diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 824bb61..33ee8f1 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -628,9 +628,9 @@ function _drupal_request_initialize() {
  * configuration. For example, a module 'foo' may legally be located
  * in any of these three places:
  *
- * core/modules/foo/foo.module
- * modules/foo/foo.module
- * sites/example.com/modules/foo/foo.module
+ * core/modules/foo/foo.info.yml
+ * modules/foo/foo.info.yml
+ * sites/example.com/modules/foo/foo.info.yml
  *
  * Calling drupal_get_filename('module', 'foo') will give you one of
  * the above, depending on where the module is located.
@@ -671,7 +671,7 @@ function drupal_get_filename($type, $name, $filename = NULL) {
     // Retrieve the current module list (derived from the service container).
     if ($type == 'module' && \Drupal::hasService('module_handler')) {
       foreach (\Drupal::moduleHandler()->getModuleList() as $module_name => $module) {
-        $files[$type][$module_name] = $module->getExtensionPathname();
+        $files[$type][$module_name] = $module->getPathname();
       }
     }
     // If still unknown, retrieve the file list prepared in state by
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 5331e95..3634974 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -492,7 +492,7 @@ function install_begin_request(&$install_state) {
   $module_handler = \Drupal::moduleHandler();
   if (!$module_handler->moduleExists('system')) {
     // Override the module list with a minimal set of modules.
-    \Drupal::moduleHandler()->add('system', 'core/modules/system');
+    $module_handler->add('system', 'core/modules/system');
   }
   // After setting up a custom and finite module list in a custom low-level
   // bootstrap like here, ensure to use ModuleHandler::loadAll() so that
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index c4f070a..054fa0c 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -81,7 +81,7 @@ class DrupalKernel implements DrupalKernelInterface, TerminableInterface {
   protected $newModuleList;
 
   /**
-   * An array of module Extension objects.
+   * List of available modules and installation profiles.
    *
    * @var \Drupal\Core\Extension\Extension[]
    */
@@ -499,7 +499,7 @@ protected function buildContainer() {
     $container = $this->getContainerBuilder();
     $container->set('kernel', $this);
     $container->setParameter('container.service_providers', $this->serviceProviderClasses);
-    $container->setParameter('container.modules', $this->getModules());
+    $container->setParameter('container.modules', $this->getModulesParameter());
 
     // Get a list of namespaces and put it onto the container.
     $namespaces = $this->getModuleNamespaces($this->getModuleFileNames());
@@ -643,15 +643,19 @@ protected function storage() {
   }
 
   /**
-   * Returns a list of enabled modules.
+   * Returns an array of Extension class parameters for all enabled modules.
    *
-   * @return \Drupal\Core\Extension\Extension[]
+   * @return array
    */
-  protected function getModules() {
+  protected function getModulesParameter() {
     $extensions = array();
-    foreach ($this->moduleList as $module => $weight) {
-      if ($data = $this->moduleData($module)) {
-        $extensions[$module] = json_encode($data);
+    foreach ($this->moduleList as $name => $weight) {
+      if ($data = $this->moduleData($name)) {
+        $extensions[$name] = array(
+          'type' => $data->getType(),
+          'pathname' => $data->getPathname(),
+          'filename' => $data->getExtensionFilename(),
+        );
       }
     }
     return $extensions;
diff --git a/core/lib/Drupal/Core/Extension/Extension.php b/core/lib/Drupal/Core/Extension/Extension.php
index 1a6b8f8..cc21c53 100644
--- a/core/lib/Drupal/Core/Extension/Extension.php
+++ b/core/lib/Drupal/Core/Extension/Extension.php
@@ -10,7 +10,7 @@
 /**
  * Defines an extension (file) object.
  */
-class Extension implements \Serializable, \JsonSerializable {
+class Extension implements \Serializable {
 
   /**
    * The type of the extension (e.g., 'module').
@@ -29,7 +29,7 @@ class Extension implements \Serializable, \JsonSerializable {
   /**
    * The filename of the main extension file (e.g., 'node.module').
    *
-   * @var string
+   * @var string|null
    */
   protected $filename;
 
