tls: document package and guard helpers

runtime/internal/clite/tls/tls_gc.go

@@ -1,5 +1,21 @@
 //go:build llgo && !nogc
 
+/*
+ * Copyright (c) 2025 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package tls
 
 import (
@@ -48,6 +64,11 @@ func deregisterSlot[T any](s *slot[T]) {
 
 func (s *slot[T]) rootRange() (start, end c.Pointer) {
 	begin := unsafe.Pointer(s)
-	endPtr := unsafe.Pointer(uintptr(begin) + unsafe.Sizeof(*s))
+	size := unsafe.Sizeof(*s)
+	beginAddr := uintptr(begin)
+	if beginAddr > ^uintptr(0)-size {
+		panic("tls: pointer arithmetic overflow in rootRange")
+	}
+	endPtr := unsafe.Pointer(beginAddr + size)
 	return c.Pointer(begin), c.Pointer(endPtr)
 }