Properly handle empty map after read-only map.

Recently, the maps for an elf in memory might show up looking like:

  f0000-f1000 0 r-- /system/lib/libc.so
  f1000-f2000 0 ---
  f2000-f3000 1000 r-x /system/lib/libc.so
  f3000-f4000 2000 rw- /system/lib/libc.so

The problem is that there is logic in the code that assumed that the
map before the execute map must be the read-only map. In the case
above, this is not true. Add a new prev_real_map that will point
to the previous map that is not one of these empty maps.

This will fix the backtraces that look like this:

  #00  pc 0000000000050d58  /apex/com.android.runtime/lib64/bionic/libc.so!libc.so (offset 0x50000) (syscall+24) (BuildId: 5252408bf30e395d49ee270b54c77ca4)

To get rid of the !libc.so and the offset value, which is not correct.

Added new unit tests to verify this.
Added new offline test which an empty map between read-only and execute
map. Before this change, the backtraces had lines like
libc.so!libc.so (offset XXX) would be present.

Bug: 148075852

Test: Ran unit tests.
Change-Id: Ie04bfc96b8f91ed885cb1e655cf1e346efe48a45

17 files changed, 170 insertions, 69 deletions

diff --git a/libunwindstack/tests/DexFileTest.cpp b/libunwindstack/tests/DexFileTest.cpp
index 0149a42..1b54da6 100644
--- a/libunwindstack/tests/DexFileTest.cpp
+++ b/libunwindstack/tests/DexFileTest.cpp
@@ -105,7 +105,7 @@ TEST(DexFileTest, create_using_file) {
             static_cast<size_t>(TEMP_FAILURE_RETRY(write(tf.fd, kDexData, sizeof(kDexData)))));
 
   MemoryFake memory;
-  MapInfo info(nullptr, 0, 0x10000, 0, 0x5, tf.path);
+  MapInfo info(nullptr, nullptr, 0, 0x10000, 0, 0x5, tf.path);
   EXPECT_TRUE(DexFile::Create(0x500, &memory, &info) != nullptr);
 }
 
@@ -118,7 +118,7 @@ TEST(DexFileTest, create_using_file_non_zero_start) {
             static_cast<size_t>(TEMP_FAILURE_RETRY(write(tf.fd, kDexData, sizeof(kDexData)))));
 
   MemoryFake memory;
-  MapInfo info(nullptr, 0x100, 0x10000, 0, 0x5, tf.path);
+  MapInfo info(nullptr, nullptr, 0x100, 0x10000, 0, 0x5, tf.path);
   EXPECT_TRUE(DexFile::Create(0x600, &memory, &info) != nullptr);
 }
 
@@ -131,21 +131,21 @@ TEST(DexFileTest, create_using_file_non_zero_offset) {
             static_cast<size_t>(TEMP_FAILURE_RETRY(write(tf.fd, kDexData, sizeof(kDexData)))));
 
   MemoryFake memory;
-  MapInfo info(nullptr, 0x100, 0x10000, 0x200, 0x5, tf.path);
+  MapInfo info(nullptr, nullptr, 0x100, 0x10000, 0x200, 0x5, tf.path);
   EXPECT_TRUE(DexFile::Create(0x400, &memory, &info) != nullptr);
 }
 
 TEST(DexFileTest, create_using_memory_empty_file) {
   MemoryFake memory;
   memory.SetMemory(0x4000, kDexData, sizeof(kDexData));
-  MapInfo info(nullptr, 0x100, 0x10000, 0x200, 0x5, "");
+  MapInfo info(nullptr, nullptr, 0x100, 0x10000, 0x200, 0x5, "");
   EXPECT_TRUE(DexFile::Create(0x4000, &memory, &info) != nullptr);
 }
 
 TEST(DexFileTest, create_using_memory_file_does_not_exist) {
   MemoryFake memory;
   memory.SetMemory(0x4000, kDexData, sizeof(kDexData));
-  MapInfo info(nullptr, 0x100, 0x10000, 0x200, 0x5, "/does/not/exist");
+  MapInfo info(nullptr, nullptr, 0x100, 0x10000, 0x200, 0x5, "/does/not/exist");
   EXPECT_TRUE(DexFile::Create(0x4000, &memory, &info) != nullptr);
 }
 
