Linker: Do not require JNI_OnLoad in ModernLinker loads.

base/android/linker/modern_linker_jni.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This is the version of the Android-specific Chromium linker that uses
 // the Android M and later system linker to load libraries.
 
 // This source code *cannot* depend on anything from base/ or the C++
 // STL, to keep the final library small, and avoid ugly dependency issues.
 
@@ skipping 335 matching lines @@
 // so that the Android Package Manager doesn't extract the library into
 // /data/app-lib.
 //
 // If |dlopen_ext_path| contains no "!/" separator then android_dlopen_ext()
 // assumes that it is a normal path to a standalone library file.
 //
 // Loading the library will also call its JNI_OnLoad() method, which
 // shall register its methods. Note that lazy native method resolution
 // will _not_ work after this, because Dalvik uses the system's dlsym()
 // which won't see the new library, so explicit registration is mandatory.
-// Load a library with the chromium linker. This will also call its
-// JNI_OnLoad() method, which shall register its methods. Note that
-// lazy native method resolution will _not_ work after this, because
-// Dalvik uses the system's dlsym() which won't see the new library,
-// so explicit registration is mandatory.
 //
 // |env| is the current JNI environment handle.
 // |clazz| is the static class handle for org.chromium.base.Linker,
 // and is ignored here.
 // |dlopen_ext_path| is the library identifier (e.g. libfoo.so).
 // |load_address| is an explicit load address.
 // |relro_path| is the path to the file into which RELRO data is held.
 // |lib_info_obj| is a LibInfo handle used to communicate information
 // with the Java side.
 // Return true on success.
@@ skipping 58 matching lines @@
   size_t min_vaddr = 0;
   if (!GetLibraryLoadSize(addr, &load_size, &min_vaddr)) {
     LOG_ERROR("Unable to find size for load at %p", addr);
     return false;
   }
   if (!ResizeReservedAddressSpace(addr, size, load_size, min_vaddr)) {
     LOG_ERROR("Unable to resize reserved address mapping");
     return false;
   }
 
-  // Locate and then call the loaded library's JNI_OnLoad() function. Check
-  // that it returns a usable JNI version.
+  // Locate and if found then call the loaded library's JNI_OnLoad() function.
   using JNI_OnLoadFunctionPtr = int (*)(void* vm, void* reserved);
   auto jni_onload =
       reinterpret_cast<JNI_OnLoadFunctionPtr>(dlsym(handle, "JNI_OnLoad"));
-  if (jni_onload == nullptr) {
-    LOG_ERROR("dlsym: JNI_OnLoad: %s", dlerror());
-    return false;
-  }
-
-  int jni_version = (*jni_onload)(s_java_vm, nullptr);
-  if (jni_version < JNI_VERSION_1_4) {
-    LOG_ERROR("JNI version is invalid: %d", jni_version);
-    return false;
+  if (jni_onload != nullptr) {
+    // Check that JNI_OnLoad returns a usable JNI version.
+    int jni_version = (*jni_onload)(s_java_vm, nullptr);
+    if (jni_version < JNI_VERSION_1_4) {
+      LOG_ERROR("JNI version is invalid: %d", jni_version);
+      return false;
+    }
   }
 
   // Release mapping before returning so that we do not unmap reserved space.
   mapping.Release();
 
   // Note the load address and load size in the supplied libinfo object.
   const size_t cast_addr = reinterpret_cast<size_t>(addr);
   s_lib_info_fields.SetLoadInfo(env, lib_info_obj, cast_addr, load_size);
 
   LOG_INFO("Success loading library %s", dlopen_library_path.c_str());
@@ skipping 148 matching lines @@
                        kNativeMethods,
                        sizeof(kNativeMethods) / sizeof(kNativeMethods[0]));
 
   // Record the Java VM handle.
   s_java_vm = vm;
 
   return true;
 }
 
 }  // namespace chromium_android_linker