runtime/mem_map_test.cc - platform/art - Gitiles

 /*
  * Copyright (C) 2013 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "mem_map.h"

 #include <memory>

 #include <valgrind.h>

 #include "gtest/gtest.h"

 namespace art {

 class MemMapTest : public testing::Test {
  public:
   static uint8_t* BaseBegin(MemMap* mem_map) {
     return reinterpret_cast<uint8_t*>(mem_map->base_begin_);
   }
   static size_t BaseSize(MemMap* mem_map) {
     return mem_map->base_size_;
   }

   static void RemapAtEndTest(bool low_4gb) {
     std::string error_msg;
     // Cast the page size to size_t.
     const size_t page_size = static_cast<size_t>(kPageSize);
     // Map a two-page memory region.
     MemMap* m0 = MemMap::MapAnonymous("MemMapTest_RemapAtEndTest_map0",
                                       nullptr,
                                       2 * page_size,
                                       PROT_READ | PROT_WRITE,
                                       low_4gb,
                                       false,
                                       &error_msg);
     // Check its state and write to it.
     uint8_t* base0 = m0->Begin();
     ASSERT_TRUE(base0 != nullptr) << error_msg;
     size_t size0 = m0->Size();
     EXPECT_EQ(m0->Size(), 2 * page_size);
     EXPECT_EQ(BaseBegin(m0), base0);
     EXPECT_EQ(BaseSize(m0), size0);
     memset(base0, 42, 2 * page_size);
     // Remap the latter half into a second MemMap.
     MemMap* m1 = m0->RemapAtEnd(base0 + page_size,
                                 "MemMapTest_RemapAtEndTest_map1",
                                 PROT_READ | PROT_WRITE,
                                 &error_msg);
     // Check the states of the two maps.
     EXPECT_EQ(m0->Begin(), base0) << error_msg;
     EXPECT_EQ(m0->Size(), page_size);
     EXPECT_EQ(BaseBegin(m0), base0);
     EXPECT_EQ(BaseSize(m0), page_size);
     uint8_t* base1 = m1->Begin();
     size_t size1 = m1->Size();
     EXPECT_EQ(base1, base0 + page_size);
     EXPECT_EQ(size1, page_size);
     EXPECT_EQ(BaseBegin(m1), base1);
     EXPECT_EQ(BaseSize(m1), size1);
     // Write to the second region.
     memset(base1, 43, page_size);
     // Check the contents of the two regions.
     for (size_t i = 0; i < page_size; ++i) {
       EXPECT_EQ(base0[i], 42);
     }
     for (size_t i = 0; i < page_size; ++i) {
       EXPECT_EQ(base1[i], 43);
     }
     // Unmap the first region.
     delete m0;
     // Make sure the second region is still accessible after the first
     // region is unmapped.
     for (size_t i = 0; i < page_size; ++i) {
       EXPECT_EQ(base1[i], 43);
     }
     delete m1;
   }

   void CommonInit() {
     MemMap::Init();
   }

 #if defined(__LP64__) && !defined(__x86_64__)
   static uintptr_t GetLinearScanPos() {
     return MemMap::next_mem_pos_;
   }
 #endif
 };

 #if defined(__LP64__) && !defined(__x86_64__)

 #ifdef __BIONIC__
 extern uintptr_t CreateStartPos(uint64_t input);
 #endif

 TEST_F(MemMapTest, Start) {
   CommonInit();
   uintptr_t start = GetLinearScanPos();
   EXPECT_LE(64 * KB, start);
   EXPECT_LT(start, static_cast<uintptr_t>(ART_BASE_ADDRESS));
 #ifdef __BIONIC__
   // Test a couple of values. Make sure they are different.
   uintptr_t last = 0;
   for (size_t i = 0; i < 100; ++i) {
     uintptr_t random_start = CreateStartPos(i * kPageSize);
     EXPECT_NE(last, random_start);
     last = random_start;
   }

   // Even on max, should be below ART_BASE_ADDRESS.
   EXPECT_LT(CreateStartPos(~0), static_cast<uintptr_t>(ART_BASE_ADDRESS));
 #endif
   // End of test.
 }
 #endif

