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: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Hao Luo <haoluo@google.com>
Link: https://lore.kernel.org/bpf/20210112075520.4103414-7-andrii@kernel.org

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6ae748f..2abbc38 100644 (file)
--- 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 @@ out:
 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);
        }