Make sure that ScratchBuffer::Allocate() always return 8-byte aligned address.

mojo/public/cpp/bindings/tests/buffer_unittest.cc

 // 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.
 
 #include <limits>
 
 #include "mojo/public/cpp/bindings/buffer.h"
 #include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
 #include "mojo/public/cpp/bindings/lib/fixed_buffer.h"
 #include "mojo/public/cpp/bindings/lib/scratch_buffer.h"
@@ skipping 35 matching lines @@
 
   // And a request so large it will fail.
   void* fail = buf.Allocate(std::numeric_limits<size_t>::max() - 1024u);
   EXPECT_TRUE(!fail);
 
   // And a request so large it will overflow and fail.
   void* overflow = buf.Allocate(std::numeric_limits<size_t>::max() - 12u);
   EXPECT_TRUE(!overflow);
 }
 
+TEST(ScratchBufferTest, Alignment) {
+  Environment env;
+
+  internal::ScratchBuffer buf;
+  // Test that small allocations on the stack are aligned properly.
+  void* small = buf.Allocate(1);
+  EXPECT_EQ(0, reinterpret_cast<ptrdiff_t>(small) % 8);
+  small = buf.Allocate(2);
+  EXPECT_EQ(0, reinterpret_cast<ptrdiff_t>(small) % 8);
+
+  // Test that large allocations on the heap are aligned properly.
+  void* large = buf.Allocate(10*1024);
+  EXPECT_EQ(0, reinterpret_cast<ptrdiff_t>(large) % 8);
+  large = buf.Allocate(100*1024);
+  EXPECT_EQ(0, reinterpret_cast<ptrdiff_t>(large) % 8);
+}
+
 // Tests that Buffer::current() returns the correct value.
 TEST(ScratchBufferTest, Stacked) {
   Environment env;
 
   EXPECT_FALSE(Buffer::current());
 
   {
     internal::ScratchBuffer a;
     EXPECT_EQ(&a, Buffer::current());
 
@@ skipping 73 matching lines @@
 
   // A lot too large, leading to possible integer overflow.
   EXPECT_EQ(reinterpret_cast<void*>(0),
             buf.Allocate(std::numeric_limits<size_t>::max() - 8u));
 }
 #endif
 
 }  // namespace
 }  // namespace test
 }  // namespace mojo