Sync linker with internal branch

This change includes dlwarning implementation and
the compatibility greylist for apps targeting pre-N.

Change-Id: Ibf02a07cc58cbbb1a5aef4ac34558c5d43e4305f
Test: Run bionic-unit-tests --gtest_filter=dl*:Dl*
diff --git a/linker/linker_dlwarning.cpp b/linker/linker_dlwarning.cpp
new file mode 100644
index 0000000..c53ad66
--- /dev/null
+++ b/linker/linker_dlwarning.cpp
@@ -0,0 +1,47 @@
+/*
+ * 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;
+
+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).
+void get_dlwarning(void* obj, void (*f)(void*, const char*)) {
+  if (current_msg.empty()) {
+    f(obj, nullptr);
+  } else {
+    std::string msg = current_msg;
+    current_msg.clear();
+    f(obj, msg.c_str());
+  }
+}