[PATCH v3 bpf-next 6/7] libbpf: support kernel module ksym externs
From: Andrii Nakryiko <andrii@kernel.org>
Date: 2021-01-12 07:56:43
Also in:
netdev
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [library] (libbpf), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
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. Acked-by: Yonghong Song <redacted> Acked-by: Hao Luo <redacted> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> --- tools/lib/bpf/libbpf.c | 50 +++++++++++++++++++++++++++--------------- 1 file changed, 32 insertions(+), 18 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6ae748f6ea11..2abbc3800568 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;
@@ -7331,10 +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); }
--
2.24.1