@@ -158,7 +158,7 @@ TEST(DexFileTest, create_using_memory_file_is_malformed) {
 
   MemoryFake memory;
   memory.SetMemory(0x4000, kDexData, sizeof(kDexData));
-  MapInfo info(nullptr, 0x4000, 0x10000, 0x200, 0x5, "/does/not/exist");
+  MapInfo info(nullptr, nullptr, 0x4000, 0x10000, 0x200, 0x5, "/does/not/exist");
   std::unique_ptr<DexFile> dex_file = DexFile::Create(0x4000, &memory, &info);
   ASSERT_TRUE(dex_file != nullptr);
 
@@ -171,7 +171,7 @@ TEST(DexFileTest, create_using_memory_file_is_malformed) {
 TEST(DexFileTest, get_method) {
   MemoryFake memory;
   memory.SetMemory(0x4000, kDexData, sizeof(kDexData));
-  MapInfo info(nullptr, 0x100, 0x10000, 0x200, 0x5, "");
+  MapInfo info(nullptr, nullptr, 0x100, 0x10000, 0x200, 0x5, "");
   std::unique_ptr<DexFile> dex_file(DexFile::Create(0x4000, &memory, &info));
   ASSERT_TRUE(dex_file != nullptr);
 
@@ -189,7 +189,7 @@ TEST(DexFileTest, get_method) {
 TEST(DexFileTest, get_method_empty) {
   MemoryFake memory;
   memory.SetMemory(0x4000, kDexData, sizeof(kDexData));
-  MapInfo info(nullptr, 0x100, 0x10000, 0x200, 0x5, "");
+  MapInfo info(nullptr, nullptr, 0x100, 0x10000, 0x200, 0x5, "");
   std::unique_ptr<DexFile> dex_file(DexFile::Create(0x4000, &memory, &info));
   ASSERT_TRUE(dex_file != nullptr);
 
diff --git a/libunwindstack/tests/ElfCacheTest.cpp b/libunwindstack/tests/ElfCacheTest.cpp
index 5735858..5f13546 100644
--- a/libunwindstack/tests/ElfCacheTest.cpp
+++ b/libunwindstack/tests/ElfCacheTest.cpp
@@ -78,8 +78,8 @@ void ElfCacheTest::VerifySameMap(bool cache_enabled) {
 
   uint64_t start = 0x1000;
   uint64_t end = 0x20000;
-  MapInfo info1(nullptr, start, end, 0, 0x5, tf.path);
-  MapInfo info2(nullptr, start, end, 0, 0x5, tf.path);
+  MapInfo info1(nullptr, nullptr, start, end, 0, 0x5, tf.path);
+  MapInfo info2(nullptr, nullptr, start, end, 0, 0x5, tf.path);
 
   Elf* elf1 = info1.GetElf(memory_, ARCH_ARM);
   ASSERT_TRUE(elf1->valid());
@@ -119,17 +119,17 @@ void ElfCacheTest::VerifyWithinSameMap(bool cache_enabled) {
   uint64_t start = 0x1000;
   uint64_t end = 0x20000;
   // Will have an elf at offset 0 in file.
-  MapInfo info0_1(nullptr, start, end, 0, 0x5, tf.path);
-  MapInfo info0_2(nullptr, start, end, 0, 0x5, tf.path);
+  MapInfo info0_1(nullptr, nullptr, start, end, 0, 0x5, tf.path);
+  MapInfo info0_2(nullptr, nullptr, start, end, 0, 0x5, tf.path);
   // Will have an elf at offset 0x100 in file.
-  MapInfo info100_1(nullptr, start, end, 0x100, 0x5, tf.path);
-  MapInfo info100_2(nullptr, start, end, 0x100, 0x5, tf.path);
+  MapInfo info100_1(nullptr, nullptr, start, end, 0x100, 0x5, tf.path);
+  MapInfo info100_2(nullptr, nullptr, start, end, 0x100, 0x5, tf.path);
   // Will have an elf at offset 0x200 in file.
-  MapInfo info200_1(nullptr, start, end, 0x200, 0x5, tf.path);
-  MapInfo info200_2(nullptr, start, end, 0x200, 0x5, tf.path);
+  MapInfo info200_1(nullptr, nullptr, start, end, 0x200, 0x5, tf.path);
+  MapInfo info200_2(nullptr, nullptr, start, end, 0x200, 0x5, tf.path);
   // Will have an elf at offset 0 in file.
-  MapInfo info300_1(nullptr, start, end, 0x300, 0x5, tf.path);
-  MapInfo info300_2(nullptr, start, end, 0x300, 0x5, tf.path);
+  MapInfo info300_1(nullptr, nullptr, start, end, 0x300, 0x5, tf.path);
+  MapInfo info300_2(nullptr, nullptr, start, end, 0x300, 0x5, tf.path);
 
