libbpf: Support modules in bpf_program__set_attach_target() API

Support finding kernel targets in kernel modules when using
bpf_program__set_attach_target() API. This brings it up to par with what
libbpf supports when doing declarative SEC()-based target determination.

Some minor internal refactoring was needed to make sure vmlinux BTF can be
loaded before bpf_object's load phase.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20201211215825.3646154-2-andrii@kernel.org

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 9be88a9..6ae748f 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2518,7 +2518,7 @@ static int bpf_object__finalize_btf(struct bpf_object *obj)
        return 0;
 }
 
-static inline bool libbpf_prog_needs_vmlinux_btf(struct bpf_program *prog)
+static bool prog_needs_vmlinux_btf(struct bpf_program *prog)
 {
        if (prog->type == BPF_PROG_TYPE_STRUCT_OPS ||
            prog->type == BPF_PROG_TYPE_LSM)
@@ -2533,37 +2533,43 @@ static inline bool libbpf_prog_needs_vmlinux_btf(struct bpf_program *prog)
        return false;
 }
 
-static int bpf_object__load_vmlinux_btf(struct bpf_object *obj)
+static bool obj_needs_vmlinux_btf(const struct bpf_object *obj)
 {
-       bool need_vmlinux_btf = false;
        struct bpf_program *prog;
-       int i, err;
+       int i;
 
        /* CO-RE relocations need kernel BTF */
        if (obj->btf_ext && obj->btf_ext->core_relo_info.len)
-               need_vmlinux_btf = true;
+               return true;
 
        /* Support for typed ksyms needs kernel BTF */
        for (i = 0; i < obj->nr_extern; i++) {
                const struct extern_desc *ext;
 
                ext = &obj->externs[i];
-               if (ext->type == EXT_KSYM && ext->ksym.type_id) {
-                       need_vmlinux_btf = true;
-                       break;
-               }
+               if (ext->type == EXT_KSYM && ext->ksym.type_id)
+                       return true;
        }
 
        bpf_object__for_each_program(prog, obj) {
                if (!prog->load)
                        continue;
-               if (libbpf_prog_needs_vmlinux_btf(prog)) {
-                       need_vmlinux_btf = true;
-                       break;
-               }
+               if (prog_needs_vmlinux_btf(prog))
+                       return true;
        }
 
-       if (!need_vmlinux_btf)
+       return false;
+}
+
+static int bpf_object__load_vmlinux_btf(struct bpf_object *obj, bool force)
+{
+       int err;
+
+       /* btf_vmlinux could be loaded earlier */
+       if (obj->btf_vmlinux)
+               return 0;
+
+       if (!force && !obj_needs_vmlinux_btf(obj))
                return 0;
 
        obj->btf_vmlinux = libbpf_find_kernel_btf();
@@ -7475,7 +7481,7 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
        }
 
        err = bpf_object__probe_loading(obj);
-       err = err ? : bpf_object__load_vmlinux_btf(obj);
+       err = err ? : bpf_object__load_vmlinux_btf(obj, false);
        err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
        err = err ? : bpf_object__sanitize_and_load_btf(obj);
        err = err ? : bpf_object__sanitize_maps(obj);
@@ -10870,23 +10876,33 @@ int bpf_program__set_attach_target(struct bpf_program *prog,
                                   int attach_prog_fd,
                                   const char *attach_func_name)
 {
-       int btf_id;
+       int btf_obj_fd = 0, btf_id = 0, err;
 
        if (!prog || attach_prog_fd < 0 || !attach_func_name)
                return -EINVAL;
 
-       if (attach_prog_fd)
+       if (prog->obj->loaded)
+               return -EINVAL;
+
+       if (attach_prog_fd) {
                btf_id = libbpf_find_prog_btf_id(attach_func_name,
                                                 attach_prog_fd);
-       else
-               btf_id = libbpf_find_vmlinux_btf_id(attach_func_name,
-                                                   prog->expected_attach_type);
-
-       if (btf_id < 0)
-               return btf_id;
+               if (btf_id < 0)
+                       return btf_id;
+       } else {
+               /* load btf_vmlinux, if not yet */
+               err = bpf_object__load_vmlinux_btf(prog->obj, true);
+               if (err)
+                       return err;
+               err = find_kernel_btf_id(prog->obj, attach_func_name,
+                                        prog->expected_attach_type,
+                                        &btf_obj_fd, &btf_id);
+               if (err)
+                       return err;
+       }
 
        prog->attach_btf_id = btf_id;
-       prog->attach_btf_obj_fd = 0;
+       prog->attach_btf_obj_fd = btf_obj_fd;
        prog->attach_prog_fd = attach_prog_fd;
        return 0;
 }