 TEST_F(MemMapTest, MapAnonymousEmpty) {
   CommonInit();
   std::string error_msg;
   std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousEmpty",
                                                    nullptr,
                                                    0,
                                                    PROT_READ,
                                                    false,
                                                    false,
                                                    &error_msg));
   ASSERT_TRUE(map.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());
   map.reset(MemMap::MapAnonymous("MapAnonymousEmpty",
                                  nullptr,
                                  kPageSize,
                                  PROT_READ | PROT_WRITE,
                                  false,
                                  false,
                                  &error_msg));
   ASSERT_TRUE(map.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());
 }

 #ifdef __LP64__
 TEST_F(MemMapTest, MapAnonymousEmpty32bit) {
   CommonInit();
   std::string error_msg;
   std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousEmpty",
                                                    nullptr,
                                                    kPageSize,
                                                    PROT_READ | PROT_WRITE,
                                                    true,
                                                    false,
                                                    &error_msg));
   ASSERT_TRUE(map.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());
   ASSERT_LT(reinterpret_cast<uintptr_t>(BaseBegin(map.get())), 1ULL << 32);
 }
 #endif

 TEST_F(MemMapTest, MapAnonymousExactAddr) {
   CommonInit();
   std::string error_msg;
   // Map at an address that should work, which should succeed.
   std::unique_ptr<MemMap> map0(MemMap::MapAnonymous("MapAnonymous0",
                                                     reinterpret_cast<uint8_t*>(ART_BASE_ADDRESS),
                                                     kPageSize,
                                                     PROT_READ | PROT_WRITE,
                                                     false,
                                                     false,
                                                     &error_msg));
   ASSERT_TRUE(map0.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());
   ASSERT_TRUE(map0->BaseBegin() == reinterpret_cast<void*>(ART_BASE_ADDRESS));
   // Map at an unspecified address, which should succeed.
   std::unique_ptr<MemMap> map1(MemMap::MapAnonymous("MapAnonymous1",
                                                     nullptr,
                                                     kPageSize,
                                                     PROT_READ | PROT_WRITE,
                                                     false,
                                                     false,
                                                     &error_msg));
   ASSERT_TRUE(map1.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());
   ASSERT_TRUE(map1->BaseBegin() != nullptr);
   // Attempt to map at the same address, which should fail.
   std::unique_ptr<MemMap> map2(MemMap::MapAnonymous("MapAnonymous2",
                                                     reinterpret_cast<uint8_t*>(map1->BaseBegin()),
                                                     kPageSize,
                                                     PROT_READ | PROT_WRITE,
                                                     false,
                                                     false,
                                                     &error_msg));
   ASSERT_TRUE(map2.get() == nullptr) << error_msg;
   ASSERT_TRUE(!error_msg.empty());
 }

 TEST_F(MemMapTest, RemapAtEnd) {
   RemapAtEndTest(false);
 }

 #ifdef __LP64__
 TEST_F(MemMapTest, RemapAtEnd32bit) {
   RemapAtEndTest(true);
 }
 #endif

 TEST_F(MemMapTest, MapAnonymousExactAddr32bitHighAddr) {
   CommonInit();
   // This test may not work under valgrind.
   if (RUNNING_ON_VALGRIND == 0) {
     uintptr_t start_addr = ART_BASE_ADDRESS + 0x1000000;
     std::string error_msg;
     std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousExactAddr32bitHighAddr",
                                                      reinterpret_cast<uint8_t*>(start_addr),
                                                      0x21000000,
                                                      PROT_READ | PROT_WRITE,
                                                      true,
                                                      false,
                                                      &error_msg));
     ASSERT_TRUE(map.get() != nullptr) << error_msg;
     ASSERT_TRUE(error_msg.empty());
     ASSERT_EQ(reinterpret_cast<uintptr_t>(BaseBegin(map.get())), start_addr);
   }
 }