   Elf* elf0_1 = info0_1.GetElf(memory_, ARCH_ARM);
   ASSERT_TRUE(elf0_1->valid());
@@ -216,10 +216,10 @@ void ElfCacheTest::VerifyWithinSameMapNeverReadAtZero(bool cache_enabled) {
   uint64_t start = 0x1000;
   uint64_t end = 0x20000;
   // Multiple info sections at different offsets will have non-zero elf offsets.
-  MapInfo info300_1(nullptr, start, end, 0x300, 0x5, tf.path);
-  MapInfo info300_2(nullptr, start, end, 0x300, 0x5, tf.path);
-  MapInfo info400_1(nullptr, start, end, 0x400, 0x5, tf.path);
-  MapInfo info400_2(nullptr, start, end, 0x400, 0x5, tf.path);
+  MapInfo info300_1(nullptr, nullptr, start, end, 0x300, 0x5, tf.path);
+  MapInfo info300_2(nullptr, nullptr, start, end, 0x300, 0x5, tf.path);
+  MapInfo info400_1(nullptr, nullptr, start, end, 0x400, 0x5, tf.path);
+  MapInfo info400_2(nullptr, nullptr, start, end, 0x400, 0x5, tf.path);
 
   Elf* elf300_1 = info300_1.GetElf(memory_, ARCH_ARM);
   ASSERT_TRUE(elf300_1->valid());
diff --git a/libunwindstack/tests/ElfTest.cpp b/libunwindstack/tests/ElfTest.cpp
index 4866345..1f3ed81 100644
--- a/libunwindstack/tests/ElfTest.cpp
+++ b/libunwindstack/tests/ElfTest.cpp
@@ -275,7 +275,7 @@ TEST_F(ElfTest, rel_pc) {
   elf.FakeSetInterface(interface);
 
   elf.FakeSetValid(true);
-  MapInfo map_info(nullptr, 0x1000, 0x2000, 0, 0, "");
+  MapInfo map_info(nullptr, nullptr, 0x1000, 0x2000, 0, 0, "");
 
   ASSERT_EQ(0x101U, elf.GetRelPc(0x1101, &map_info));
 
diff --git a/libunwindstack/tests/MapInfoCreateMemoryTest.cpp b/libunwindstack/tests/MapInfoCreateMemoryTest.cpp
index 6c1cfa2..6d8d58e 100644
--- a/libunwindstack/tests/MapInfoCreateMemoryTest.cpp
+++ b/libunwindstack/tests/MapInfoCreateMemoryTest.cpp
@@ -89,7 +89,7 @@ class MapInfoCreateMemoryTest : public ::testing::Test {
 };
 
 TEST_F(MapInfoCreateMemoryTest, end_le_start) {
-  MapInfo info(nullptr, 0x100, 0x100, 0, 0, elf_.path);
+  MapInfo info(nullptr, nullptr, 0x100, 0x100, 0, 0, elf_.path);
 
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() == nullptr);
@@ -108,7 +108,7 @@ TEST_F(MapInfoCreateMemoryTest, end_le_start) {
 // Verify that if the offset is non-zero but there is no elf at the offset,
 // that the full file is used.
 TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_full_file) {
-  MapInfo info(nullptr, 0x100, 0x200, 0x100, 0, elf_.path);
+  MapInfo info(nullptr, nullptr, 0x100, 0x200, 0x100, 0, elf_.path);
 
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() != nullptr);
@@ -129,8 +129,9 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_full_file) {
 
   // Now verify the elf start offset is set correctly based on the previous
   // info.
-  MapInfo prev_info(nullptr, 0, 0x100, 0x10, 0, "");
+  MapInfo prev_info(nullptr, nullptr, 0, 0x100, 0x10, 0, "");
   info.prev_map = &prev_info;
+  info.prev_real_map = &prev_info;
 
   // No preconditions met, change each one until it should set the elf start
   // offset to zero.
@@ -177,7 +178,7 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_full_file) {
 // Verify that if the offset is non-zero and there is an elf at that
 // offset, that only part of the file is used.
 TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_partial_file) {
-  MapInfo info(nullptr, 0x100, 0x200, 0x1000, 0, elf_at_1000_.path);
+  MapInfo info(nullptr, nullptr, 0x100, 0x200, 0x1000, 0, elf_at_1000_.path);
 
