libbpf: Add btf_type_is_traceable_func function

Adding btf_type_is_traceable_func function to perform same checks
as the kernel's btf_distill_func_proto function to prevent attachment
on some of the functions.

Exporting the function via libbpf_internal.h because it will be used
by benchmark test in following changes.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20260606123955.345967-20-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 80 insertions, 0 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 5bdaa5eb1f50..42f0efd70327 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -12450,6 +12450,85 @@ static int attach_uprobe_multi(const struct bpf_program *prog, long cookie, stru
 	return ret;
 }
 
+#define MAX_BPF_FUNC_ARGS 12
+
+static bool btf_type_is_modifier(const struct btf_type *t)
+{
+	switch (BTF_INFO_KIND(t->info)) {
+	case BTF_KIND_TYPEDEF:
+	case BTF_KIND_VOLATILE:
+	case BTF_KIND_CONST:
+	case BTF_KIND_RESTRICT:
+	case BTF_KIND_TYPE_TAG:
+		return true;
+	default:
+		return false;
+	}
+}
+
+#define MAX_RESOLVE_DEPTH 32
+
+static int btf_get_type_size(const struct btf *btf, __u32 type_id,
+			     const struct btf_type **ret_type)
+{
+	const struct btf_type *t;
+	int i;
+
+	*ret_type = btf__type_by_id(btf, 0);
+	if (!type_id)
+		return 0;
+	t = btf__type_by_id(btf, type_id);
+	for (i = 0; i < MAX_RESOLVE_DEPTH && t && btf_type_is_modifier(t); i++)
+		t = btf__type_by_id(btf, t->type);
+	if (!t || i == MAX_RESOLVE_DEPTH)
+		return -EINVAL;
+	*ret_type = t;
+	if (btf_is_ptr(t))
+		return btf__pointer_size(btf);
+	if (btf_is_int(t) || btf_is_any_enum(t) || btf_is_struct(t) || btf_is_union(t))
+		return t->size;
+	return -EINVAL;
+}
+
+bool btf_type_is_traceable_func(const struct btf *btf, const struct btf_type *t)
+{
+	const struct btf_param *args;
+	const struct btf_type *proto;
+	__u32 i, nargs;
+	int ret;
+
+	if (!btf_is_func(t))
+		return false;
+	proto = btf__type_by_id(btf, t->type);
+	if (!proto || !btf_is_func_proto(proto))
+		return false;
+
+	args = (const struct btf_param *)(proto + 1);
+	nargs = btf_vlen(proto);
+	if (nargs > MAX_BPF_FUNC_ARGS)
+		return false;
+
+	/* No support for struct return type. */
+	ret = btf_get_type_size(btf, proto->type, &t);
+	if (ret < 0 || btf_is_struct(t) || btf_is_union(t))
+		return false;
+
+	for (i = 0; i < nargs; i++) {
+		/* No support for variable args. */
+		if (i == nargs - 1 && args[i].type == 0)
+			return false;
+		ret = btf_get_type_size(btf, args[i].type, &t);
+		/* No support of struct argument size greater than 16 bytes. */
+		if (ret < 0 || ret > 16)
+			return false;
+		/* No support for void argument. */
+		if (ret == 0)
+			return false;
+	}
+
+	return true;
+}
+
 static inline int add_uprobe_event_legacy(const char *probe_name, bool retprobe,
 					  const char *binary_path, size_t offset)
 {
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 7d93c6c01d60..04cd303fb5a8 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -250,6 +250,7 @@ const struct btf_type *skip_mods_and_typedefs(const struct btf *btf, __u32 id, _
 const struct btf_header *btf_header(const struct btf *btf);
 void btf_set_base_btf(struct btf *btf, const struct btf *base_btf);
 int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **id_map);
+bool btf_type_is_traceable_func(const struct btf *btf, const struct btf_type *t);
 
 static inline enum btf_func_linkage btf_func_linkage(const struct btf_type *t)
 {