 TEST_F(MemMapTest, MapAnonymousOverflow) {
   CommonInit();
   std::string error_msg;
   uintptr_t ptr = 0;
   ptr -= kPageSize;  // Now it's close to the top.
   std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousOverflow",
                                                    reinterpret_cast<uint8_t*>(ptr),
                                                    2 * kPageSize,  // brings it over the top.
                                                    PROT_READ | PROT_WRITE,
                                                    false,
                                                    false,
                                                    &error_msg));
   ASSERT_EQ(nullptr, map.get());
   ASSERT_FALSE(error_msg.empty());
 }

 #ifdef __LP64__
 TEST_F(MemMapTest, MapAnonymousLow4GBExpectedTooHigh) {
   CommonInit();
   std::string error_msg;
   std::unique_ptr<MemMap> map(
       MemMap::MapAnonymous("MapAnonymousLow4GBExpectedTooHigh",
                            reinterpret_cast<uint8_t*>(UINT64_C(0x100000000)),
                            kPageSize,
                            PROT_READ | PROT_WRITE,
                            true,
                            false,
                            &error_msg));
   ASSERT_EQ(nullptr, map.get());
   ASSERT_FALSE(error_msg.empty());
 }

 TEST_F(MemMapTest, MapAnonymousLow4GBRangeTooHigh) {
   CommonInit();
   std::string error_msg;
   std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousLow4GBRangeTooHigh",
                                                    reinterpret_cast<uint8_t*>(0xF0000000),
                                                    0x20000000,
                                                    PROT_READ | PROT_WRITE,
                                                    true,
                                                    false,
                                                    &error_msg));
   ASSERT_EQ(nullptr, map.get());
   ASSERT_FALSE(error_msg.empty());
 }
 #endif

 TEST_F(MemMapTest, MapAnonymousReuse) {
   CommonInit();
   std::string error_msg;
   std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousReserve",
                                                    nullptr,
                                                    0x20000,
                                                    PROT_READ | PROT_WRITE,
                                                    false,
                                                    false,
                                                    &error_msg));
   ASSERT_NE(nullptr, map.get());
   ASSERT_TRUE(error_msg.empty());
   std::unique_ptr<MemMap> map2(MemMap::MapAnonymous("MapAnonymousReused",
                                                     reinterpret_cast<uint8_t*>(map->BaseBegin()),
                                                     0x10000,
                                                     PROT_READ | PROT_WRITE,
                                                     false,
                                                     true,
                                                     &error_msg));
   ASSERT_NE(nullptr, map2.get());
   ASSERT_TRUE(error_msg.empty());
 }

 TEST_F(MemMapTest, CheckNoGaps) {
   CommonInit();
   std::string error_msg;
   constexpr size_t kNumPages = 3;
   // Map a 3-page mem map.
   std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymous0",
                                                    nullptr,
                                                    kPageSize * kNumPages,
                                                    PROT_READ | PROT_WRITE,
                                                    false,
                                                    false,
                                                    &error_msg));
   ASSERT_TRUE(map.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());
   // Record the base address.
   uint8_t* map_base = reinterpret_cast<uint8_t*>(map->BaseBegin());
   // Unmap it.
   map.reset();

   // Map at the same address, but in page-sized separate mem maps,
   // assuming the space at the address is still available.
   std::unique_ptr<MemMap> map0(MemMap::MapAnonymous("MapAnonymous0",
                                                     map_base,
                                                     kPageSize,
                                                     PROT_READ | PROT_WRITE,
                                                     false,
                                                     false,
                                                     &error_msg));
   ASSERT_TRUE(map0.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());
   std::unique_ptr<MemMap> map1(MemMap::MapAnonymous("MapAnonymous1",
                                                     map_base + kPageSize,
                                                     kPageSize,
                                                     PROT_READ | PROT_WRITE,
                                                     false,
                                                     false,
                                                     &error_msg));
   ASSERT_TRUE(map1.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());
   std::unique_ptr<MemMap> map2(MemMap::MapAnonymous("MapAnonymous2",
                                                     map_base + kPageSize * 2,
                                                     kPageSize,
                                                     PROT_READ | PROT_WRITE,
                                                     false,
                                                     false,
                                                     &error_msg));
   ASSERT_TRUE(map2.get() != nullptr) << error_msg;
   ASSERT_TRUE(error_msg.empty());