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() != nullptr);
@@ -202,7 +203,7 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_partial_file) {
 // embedded elf is bigger than the initial map, the new object is larger
 // than the original map size. Do this for a 32 bit elf and a 64 bit elf.
 TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_partial_file_whole_elf32) {
-  MapInfo info(nullptr, 0x5000, 0x6000, 0x1000, 0, elf32_at_map_.path);
+  MapInfo info(nullptr, nullptr, 0x5000, 0x6000, 0x1000, 0, elf32_at_map_.path);
 
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() != nullptr);
@@ -220,7 +221,7 @@ TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_partial_file_whole_e
 }
 
 TEST_F(MapInfoCreateMemoryTest, file_backed_non_zero_offset_partial_file_whole_elf64) {
-  MapInfo info(nullptr, 0x7000, 0x8000, 0x2000, 0, elf64_at_map_.path);
+  MapInfo info(nullptr, nullptr, 0x7000, 0x8000, 0x2000, 0, elf64_at_map_.path);
 
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() != nullptr);
@@ -243,14 +244,14 @@ TEST_F(MapInfoCreateMemoryTest, check_device_maps) {
   // be returned if the file mapping fails, but the device check is incorrect.
   std::vector<uint8_t> buffer(1024);
   uint64_t start = reinterpret_cast<uint64_t>(buffer.data());
-  MapInfo info(nullptr, start, start + buffer.size(), 0, 0x8000, "/dev/something");
+  MapInfo info(nullptr, nullptr, start, start + buffer.size(), 0, 0x8000, "/dev/something");
 
   std::unique_ptr<Memory> memory(info.CreateMemory(process_memory_));
   ASSERT_TRUE(memory.get() == nullptr);
 }
 
 TEST_F(MapInfoCreateMemoryTest, process_memory) {
-  MapInfo info(nullptr, 0x2000, 0x3000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x2000, 0x3000, 0, PROT_READ, "");
 
   Elf32_Ehdr ehdr = {};
   TestInitEhdr<Elf32_Ehdr>(&ehdr, ELFCLASS32, EM_ARM);
diff --git a/libunwindstack/tests/MapInfoGetBuildIDTest.cpp b/libunwindstack/tests/MapInfoGetBuildIDTest.cpp
index 16451d1..6953e26 100644
--- a/libunwindstack/tests/MapInfoGetBuildIDTest.cpp
+++ b/libunwindstack/tests/MapInfoGetBuildIDTest.cpp
@@ -50,7 +50,8 @@ class MapInfoGetBuildIDTest : public ::testing::Test {
     elf_interface_ = new ElfInterfaceFake(memory_);
     elf_->FakeSetInterface(elf_interface_);
     elf_container_.reset(elf_);
-    map_info_.reset(new MapInfo(nullptr, 0x1000, 0x20000, 0, PROT_READ | PROT_WRITE, tf_->path));
+    map_info_.reset(
+        new MapInfo(nullptr, nullptr, 0x1000, 0x20000, 0, PROT_READ | PROT_WRITE, tf_->path));
   }
 
   void MultipleThreadTest(std::string expected_build_id);
@@ -64,7 +65,7 @@ class MapInfoGetBuildIDTest : public ::testing::Test {
 };
 
 TEST_F(MapInfoGetBuildIDTest, no_elf_and_no_valid_elf_in_memory) {
-  MapInfo info(nullptr, 0x1000, 0x2000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x1000, 0x2000, 0, PROT_READ, "");
 
   EXPECT_EQ("", info.GetBuildID());
   EXPECT_EQ("", info.GetPrintableBuildID());
diff --git a/libunwindstack/tests/MapInfoGetElfTest.cpp b/libunwindstack/tests/MapInfoGetElfTest.cpp
index d60b8b1..7f97814 100644
--- a/libunwindstack/tests/MapInfoGetElfTest.cpp
+++ b/libunwindstack/tests/MapInfoGetElfTest.cpp
@@ -68,7 +68,7 @@ class MapInfoGetElfTest : public ::testing::Test {
 };
 
 TEST_F(MapInfoGetElfTest, invalid) {
-  MapInfo info(nullptr, 0x1000, 0x2000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x1000, 0x2000, 0, PROT_READ, "");
 
   // The map is empty, but this should still create an invalid elf object.
   Elf* elf = info.GetElf(process_memory_, ARCH_ARM);
@@ -77,7 +77,7 @@ TEST_F(MapInfoGetElfTest, invalid) {
 }
 