@@ -116,6 +116,15 @@ public function getExtensionPathname() {
   }
 
   /**
+   * Returns the name of the main extension file, if any.
+   *
+   * @return string|null
+   */
+  public function getExtensionFilename() {
+    return $this->filename;
+  }
+
+  /**
    * Loads the main extension file, if any.
    *
    * @return bool
@@ -197,15 +206,4 @@ public function unserialize($data) {
     }
   }
 
-  /**
-   * Implements \JsonSerializable::jsonSerialize().
-   */
-  public function jsonSerialize() {
-    return array(
-      'type' => $this->type,
-      'pathname' => $this->pathname,
-      'filename' => $this->filename,
-    );
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Extension/ModuleHandler.php b/core/lib/Drupal/Core/Extension/ModuleHandler.php
index a1e05fc..003486f 100644
--- a/core/lib/Drupal/Core/Extension/ModuleHandler.php
+++ b/core/lib/Drupal/Core/Extension/ModuleHandler.php
@@ -67,8 +67,8 @@ class ModuleHandler implements ModuleHandlerInterface {
    *
    * @param array $module_list
    *   An associative array whose keys are the names of installed modules and
-   *   whose values are JSON-encoded Extension class parameters. This is
-   *   normally the %container.modules% parameter being set up by DrupalKernel.
+   *   whose values are Extension class parameters. This is normally the
+   *   %container.modules% parameter being set up by DrupalKernel.
    *
    * @see \Drupal\Core\DrupalKernel
    * @see \Drupal\Core\CoreServiceProvider
@@ -76,8 +76,7 @@ class ModuleHandler implements ModuleHandlerInterface {
   public function __construct(array $module_list = array()) {
     $this->moduleList = array();
     foreach ($module_list as $name => $module) {
-      $module = json_decode($module, TRUE);
-      $this->moduleList[$name] = new Extension($module['type'], $module['pathname'], $module['extensionFilename']);
+      $this->moduleList[$name] = new Extension($module['type'], $module['pathname'], $module['filename']);
     }
   }
 
@@ -142,9 +141,9 @@ public function setModuleList(array $module_list = array()) {
   }
 
   public function add($name, $path) {
-    $info = "$path/$name.info.yml";
-    $file = file_exists($path . "/$name.module") ? "$name.module" : NULL;
-    $this->moduleList[$name] = new Extension('module', $info, $file);
+    $pathname = "$path/$name.info.yml";
+    $filename = file_exists($path . "/$name.module") ? "$name.module" : NULL;
+    $this->moduleList[$name] = new Extension('module', $pathname, $filename);
     $this->resetImplementations();
   }
 
@@ -595,9 +594,9 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
           }
           else {
             $module_path = drupal_get_path('module', $name);
-            $module_info = "$module_path/$name.info.yml";
-            $module_file = file_exists($module_path . "/$name.module") ? "$name.module" : NULL;
-            $module_filenames[$name] = new Extension('module', $module_info, $module_file);
+            $pathname = "$module_path/$name.info.yml";
+            $filename = file_exists($module_path . "/$name.module") ? "$name.module" : NULL;
+            $module_filenames[$name] = new Extension('module', $pathname, $filename);
           }
         }
 
diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index b75f3fe..9b6e9cc 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -552,7 +552,7 @@ function simpletest_classloader_register() {
     $extensions = array();
     foreach ($types as $type) {
       foreach ($listing->scan($type, TRUE) as $name => $file) {
-        $extensions[$type][$name] = $file->getExtensionPathname();
+        $extensions[$type][$name] = $file->getPathname();
       }
     }
     \Drupal::cache()->set($cid, $extensions);
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index c633c9d..e58c1cf 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1463,7 +1463,7 @@ function system_rebuild_module_data() {
       $module->weight = isset($installed_modules[$name]) ? $installed_modules[$name] : 0;
       $module->status = (int) isset($installed_modules[$name]);
       $module->schema_version = SCHEMA_UNINSTALLED;
-      $files[$name] = $module->getExtensionPathname() ?: $module->getPathname();
+      $files[$name] = $module->getPathname();
     }
     $modules = \Drupal::moduleHandler()->buildModuleDependencies($modules);
     $modules_cache = $modules;