   // One-map cases.
   ASSERT_TRUE(MemMap::CheckNoGaps(map0.get(), map0.get()));
   ASSERT_TRUE(MemMap::CheckNoGaps(map1.get(), map1.get()));
   ASSERT_TRUE(MemMap::CheckNoGaps(map2.get(), map2.get()));

   // Two or three-map cases.
   ASSERT_TRUE(MemMap::CheckNoGaps(map0.get(), map1.get()));
   ASSERT_TRUE(MemMap::CheckNoGaps(map1.get(), map2.get()));
   ASSERT_TRUE(MemMap::CheckNoGaps(map0.get(), map2.get()));

   // Unmap the middle one.
   map1.reset();

   // Should return false now that there's a gap in the middle.
   ASSERT_FALSE(MemMap::CheckNoGaps(map0.get(), map2.get()));
 }

 }  // namespace art
	/*
	* Copyright (C) 2013 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "mem_map.h"

	#include <memory>

	#include <valgrind.h>

	#include "gtest/gtest.h"

	namespace art {

	class MemMapTest : public testing::Test {
	public:
	static uint8_t* BaseBegin(MemMap* mem_map) {
	return reinterpret_cast<uint8_t*>(mem_map->base_begin_);
	}
	static size_t BaseSize(MemMap* mem_map) {
	return mem_map->base_size_;
	}

	static void RemapAtEndTest(bool low_4gb) {
	std::string error_msg;
	// Cast the page size to size_t.
	const size_t page_size = static_cast<size_t>(kPageSize);
	// Map a two-page memory region.
	MemMap* m0 = MemMap::MapAnonymous("MemMapTest_RemapAtEndTest_map0",
	nullptr,
	2 * page_size,
	PROT_READ \| PROT_WRITE,
	low_4gb,
	false,
	&error_msg);
	// Check its state and write to it.
	uint8_t* base0 = m0->Begin();
	ASSERT_TRUE(base0 != nullptr) << error_msg;
	size_t size0 = m0->Size();
	EXPECT_EQ(m0->Size(), 2 * page_size);
	EXPECT_EQ(BaseBegin(m0), base0);
	EXPECT_EQ(BaseSize(m0), size0);
	memset(base0, 42, 2 * page_size);
	// Remap the latter half into a second MemMap.
	MemMap* m1 = m0->RemapAtEnd(base0 + page_size,
	"MemMapTest_RemapAtEndTest_map1",
	PROT_READ \| PROT_WRITE,
	&error_msg);
	// Check the states of the two maps.
	EXPECT_EQ(m0->Begin(), base0) << error_msg;
	EXPECT_EQ(m0->Size(), page_size);
	EXPECT_EQ(BaseBegin(m0), base0);
	EXPECT_EQ(BaseSize(m0), page_size);
	uint8_t* base1 = m1->Begin();
	size_t size1 = m1->Size();
	EXPECT_EQ(base1, base0 + page_size);
	EXPECT_EQ(size1, page_size);
	EXPECT_EQ(BaseBegin(m1), base1);
	EXPECT_EQ(BaseSize(m1), size1);
	// Write to the second region.
	memset(base1, 43, page_size);
	// Check the contents of the two regions.
	for (size_t i = 0; i < page_size; ++i) {
	EXPECT_EQ(base0[i], 42);
	}
	for (size_t i = 0; i < page_size; ++i) {
	EXPECT_EQ(base1[i], 43);
	}
	// Unmap the first region.
	delete m0;
	// Make sure the second region is still accessible after the first
	// region is unmapped.
	for (size_t i = 0; i < page_size; ++i) {
	EXPECT_EQ(base1[i], 43);
	}
	delete m1;
	}

	void CommonInit() {
	MemMap::Init();
	}

	#if defined(__LP64__) && !defined(__x86_64__)
	static uintptr_t GetLinearScanPos() {
	return MemMap::next_mem_pos_;
	}
	#endif
	};

	#if defined(__LP64__) && !defined(__x86_64__)

