Refactor BPFTesterCompatibilityDelegate to use AuxHolder instead

sandbox/linux/seccomp-bpf/bpf_tester_compatibility_delegate.h

 // Copyright 2014 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.
 
 #ifndef SANDBOX_LINUX_SECCOMP_BPF_BPF_TESTER_COMPATIBILITY_DELEGATE_H_
 #define SANDBOX_LINUX_SECCOMP_BPF_BPF_TESTER_COMPATIBILITY_DELEGATE_H_
 
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 
 #include "base/memory/scoped_ptr.h"
 #include "sandbox/linux/seccomp-bpf/sandbox_bpf_compatibility_policy.h"
 #include "sandbox/linux/seccomp-bpf/sandbox_bpf_test_runner.h"
 #include "sandbox/linux/tests/sandbox_test_runner.h"
 #include "sandbox/linux/tests/unit_tests.h"
 
 namespace sandbox {
 
+namespace internal {
+
+// Internal helper class to hold a value of type T.
+template <typename T>
+class AuxHolder {
+ public:
+  AuxHolder() : val_() {}
+  T* get() { return &val_; }
+
+ private:
+  T val_;
+};
+
+// Specialization of AuxHolder for void.
+// Returns a null pointer instead of allocating void.
+template <>
+class AuxHolder<void> {
+ public:
+  AuxHolder() {}
+  void* get() { return NULL; }
+};
+
+}  // namespace internal
+
 // This templated class allows building a BPFTesterDelegate from a
 // deprecated-style BPF policy (that is a SyscallEvaluator function pointer,
 // instead of a SandboxBPFPolicy class), specified in |policy_function| and a
 // function pointer to a test in |test_function|.
 // This allows both the policy and the test function to take a pointer to an
 // object of type "Aux" as a parameter. This is used to implement the BPF_TEST
 // macro and should generally not be used directly.
 template <class Aux = void>
 class BPFTesterCompatibilityDelegate : public BPFTesterDelegate {
  public:
   typedef Aux AuxType;
   BPFTesterCompatibilityDelegate(
       void (*test_function)(AuxType*),
       typename CompatibilityPolicy<AuxType>::SyscallEvaluator policy_function)
-      : aux_pointer_for_policy_(NULL),
+      : aux_holder_(),
         test_function_(test_function),
-        policy_function_(policy_function) {
-    // This will be NULL iff AuxType is void.
-    aux_pointer_for_policy_ = NewAux();
-  }
+        policy_function_(policy_function) {}
 
-  virtual ~BPFTesterCompatibilityDelegate() {
-    DeleteAux(aux_pointer_for_policy_);
-  }
+  virtual ~BPFTesterCompatibilityDelegate() {}
 
   virtual scoped_ptr<SandboxBPFPolicy> GetSandboxBPFPolicy() OVERRIDE {
     // The current method is guaranteed to only run in the child process
     // running the test. In this process, the current object is guaranteed
     // to live forever. So it's ok to pass aux_pointer_for_policy_ to
     // the policy, which could in turn pass it to the kernel via Trap().
-    return scoped_ptr<SandboxBPFPolicy>(new CompatibilityPolicy<AuxType>(
-        policy_function_, aux_pointer_for_policy_));
+    return scoped_ptr<SandboxBPFPolicy>(
+        new CompatibilityPolicy<AuxType>(policy_function_, aux_holder_.get()));
   }
 
   virtual void RunTestFunction() OVERRIDE {
     // Run the actual test.
     // The current object is guaranteed to live forever in the child process
     // where this will run.
-    test_function_(aux_pointer_for_policy_);
+    test_function_(aux_holder_.get());
   }
 
  private:
-  // Allocate an object of type Aux. This is specialized to return NULL when
-  // trying to allocate a void.
-  static Aux* NewAux() { return new Aux(); }
-  static void DeleteAux(Aux* aux) { delete aux; }
-
-  AuxType* aux_pointer_for_policy_;
+  internal::AuxHolder<AuxType> aux_holder_;
   void (*test_function_)(AuxType*);
   typename CompatibilityPolicy<AuxType>::SyscallEvaluator policy_function_;
   DISALLOW_COPY_AND_ASSIGN(BPFTesterCompatibilityDelegate);
 };
 
-// Specialization of NewAux that returns NULL;
-template <>
-void* BPFTesterCompatibilityDelegate<void>::NewAux();
-template <>
-void BPFTesterCompatibilityDelegate<void>::DeleteAux(void* aux);
-
 }  // namespace sandbox
 
 #endif  // SANDBOX_LINUX_SECCOMP_BPF_BPF_TESTER_COMPATIBILITY_DELEGATE_H_