Fix for issue 23908 - error message reports the exact error when a native extension fails to load.

runtime/bin/extensions_android.cc

Index: runtime/bin/extensions_android.cc
diff --git a/runtime/bin/extensions_android.cc b/runtime/bin/extensions_android.cc
index 1b7999169d0bcdb309a67e975cd10519eedd6f2a..811c70058638dd574641c418a9cde84aa5a53430 100644
--- a/runtime/bin/extensions_android.cc
+++ b/runtime/bin/extensions_android.cc
@@ -15,15 +15,27 @@ namespace bin {
 const char* kPrecompiledLibraryName = "libprecompiled.so";
 const char* kPrecompiledSymbolName = "_kInstructionsSnapshot";
 
-void* Extensions::LoadExtensionLibrary(const char* library_file) {
-  return dlopen(library_file, RTLD_LAZY);
+Dart_Handle Extensions::LoadExtensionLibrary(const char* library_file,
+                                             void** library_handle) {
+  ASSERT(library_handle != NULL);
+  *library_handle = dlopen(library_file, RTLD_LAZY);
+  if (*library_handle == NULL) {
+    return Dart_NewApiError(dlerror());
+  }
+  return Dart_Null();
 }
 
-void* Extensions::ResolveSymbol(void* lib_handle, const char* symbol) {
+Dart_Handle Extensions::ResolveSymbol(void* lib_handle,
+                                      const char* symbol,
+                                      void** init_function) {
+  ASSERT(init_function != NULL);
   dlerror();
-  void* result = dlsym(lib_handle, symbol);
-  if (dlerror() != NULL) return NULL;
-  return result;
+  *init_function = dlsym(lib_handle, symbol);
+  char* err_str = dlerror();
+  if (err_str != NULL) {
+    return Dart_NewApiError(err_str);

[Søren Gjesse, 2015/10/14 07:00:25]

Drop the temp err_str like above?

[siva, 2015/10/14 18:13:19]

It is not possible to drop the temp err_str, see comment from man pages "Since
the value of the symbol could actually be NULL (so that a NULL return  from 
dlsym()  need  not indicate  an  error),  the  correct way to test for an error
is to call dlerror() to clear any old error conditions,  then  call  dlsym(), 
and then call dlerror() again, saving its return value into a variable, and
check whether this saved value is not NULL"

+  }
+  return Dart_Null();
 }
 
 }  // namespace bin