From ce44166c737b6737c3a0820bef10b074a5e36cf8 Mon Sep 17 00:00:00 2001
From: Dmitriy Ivanov <dimitry@google.com>
Date: Tue, 17 Jun 2014 15:56:38 -0700
Subject: [PATCH] Fix weak function lookups

 * Linker now correctly resolves function defined
   with __attribute__((weak)).

Bug: https://code.google.com/p/android/issues/detail?id=70206
Change-Id: I82efb905676c25fefb1b11a13f5fecb0f1384657
---
 linker/dlfcn.cpp                   |  2 +-
 tests/dlfcn_test.cpp               | 12 ++++++++++++
 tests/libs/Android.mk              | 12 ++++++++++++
 tests/libs/dlsym_weak_function.cpp | 20 ++++++++++++++++++++
 4 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 tests/libs/dlsym_weak_function.cpp

diff --git a/linker/dlfcn.cpp b/linker/dlfcn.cpp
index 6d63ad646..0b60ef5f4 100644
--- a/linker/dlfcn.cpp
+++ b/linker/dlfcn.cpp
@@ -118,7 +118,7 @@ void* dlsym(void* handle, const char* symbol) {
   if (sym != NULL) {
     unsigned bind = ELF_ST_BIND(sym->st_info);
 
-    if (bind == STB_GLOBAL && sym->st_shndx != 0) {
+    if ((bind == STB_GLOBAL || bind == STB_WEAK) && sym->st_shndx != 0) {
       return reinterpret_cast<void*>(sym->st_value + found->load_bias);
     }
 
diff --git a/tests/dlfcn_test.cpp b/tests/dlfcn_test.cpp
index 49cbb7d17..8b8918326 100644
--- a/tests/dlfcn_test.cpp
+++ b/tests/dlfcn_test.cpp
@@ -254,6 +254,18 @@ TEST(dlfcn, rtld_next_known_symbol) {
   ASSERT_TRUE(addr != NULL);
 }
 
+TEST(dlfcn, dlsym_weak_func) {
+  dlerror();
+  void* handle = dlopen("libtest_dlsym_weak_func.so",RTLD_NOW);
+  ASSERT_TRUE(handle != NULL);
+
+  int (*weak_func)();
+  weak_func = reinterpret_cast<int (*)()>(dlsym(handle, "weak_func"));
+  ASSERT_TRUE(weak_func != NULL) << "dlerror: " << dlerror();
+  EXPECT_EQ(42, weak_func());
+  dlclose(handle);
+}
+
 TEST(dlfcn, dlopen_symlink) {
   void* handle1 = dlopen("libdlext_test.so", RTLD_NOW);
   void* handle2 = dlopen("libdlext_test_v2.so", RTLD_NOW);
diff --git a/tests/libs/Android.mk b/tests/libs/Android.mk
index e75582dbc..67ea562b3 100644
--- a/tests/libs/Android.mk
+++ b/tests/libs/Android.mk
@@ -103,3 +103,15 @@ include $(TEST_PATH)/Android.build.mk
 build_type := host
 include $(TEST_PATH)/Android.build.mk
 
+# -----------------------------------------------------------------------------
+# Library with weak function
+# -----------------------------------------------------------------------------
+libtest_dlsym_weak_func_src_files := \
+    dlsym_weak_function.cpp
+
+module := libtest_dlsym_weak_func
+build_target := SHARED_LIBRARY
+build_type := target
+include $(TEST_PATH)/Android.build.mk
+build_type := host
+include $(TEST_PATH)/Android.build.mk
diff --git a/tests/libs/dlsym_weak_function.cpp b/tests/libs/dlsym_weak_function.cpp
new file mode 100644
index 000000000..e38f2b886
--- /dev/null
+++ b/tests/libs/dlsym_weak_function.cpp
@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+extern "C" int __attribute__((weak)) weak_func() {
+  return 42;
+}
+