 TEST_F(MapInfoGetElfTest, valid32) {
-  MapInfo info(nullptr, 0x3000, 0x4000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x3000, 0x4000, 0, PROT_READ, "");
 
   Elf32_Ehdr ehdr;
   TestInitEhdr<Elf32_Ehdr>(&ehdr, ELFCLASS32, EM_ARM);
@@ -97,7 +97,7 @@ TEST_F(MapInfoGetElfTest, valid32) {
 }
 
 TEST_F(MapInfoGetElfTest, valid64) {
-  MapInfo info(nullptr, 0x8000, 0x9000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x8000, 0x9000, 0, PROT_READ, "");
 
   Elf64_Ehdr ehdr;
   TestInitEhdr<Elf64_Ehdr>(&ehdr, ELFCLASS64, EM_AARCH64);
@@ -111,7 +111,7 @@ TEST_F(MapInfoGetElfTest, valid64) {
 }
 
 TEST_F(MapInfoGetElfTest, invalid_arch_mismatch) {
-  MapInfo info(nullptr, 0x3000, 0x4000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x3000, 0x4000, 0, PROT_READ, "");
 
   Elf32_Ehdr ehdr;
   TestInitEhdr<Elf32_Ehdr>(&ehdr, ELFCLASS32, EM_ARM);
@@ -123,7 +123,7 @@ TEST_F(MapInfoGetElfTest, invalid_arch_mismatch) {
 }
 
 TEST_F(MapInfoGetElfTest, gnu_debugdata_init32) {
-  MapInfo info(nullptr, 0x2000, 0x3000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x2000, 0x3000, 0, PROT_READ, "");
 
   TestInitGnuDebugdata<Elf32_Ehdr, Elf32_Shdr>(ELFCLASS32, EM_ARM, true,
                                                [&](uint64_t offset, const void* ptr, size_t size) {
@@ -139,7 +139,7 @@ TEST_F(MapInfoGetElfTest, gnu_debugdata_init32) {
 }
 
 TEST_F(MapInfoGetElfTest, gnu_debugdata_init64) {
-  MapInfo info(nullptr, 0x5000, 0x8000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x5000, 0x8000, 0, PROT_READ, "");
 
   TestInitGnuDebugdata<Elf64_Ehdr, Elf64_Shdr>(ELFCLASS64, EM_AARCH64, true,
                                                [&](uint64_t offset, const void* ptr, size_t size) {
@@ -155,7 +155,7 @@ TEST_F(MapInfoGetElfTest, gnu_debugdata_init64) {
 }
 
 TEST_F(MapInfoGetElfTest, end_le_start) {
-  MapInfo info(nullptr, 0x1000, 0x1000, 0, PROT_READ, elf_.path);
+  MapInfo info(nullptr, nullptr, 0x1000, 0x1000, 0, PROT_READ, elf_.path);
 
   Elf32_Ehdr ehdr;
   TestInitEhdr<Elf32_Ehdr>(&ehdr, ELFCLASS32, EM_ARM);
@@ -182,7 +182,7 @@ TEST_F(MapInfoGetElfTest, end_le_start) {
 // Verify that if the offset is non-zero but there is no elf at the offset,
 // that the full file is used.
 TEST_F(MapInfoGetElfTest, file_backed_non_zero_offset_full_file) {
-  MapInfo info(nullptr, 0x1000, 0x2000, 0x100, PROT_READ, elf_.path);
+  MapInfo info(nullptr, nullptr, 0x1000, 0x2000, 0x100, PROT_READ, elf_.path);
 
   std::vector<uint8_t> buffer(0x1000);
   memset(buffer.data(), 0, buffer.size());
@@ -211,7 +211,7 @@ TEST_F(MapInfoGetElfTest, file_backed_non_zero_offset_full_file) {
 // Verify that if the offset is non-zero and there is an elf at that
 // offset, that only part of the file is used.
 TEST_F(MapInfoGetElfTest, file_backed_non_zero_offset_partial_file) {
-  MapInfo info(nullptr, 0x1000, 0x2000, 0x2000, PROT_READ, elf_.path);
+  MapInfo info(nullptr, nullptr, 0x1000, 0x2000, 0x2000, PROT_READ, elf_.path);
 