	#ifdef __BIONIC__
	extern uintptr_t CreateStartPos(uint64_t input);
	#endif

	TEST_F(MemMapTest, Start) {
	CommonInit();
	uintptr_t start = GetLinearScanPos();
	EXPECT_LE(64 * KB, start);
	EXPECT_LT(start, static_cast<uintptr_t>(ART_BASE_ADDRESS));
	#ifdef __BIONIC__
	// Test a couple of values. Make sure they are different.
	uintptr_t last = 0;
	for (size_t i = 0; i < 100; ++i) {
	uintptr_t random_start = CreateStartPos(i * kPageSize);
	EXPECT_NE(last, random_start);
	last = random_start;
	}

	// Even on max, should be below ART_BASE_ADDRESS.
	EXPECT_LT(CreateStartPos(~0), static_cast<uintptr_t>(ART_BASE_ADDRESS));
	#endif
	// End of test.
	}
	#endif

	TEST_F(MemMapTest, MapAnonymousEmpty) {
	CommonInit();
	std::string error_msg;
	std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousEmpty",
	nullptr,
	0,
	PROT_READ,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	map.reset(MemMap::MapAnonymous("MapAnonymousEmpty",
	nullptr,
	kPageSize,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	}

	#ifdef __LP64__
	TEST_F(MemMapTest, MapAnonymousEmpty32bit) {
	CommonInit();
	std::string error_msg;
	std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousEmpty",
	nullptr,
	kPageSize,
	PROT_READ \| PROT_WRITE,
	true,
	false,
	&error_msg));
	ASSERT_TRUE(map.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	ASSERT_LT(reinterpret_cast<uintptr_t>(BaseBegin(map.get())), 1ULL << 32);
	}
	#endif

	TEST_F(MemMapTest, MapAnonymousExactAddr) {
	CommonInit();
	std::string error_msg;
	// Map at an address that should work, which should succeed.
	std::unique_ptr<MemMap> map0(MemMap::MapAnonymous("MapAnonymous0",
	reinterpret_cast<uint8_t*>(ART_BASE_ADDRESS),
	kPageSize,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map0.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	ASSERT_TRUE(map0->BaseBegin() == reinterpret_cast<void*>(ART_BASE_ADDRESS));
	// Map at an unspecified address, which should succeed.
	std::unique_ptr<MemMap> map1(MemMap::MapAnonymous("MapAnonymous1",
	nullptr,
	kPageSize,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map1.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	ASSERT_TRUE(map1->BaseBegin() != nullptr);
	// Attempt to map at the same address, which should fail.
	std::unique_ptr<MemMap> map2(MemMap::MapAnonymous("MapAnonymous2",
	reinterpret_cast<uint8_t*>(map1->BaseBegin()),
	kPageSize,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map2.get() == nullptr) << error_msg;
	ASSERT_TRUE(!error_msg.empty());
	}

	TEST_F(MemMapTest, RemapAtEnd) {
	RemapAtEndTest(false);
	}

	#ifdef __LP64__
	TEST_F(MemMapTest, RemapAtEnd32bit) {
	RemapAtEndTest(true);
	}
	#endif

	TEST_F(MemMapTest, MapAnonymousExactAddr32bitHighAddr) {
	CommonInit();
	// This test may not work under valgrind.
	if (RUNNING_ON_VALGRIND == 0) {
	uintptr_t start_addr = ART_BASE_ADDRESS + 0x1000000;
	std::string error_msg;
	std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousExactAddr32bitHighAddr",
	reinterpret_cast<uint8_t*>(start_addr),
	0x21000000,
	PROT_READ \| PROT_WRITE,
	true,
	false,
	&error_msg));
	ASSERT_TRUE(map.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	ASSERT_EQ(reinterpret_cast<uintptr_t>(BaseBegin(map.get())), start_addr);
	}
	}

	TEST_F(MemMapTest, MapAnonymousOverflow) {
	CommonInit();
	std::string error_msg;
	uintptr_t ptr = 0;
	ptr -= kPageSize; // Now it's close to the top.
	std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousOverflow",
	reinterpret_cast<uint8_t*>(ptr),
	2 * kPageSize, // brings it over the top.
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_EQ(nullptr, map.get());
	ASSERT_FALSE(error_msg.empty());
	}

