Advertise a minimum alignment for SharedMemory::Map().

base/shared_memory_unittest.cc

 // Copyright (c) 2012 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 "base/basictypes.h"
 #if defined(OS_MACOSX)
 #include "base/mac/scoped_nsautorelease_pool.h"
 #endif
 #include "base/memory/scoped_ptr.h"
 #include "base/shared_memory.h"
@@ skipping 343 matching lines @@
   options.executable = true;
 
   EXPECT_TRUE(shared_memory.Create(options));
   EXPECT_TRUE(shared_memory.Map(shared_memory.created_size()));
 
   EXPECT_EQ(0, mprotect(shared_memory.memory(), shared_memory.created_size(),
                         PROT_READ | PROT_EXEC));
 }
 #endif
 
+// Map() will return addresses which are aligned to the platform page size, this
+// varies from platform to platform though.  Since we'd like to advertise a
+// minimum alignment that callers can count on, test for it here.
+TEST(SharedMemoryTest, MapMinimumAlignment) {
+  static const int kDataSize = 8192;
+
+  SharedMemory shared_memory;
+  ASSERT_TRUE(shared_memory.CreateAndMapAnonymous(kDataSize));
+  EXPECT_EQ(0U, reinterpret_cast<uintptr_t>(
+      shared_memory.memory()) & (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
+  shared_memory.Close();
+}
+
 #if !defined(OS_IOS)  // iOS does not allow multiple processes.
 
 // On POSIX it is especially important we test shmem across processes,
 // not just across threads.  But the test is enabled on all platforms.
 class SharedMemoryProcessTest : public MultiProcessTest {
  public:
 
   static void CleanUp() {
     SharedMemory memory;
     memory.Delete(s_test_name_);
@@ skipping 54 matching lines @@
   SharedMemoryProcessTest::CleanUp();
 }
 
 MULTIPROCESS_TEST_MAIN(SharedMemoryTestMain) {
   return SharedMemoryProcessTest::TaskTestMain();
 }
 
 #endif  // !OS_IOS
 
 }  // namespace base