Add android_dlwarning() method

This is temporary method intended to use
for a toast message on preview and beta
releases. Will be removed before the
production release.

Bug: http://b/27365747
Change-Id: I39cc716bb82863ae761b6821bcec77cce6db3781
diff --git a/linker/linker_dlwarning.cpp b/linker/linker_dlwarning.cpp
new file mode 100644
index 0000000..f4a3daf
--- /dev/null
+++ b/linker/linker_dlwarning.cpp
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include "linker_dlwarning.h"
+
+#include <strings.h>
+
+#include <string>
+
+static std::string current_msg;
+static std::string old_msg;
+
+void add_dlwarning(const char* sopath, const char* message, const char* value) {
+  if (!current_msg.empty()) {
+    current_msg += '\n';
+  }
+
+  current_msg = current_msg + basename(sopath) + ": " + message;
+
+  if (value != nullptr) {
+    current_msg = current_msg + " \'" + value + "\'";
+  }
+
+}
+
+// Resets the current one (like dlerror but instead of
+// being thread-local it is process-local).
+const char* get_dlwarning() {
+  if (current_msg.empty()) {
+    return nullptr;
+  }
+
+  old_msg = current_msg;
+  current_msg.clear();
+
+  return old_msg.c_str();
+}