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

runtime/bin/extensions_android.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_ANDROID)
 
 #include "bin/extensions.h"
 #include <dlfcn.h>  // NOLINT
 
 
 namespace dart {
 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
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_ANDROID)