   std::vector<uint8_t> buffer(0x4000);
   memset(buffer.data(), 0, buffer.size());
@@ -241,7 +241,7 @@ TEST_F(MapInfoGetElfTest, file_backed_non_zero_offset_partial_file) {
 // embedded elf is bigger than the initial map, the new object is larger
 // than the original map size. Do this for a 32 bit elf and a 64 bit elf.
 TEST_F(MapInfoGetElfTest, file_backed_non_zero_offset_partial_file_whole_elf32) {
-  MapInfo info(nullptr, 0x5000, 0x6000, 0x1000, PROT_READ, elf_.path);
+  MapInfo info(nullptr, nullptr, 0x5000, 0x6000, 0x1000, PROT_READ, elf_.path);
 
   std::vector<uint8_t> buffer(0x4000);
   memset(buffer.data(), 0, buffer.size());
@@ -269,7 +269,7 @@ TEST_F(MapInfoGetElfTest, file_backed_non_zero_offset_partial_file_whole_elf32)
 }
 
 TEST_F(MapInfoGetElfTest, file_backed_non_zero_offset_partial_file_whole_elf64) {
-  MapInfo info(nullptr, 0x7000, 0x8000, 0x1000, PROT_READ, elf_.path);
+  MapInfo info(nullptr, nullptr, 0x7000, 0x8000, 0x1000, PROT_READ, elf_.path);
 
   std::vector<uint8_t> buffer(0x4000);
   memset(buffer.data(), 0, buffer.size());
@@ -297,7 +297,7 @@ TEST_F(MapInfoGetElfTest, file_backed_non_zero_offset_partial_file_whole_elf64)
 }
 
 TEST_F(MapInfoGetElfTest, check_device_maps) {
-  MapInfo info(nullptr, 0x7000, 0x8000, 0x1000, PROT_READ | MAPS_FLAGS_DEVICE_MAP,
+  MapInfo info(nullptr, nullptr, 0x7000, 0x8000, 0x1000, PROT_READ | MAPS_FLAGS_DEVICE_MAP,
                "/dev/something");
 
   // Create valid elf data in process memory for this to verify that only
@@ -343,7 +343,7 @@ TEST_F(MapInfoGetElfTest, multiple_thread_get_elf) {
   wait = true;
   // Create all of the threads and have them do the GetElf at the same time
   // to make it likely that a race will occur.
-  MapInfo info(nullptr, 0x7000, 0x8000, 0x1000, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x7000, 0x8000, 0x1000, PROT_READ, "");
   for (size_t i = 0; i < kNumConcurrentThreads; i++) {
     std::thread* thread = new std::thread([i, this, &wait, &info, &elf_in_threads]() {
       while (wait)
@@ -373,8 +373,8 @@ TEST_F(MapInfoGetElfTest, multiple_thread_get_elf) {
 
 // Verify that previous maps don't automatically get the same elf object.
 TEST_F(MapInfoGetElfTest, prev_map_elf_not_set) {
-  MapInfo info1(nullptr, 0x1000, 0x2000, 0, PROT_READ, "/not/present");
-  MapInfo info2(&info1, 0x2000, 0x3000, 0, PROT_READ, elf_.path);
+  MapInfo info1(nullptr, nullptr, 0x1000, 0x2000, 0, PROT_READ, "/not/present");
+  MapInfo info2(&info1, &info1, 0x2000, 0x3000, 0, PROT_READ, elf_.path);
 
   Elf32_Ehdr ehdr;
   TestInitEhdr<Elf32_Ehdr>(&ehdr, ELFCLASS32, EM_ARM);
@@ -389,8 +389,25 @@ TEST_F(MapInfoGetElfTest, prev_map_elf_not_set) {
 // Verify that a read-only map followed by a read-execute map will result
 // in the same elf object in both maps.
 TEST_F(MapInfoGetElfTest, read_only_followed_by_read_exec_share_elf) {
-  MapInfo r_info(nullptr, 0x1000, 0x2000, 0, PROT_READ, elf_.path);
-  MapInfo rw_info(&r_info, 0x2000, 0x3000, 0x1000, PROT_READ | PROT_EXEC, elf_.path);
+  MapInfo r_info(nullptr, nullptr, 0x1000, 0x2000, 0, PROT_READ, elf_.path);
+  MapInfo rw_info(&r_info, &r_info, 0x2000, 0x3000, 0x1000, PROT_READ | PROT_EXEC, elf_.path);
+
+  Elf32_Ehdr ehdr;
+  TestInitEhdr<Elf32_Ehdr>(&ehdr, ELFCLASS32, EM_ARM);
+  memory_->SetMemory(0x1000, &ehdr, sizeof(ehdr));
+  Elf* elf = rw_info.GetElf(process_memory_, ARCH_ARM);
+  ASSERT_TRUE(elf != nullptr);
+  ASSERT_TRUE(elf->valid());
+
+  ASSERT_EQ(elf, r_info.GetElf(process_memory_, ARCH_ARM));
+}
+
+// Verify that a read-only map followed by an empty map, then followed by
+// a read-execute map will result in the same elf object in both maps.
+TEST_F(MapInfoGetElfTest, read_only_followed_by_empty_then_read_exec_share_elf) {
+  MapInfo r_info(nullptr, nullptr, 0x1000, 0x2000, 0, PROT_READ, elf_.path);
+  MapInfo empty(&r_info, &r_info, 0x2000, 0x3000, 0, 0, "");
+  MapInfo rw_info(&empty, &r_info, 0x3000, 0x4000, 0x2000, PROT_READ | PROT_EXEC, elf_.path);
 
