[PATCH v2 2/9] bpf/btf: tracing: Move finding func-proto API and getting func-param API to BTF

["Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Move generic function-proto find API and getting function parameter API
to BTF library code from trace_probe.c. This will avoid redundant efforts
on different feature.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 include/linux/btf.h        |    4 ++++
 kernel/bpf/btf.c           |   45 ++++++++++++++++++++++++++++++++++++++++
 kernel/trace/trace_probe.c |   50 +++++++++++++-------------------------------
 3 files changed, 64 insertions(+), 35 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index cac9f304e27a..98fbbcdd72ec 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -221,6 +221,10 @@ const struct btf_type *
 btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		 u32 *type_size);
 const char *btf_type_str(const struct btf_type *t);
+const struct btf_type *btf_find_func_proto(struct btf *btf,
+					   const char *func_name);
+const struct btf_param *btf_get_func_param(const struct btf_type *func_proto,
+					   s32 *nr);
 
 #define for_each_member(i, struct_type, member)			\
 	for (i = 0, member = btf_type_member(struct_type);	\
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 817204d53372..e015b52956cb 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -1947,6 +1947,51 @@ btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 	return __btf_resolve_size(btf, type, type_size, NULL, NULL, NULL, NULL);
 }
 
+/*
+ * Find a functio proto type by name, and return it.
+ * Return NULL if not found, or return -EINVAL if parameter is invalid.
+ */
+const struct btf_type *btf_find_func_proto(struct btf *btf, const char *func_name)
+{
+	const struct btf_type *t;
+	s32 id;
+
+	if (!btf || !func_name)
+		return ERR_PTR(-EINVAL);
+
+	id = btf_find_by_name_kind(btf, func_name, BTF_KIND_FUNC);
+	if (id <= 0)
+		return NULL;
+
+	/* Get BTF_KIND_FUNC type */
+	t = btf_type_by_id(btf, id);
+	if (!t || !btf_type_is_func(t))
+		return NULL;
+
+	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
+	t = btf_type_by_id(btf, t->type);
+	if (!t || !btf_type_is_func_proto(t))
+		return NULL;
+
+	return t;
+}
+
+/*
+ * Get function parameter with the number of parameters.
+ * This can return NULL if the function has no parameters.
+ */
+const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s32 *nr)
+{
+	if (!func_proto || !nr)
+		return ERR_PTR(-EINVAL);
+
+	*nr = btf_type_vlen(func_proto);
+	if (*nr > 0)
+		return (const struct btf_param *)(func_proto + 1);
+	else
+		return NULL;
+}
+
 static u32 btf_resolved_type_id(const struct btf *btf, u32 type_id)
 {
 	while (type_id < btf->start_id)
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index c68a72707852..cd89fc1ebb42 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -371,47 +371,23 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
 	return NULL;
 }
 
-static const struct btf_type *find_btf_func_proto(const char *funcname)
-{
-	struct btf *btf = traceprobe_get_btf();
-	const struct btf_type *t;
-	s32 id;
-
-	if (!btf || !funcname)
-		return ERR_PTR(-EINVAL);
-
-	id = btf_find_by_name_kind(btf, funcname, BTF_KIND_FUNC);
-	if (id <= 0)
-		return ERR_PTR(-ENOENT);
-
-	/* Get BTF_KIND_FUNC type */
-	t = btf_type_by_id(btf, id);
-	if (!t || !btf_type_is_func(t))
-		return ERR_PTR(-ENOENT);
-
-	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
-	t = btf_type_by_id(btf, t->type);
-	if (!t || !btf_type_is_func_proto(t))
-		return ERR_PTR(-ENOENT);
-
-	return t;
-}
-
 static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,
 						   bool tracepoint)
 {
+	struct btf *btf = traceprobe_get_btf();
 	const struct btf_param *param;
 	const struct btf_type *t;
 
-	if (!funcname || !nr)
+	if (!funcname || !nr || !btf)
 		return ERR_PTR(-EINVAL);
 
-	t = find_btf_func_proto(funcname);
-	if (IS_ERR(t))
+	t = btf_find_func_proto(btf, funcname);
+	if (IS_ERR_OR_NULL(t))
 		return (const struct btf_param *)t;
 
-	*nr = btf_type_vlen(t);
-	param = (const struct btf_param *)(t + 1);
+	param = btf_get_func_param(t, nr);
+	if (IS_ERR_OR_NULL(param))
+		return param;
 
 	/* Hide the first 'data' argument of tracepoint */
 	if (tracepoint) {
@@ -490,8 +466,8 @@ static const struct fetch_type *parse_btf_retval_type(
 	const struct btf_type *t;
 
 	if (btf && ctx->funcname) {
-		t = find_btf_func_proto(ctx->funcname);
-		if (!IS_ERR(t))
+		t = btf_find_func_proto(btf, ctx->funcname);
+		if (!IS_ERR_OR_NULL(t))
 			typestr = type_from_btf_id(btf, t->type);
 	}
 
@@ -500,10 +476,14 @@ static const struct fetch_type *parse_btf_retval_type(
 
 static bool is_btf_retval_void(const char *funcname)
 {
+	struct btf *btf = traceprobe_get_btf();
 	const struct btf_type *t;
 
-	t = find_btf_func_proto(funcname);
-	if (IS_ERR(t))
+	if (!btf)
+		return false;
+
+	t = btf_find_func_proto(btf, funcname);
+	if (IS_ERR_OR_NULL(t))
 		return false;
 
 	return t->type == 0;