BTF FD is always >0 */

				btf_fd = obj->btf_modules[j].fd;

				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",

			pr_warn("extern (ksym) '%s': failed to find BTF ID in kernel BTF(s).\n",

				ext->name);

			return -ESRCH;

		}
@@ -7343,24 +7361,19 @@ 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 +7383,8 @@ 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);

	}