   Elf32_Ehdr ehdr;
   TestInitEhdr<Elf32_Ehdr>(&ehdr, ELFCLASS32, EM_ARM);
diff --git a/libunwindstack/tests/MapInfoGetLoadBiasTest.cpp b/libunwindstack/tests/MapInfoGetLoadBiasTest.cpp
index da3dbf2..971d452 100644
--- a/libunwindstack/tests/MapInfoGetLoadBiasTest.cpp
+++ b/libunwindstack/tests/MapInfoGetLoadBiasTest.cpp
@@ -50,7 +50,7 @@ class MapInfoGetLoadBiasTest : public ::testing::Test {
     process_memory_.reset(memory_);
     elf_ = new ElfFake(new MemoryFake);
     elf_container_.reset(elf_);
-    map_info_.reset(new MapInfo(nullptr, 0x1000, 0x20000, 0, PROT_READ | PROT_WRITE, ""));
+    map_info_.reset(new MapInfo(nullptr, nullptr, 0x1000, 0x20000, 0, PROT_READ | PROT_WRITE, ""));
   }
 
   void MultipleThreadTest(uint64_t expected_load_bias);
@@ -63,7 +63,7 @@ class MapInfoGetLoadBiasTest : public ::testing::Test {
 };
 
 TEST_F(MapInfoGetLoadBiasTest, no_elf_and_no_valid_elf_in_memory) {
-  MapInfo info(nullptr, 0x1000, 0x2000, 0, PROT_READ, "");
+  MapInfo info(nullptr, nullptr, 0x1000, 0x2000, 0, PROT_READ, "");
 
   EXPECT_EQ(0U, info.GetLoadBias(process_memory_));
 }
diff --git a/libunwindstack/tests/MapInfoTest.cpp b/libunwindstack/tests/MapInfoTest.cpp
index ef76b1b..98edc0e 100644
--- a/libunwindstack/tests/MapInfoTest.cpp
+++ b/libunwindstack/tests/MapInfoTest.cpp
@@ -26,8 +26,8 @@
 namespace unwindstack {
 
 TEST(MapInfoTest, maps_constructor_const_char) {
-  MapInfo prev_map(nullptr, 0, 0, 0, 0, "");
-  MapInfo map_info(&prev_map, 1, 2, 3, 4, "map");
+  MapInfo prev_map(nullptr, nullptr, 0, 0, 0, 0, "");
+  MapInfo map_info(&prev_map, &prev_map, 1, 2, 3, 4, "map");
 
   EXPECT_EQ(&prev_map, map_info.prev_map);
   EXPECT_EQ(1UL, map_info.start);
@@ -42,8 +42,8 @@ TEST(MapInfoTest, maps_constructor_const_char) {
 
 TEST(MapInfoTest, maps_constructor_string) {
   std::string name("string_map");
-  MapInfo prev_map(nullptr, 0, 0, 0, 0, "");
-  MapInfo map_info(&prev_map, 1, 2, 3, 4, name);
+  MapInfo prev_map(nullptr, nullptr, 0, 0, 0, 0, "");
+  MapInfo map_info(&prev_map, &prev_map, 1, 2, 3, 4, name);
 
   EXPECT_EQ(&prev_map, map_info.prev_map);
   EXPECT_EQ(1UL, map_info.start);
@@ -62,7 +62,7 @@ TEST(MapInfoTest, get_function_name) {
   elf->FakeSetInterface(interface);
   interface->FakePushFunctionData(FunctionData("function", 1000));
 
