[PATCHv4 bpf-next 16/25] libbpf: Add btf_type_is_traceable_func function

[Jiri Olsa <jolsa@kernel.org>]

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>
---
 tools/lib/bpf/libbpf.c          | 54 +++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf_internal.h |  1 +
 2 files changed, 55 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index c6cd6ccb870b..139df8484edb 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -12353,6 +12353,60 @@ 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;
+	}
+}
+
+bool btf_type_is_traceable_func(const struct btf *btf, const struct btf_type *t)
+{
+	const struct btf_type *proto;
+	const struct btf_param *args;
+	__u32 i, nargs;
+	__s64 ret;
+
+	proto = btf_type_by_id(btf, t->type);
+	if (BTF_INFO_KIND(proto->info) != BTF_KIND_FUNC_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/union return argument type. */
+	t = btf__type_by_id(btf, proto->type);
+	while (t && btf_type_is_modifier(t))
+		t = btf__type_by_id(btf, t->type);
+
+	if (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;
+
+		/* No support of struct argument size greater than 16 bytes. */
+		ret = btf__resolve_size(btf, args[i].type);
+		if (ret < 0 || ret > 16)
+			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 4bcb6ca69bb1..1b539c901898 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)
 {
-- 
2.53.0