	#ifdef __LP64__
	TEST_F(MemMapTest, MapAnonymousLow4GBExpectedTooHigh) {
	CommonInit();
	std::string error_msg;
	std::unique_ptr<MemMap> map(
	MemMap::MapAnonymous("MapAnonymousLow4GBExpectedTooHigh",
	reinterpret_cast<uint8_t*>(UINT64_C(0x100000000)),
	kPageSize,
	PROT_READ \| PROT_WRITE,
	true,
	false,
	&error_msg));
	ASSERT_EQ(nullptr, map.get());
	ASSERT_FALSE(error_msg.empty());
	}

	TEST_F(MemMapTest, MapAnonymousLow4GBRangeTooHigh) {
	CommonInit();
	std::string error_msg;
	std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousLow4GBRangeTooHigh",
	reinterpret_cast<uint8_t*>(0xF0000000),
	0x20000000,
	PROT_READ \| PROT_WRITE,
	true,
	false,
	&error_msg));
	ASSERT_EQ(nullptr, map.get());
	ASSERT_FALSE(error_msg.empty());
	}
	#endif

	TEST_F(MemMapTest, MapAnonymousReuse) {
	CommonInit();
	std::string error_msg;
	std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymousReserve",
	nullptr,
	0x20000,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_NE(nullptr, map.get());
	ASSERT_TRUE(error_msg.empty());
	std::unique_ptr<MemMap> map2(MemMap::MapAnonymous("MapAnonymousReused",
	reinterpret_cast<uint8_t*>(map->BaseBegin()),
	0x10000,
	PROT_READ \| PROT_WRITE,
	false,
	true,
	&error_msg));
	ASSERT_NE(nullptr, map2.get());
	ASSERT_TRUE(error_msg.empty());
	}

	TEST_F(MemMapTest, CheckNoGaps) {
	CommonInit();
	std::string error_msg;
	constexpr size_t kNumPages = 3;
	// Map a 3-page mem map.
	std::unique_ptr<MemMap> map(MemMap::MapAnonymous("MapAnonymous0",
	nullptr,
	kPageSize * kNumPages,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	// Record the base address.
	uint8_t* map_base = reinterpret_cast<uint8_t*>(map->BaseBegin());
	// Unmap it.
	map.reset();

	// Map at the same address, but in page-sized separate mem maps,
	// assuming the space at the address is still available.
	std::unique_ptr<MemMap> map0(MemMap::MapAnonymous("MapAnonymous0",
	map_base,
	kPageSize,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map0.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	std::unique_ptr<MemMap> map1(MemMap::MapAnonymous("MapAnonymous1",
	map_base + kPageSize,
	kPageSize,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map1.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());
	std::unique_ptr<MemMap> map2(MemMap::MapAnonymous("MapAnonymous2",
	map_base + kPageSize * 2,
	kPageSize,
	PROT_READ \| PROT_WRITE,
	false,
	false,
	&error_msg));
	ASSERT_TRUE(map2.get() != nullptr) << error_msg;
	ASSERT_TRUE(error_msg.empty());

	// One-map cases.
	ASSERT_TRUE(MemMap::CheckNoGaps(map0.get(), map0.get()));
	ASSERT_TRUE(MemMap::CheckNoGaps(map1.get(), map1.get()));
	ASSERT_TRUE(MemMap::CheckNoGaps(map2.get(), map2.get()));

	// Two or three-map cases.
	ASSERT_TRUE(MemMap::CheckNoGaps(map0.get(), map1.get()));
	ASSERT_TRUE(MemMap::CheckNoGaps(map1.get(), map2.get()));
	ASSERT_TRUE(MemMap::CheckNoGaps(map0.get(), map2.get()));

	// Unmap the middle one.
	map1.reset();

	// Should return false now that there's a gap in the middle.
	ASSERT_FALSE(MemMap::CheckNoGaps(map0.get(), map2.get()));
	}

	} // namespace art