Fix dlsym(handle_of_main_executable, ...)

According to man dlopen(3) and posix docs in the case when si is handle
  of the main executable we need to search not only in the executable and its
  dependencies but also in all libraries loaded with RTLD_GLOBAL.

  see also: http://pubs.opengroup.org/onlinepubs/9699919799/functions/dlopen.html

Bug: http://b/21528224
Bug: http://b/17512583
Bug: https://code.google.com/p/android/issues/detail?id=173822
Change-Id: Ib2801367ba48b6f3704da89a6d9f5e6911430013
(cherry picked from commit f439b5a3186ca0fef1092f45770abc716da9d87a)

linker/linker.cpp

@@ -963,6 +963,17 @@ static const ElfW(Sym)* dlsym_handle_lookup(soinfo* root, soinfo* skip_until,
 // This is used by dlsym(3).  It performs symbol lookup only within the
 // specified soinfo object and its dependencies in breadth first order.
 const ElfW(Sym)* dlsym_handle_lookup(soinfo* si, soinfo** found, const char* name) {
+  // According to man dlopen(3) and posix docs in the case when si is handle
+  // of the main executable we need to search not only in the executable and its
+  // dependencies but also in all libraries loaded with RTLD_GLOBAL.
+  //
+  // Since RTLD_GLOBAL is always set for the main executable and all dt_needed shared
+  // libraries and they are loaded in breath-first (correct) order we can just execute
+  // dlsym(RTLD_DEFAULT, ...); instead of doing two stage lookup.
+  if (si == somain) {
+    return dlsym_linear_lookup(name, found, nullptr, RTLD_DEFAULT);
+  }
+
   SymbolName symbol_name(name);
   return dlsym_handle_lookup(si, nullptr, found, symbol_name);
 }

tests/dlfcn_test.cpp

@@ -145,13 +145,28 @@ TEST(dlfcn, dlsym_from_sofile_with_preload) {
   dlclose(preload);
 }
 
+TEST(dlfcn, dlsym_handle_global_sym) {
+  // check that we do not look into global group
+  // when looking up symbol by handle
+  void* handle = dlopen("libtest_empty.so", RTLD_NOW);
+  dlopen("libtest_with_dependency.so", RTLD_NOW | RTLD_GLOBAL);
+  void* sym = dlsym(handle, "getRandomNumber");
+  ASSERT_TRUE(sym == nullptr);
+  ASSERT_SUBSTR("undefined symbol: getRandomNumber", dlerror());
+
+  sym = dlsym(handle, "DlSymTestFunction");
+  ASSERT_TRUE(sym == nullptr);
+  ASSERT_SUBSTR("undefined symbol: DlSymTestFunction", dlerror());
+  dlclose(handle);
+}
+
 TEST(dlfcn, dlsym_with_dependencies) {
   void* handle = dlopen("libtest_with_dependency.so", RTLD_NOW);
-  ASSERT_TRUE(handle != NULL);
+  ASSERT_TRUE(handle != nullptr);
   dlerror();
   // This symbol is in DT_NEEDED library.
   void* sym = dlsym(handle, "getRandomNumber");
-  ASSERT_TRUE(sym != NULL);
+  ASSERT_TRUE(sym != nullptr) << dlerror();
   int (*fn)(void);
   fn = reinterpret_cast<int (*)(void)>(sym);
   EXPECT_EQ(4, fn());
@@ -583,6 +598,15 @@ TEST(dlfcn, dlopen_check_rtld_global) {
   // RTLD_GLOBAL implies RTLD_NODELETE, let's check that
   void* sym_after_dlclose = dlsym(RTLD_DEFAULT, "dlopen_testlib_simple_func");
   ASSERT_EQ(sym, sym_after_dlclose);
+
+  // Check if dlsym() for main program's handle searches RTLD_GLOBAL
+  // shared libraries after symbol was not found in the main executable
+  // and dependent libraries.
+  void* handle_for_main_executable = dlopen(nullptr, RTLD_NOW);
+  sym = dlsym(handle_for_main_executable, "dlopen_testlib_simple_func");
+  ASSERT_TRUE(sym != nullptr) << dlerror();
+
+  dlclose(handle_for_main_executable);
 }
 
 // libtest_with_dependency_loop.so -> libtest_with_dependency_loop_a.so ->

tests/libs/Android.mk

@@ -404,6 +404,14 @@ libtest_dlsym_from_this_grandchild_src_files := dlsym_from_this_symbol2.cpp
 module := libtest_dlsym_from_this_grandchild
 include $(LOCAL_PATH)/Android.build.testlib.mk
 
+# -----------------------------------------------------------------------------
+# Empty library
+# -----------------------------------------------------------------------------
+libtest_empty_src_files := empty.cpp
+
+module := libtest_empty
+include $(LOCAL_PATH)/Android.build.testlib.mk
+
 # -----------------------------------------------------------------------------
 # Library with weak undefined function
 # -----------------------------------------------------------------------------