tracing/probes: Move finding func-proto API and getting func-param API to trace_btf

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.

Link: https://lore.kernel.org/all/169272155255.160970.719426926348706349.stgit@devnote2/

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 53 insertions, 0 deletions

diff --git a/kernel/trace/trace_btf.c b/kernel/trace/trace_btf.c
new file mode 100644
index 000000000000..d70b8ee9af37
--- /dev/null
+++ b/kernel/trace/trace_btf.c
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/btf.h>
+#include <linux/kernel.h>
+
+#include "trace_btf.h"
+
+/*
+ * Find a function proto type by name, and return the btf_type with its btf
+ * in *@btf_p. Return NULL if not found.
+ * Note that caller has to call btf_put(*@btf_p) after using the btf_type.
+ */
+const struct btf_type *btf_find_func_proto(const char *func_name, struct btf **btf_p)
+{
+	const struct btf_type *t;
+	s32 id;
+
+	id = bpf_find_btf_id(func_name, BTF_KIND_FUNC, btf_p);
+	if (id < 0)
+		return NULL;
+
+	/* Get BTF_KIND_FUNC type */
+	t = btf_type_by_id(*btf_p, id);
+	if (!t || !btf_type_is_func(t))
+		goto err;
+
+	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
+	t = btf_type_by_id(*btf_p, t->type);
+	if (!t || !btf_type_is_func_proto(t))
+		goto err;
+
+	return t;
+err:
+	btf_put(*btf_p);
+	return NULL;
+}
+
+/*
+ * Get function parameter with the number of parameters.
+ * This can return NULL if the function has no parameters.
+ * It can return -EINVAL if the @func_proto is not a function proto type.
+ */
+const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s32 *nr)
+{
+	if (!btf_type_is_func_proto(func_proto))
+		return ERR_PTR(-EINVAL);
+
+	*nr = btf_type_vlen(func_proto);
+	if (*nr > 0)
+		return (const struct btf_param *)(func_proto + 1);
+	else
+		return NULL;
+}
+