-  MapInfo map_info(nullptr, 1, 2, 3, 4, "");
+  MapInfo map_info(nullptr, nullptr, 1, 2, 3, 4, "");
   map_info.elf.reset(elf);
 
   std::string name;
diff --git a/libunwindstack/tests/MapsTest.cpp b/libunwindstack/tests/MapsTest.cpp
index 9e7a6ab..724eeb5 100644
--- a/libunwindstack/tests/MapsTest.cpp
+++ b/libunwindstack/tests/MapsTest.cpp
@@ -82,7 +82,7 @@ TEST(MapsTest, map_move) {
 }
 
 TEST(MapsTest, verify_parse_line) {
-  MapInfo info(nullptr, 0, 0, 0, 0, "");
+  MapInfo info(nullptr, nullptr, 0, 0, 0, 0, "");
 
   VerifyLine("01-02 rwxp 03 04:05 06\n", &info);
   EXPECT_EQ(1U, info.start);
@@ -155,7 +155,7 @@ TEST(MapsTest, verify_parse_line) {
 }
 
 TEST(MapsTest, verify_large_values) {
-  MapInfo info(nullptr, 0, 0, 0, 0, "");
+  MapInfo info(nullptr, nullptr, 0, 0, 0, 0, "");
 #if defined(__LP64__)
   VerifyLine("fabcdef012345678-f12345678abcdef8 rwxp f0b0d0f010305070 00:00 0\n", &info);
   EXPECT_EQ(0xfabcdef012345678UL, info.start);
diff --git a/libunwindstack/tests/RegsTest.cpp b/libunwindstack/tests/RegsTest.cpp
index 472d1cf..0a33e2f 100644
--- a/libunwindstack/tests/RegsTest.cpp
+++ b/libunwindstack/tests/RegsTest.cpp
@@ -182,7 +182,7 @@ TEST_F(RegsTest, elf_invalid) {
   RegsX86_64 regs_x86_64;
   RegsMips regs_mips;
   RegsMips64 regs_mips64;
-  MapInfo map_info(nullptr, 0x1000, 0x2000, 0, 0, "");
+  MapInfo map_info(nullptr, nullptr, 0x1000, 0x2000, 0, 0, "");
   Elf* invalid_elf = new Elf(nullptr);
   map_info.elf.reset(invalid_elf);
 
diff --git a/libunwindstack/tests/UnwindOfflineTest.cpp b/libunwindstack/tests/UnwindOfflineTest.cpp
index 364101a..c2bd836 100644
--- a/libunwindstack/tests/UnwindOfflineTest.cpp
+++ b/libunwindstack/tests/UnwindOfflineTest.cpp
@@ -169,15 +169,18 @@ std::unordered_map<std::string, uint32_t> UnwindOfflineTest::arm_regs_ = {
 };
 
 std::unordered_map<std::string, uint32_t> UnwindOfflineTest::arm64_regs_ = {
-    {"x0", ARM64_REG_R0},   {"x1", ARM64_REG_R1},   {"x2", ARM64_REG_R2},   {"x3", ARM64_REG_R3},
-    {"x4", ARM64_REG_R4},   {"x5", ARM64_REG_R5},   {"x6", ARM64_REG_R6},   {"x7", ARM64_REG_R7},
-    {"x8", ARM64_REG_R8},   {"x9", ARM64_REG_R9},   {"x10", ARM64_REG_R10}, {"x11", ARM64_REG_R11},
-    {"x12", ARM64_REG_R12}, {"x13", ARM64_REG_R13}, {"x14", ARM64_REG_R14}, {"x15", ARM64_REG_R15},
-    {"x16", ARM64_REG_R16}, {"x17", ARM64_REG_R17}, {"x18", ARM64_REG_R18}, {"x19", ARM64_REG_R19},
-    {"x20", ARM64_REG_R20}, {"x21", ARM64_REG_R21}, {"x22", ARM64_REG_R22}, {"x23", ARM64_REG_R23},
-    {"x24", ARM64_REG_R24}, {"x25", ARM64_REG_R25}, {"x26", ARM64_REG_R26}, {"x27", ARM64_REG_R27},
-    {"x28", ARM64_REG_R28}, {"x29", ARM64_REG_R29}, {"sp", ARM64_REG_SP},   {"lr", ARM64_REG_LR},
-    {"pc", ARM64_REG_PC},
+    {"x0", ARM64_REG_R0},      {"x1", ARM64_REG_R1},   {"x2", ARM64_REG_R2},
+    {"x3", ARM64_REG_R3},      {"x4", ARM64_REG_R4},   {"x5", ARM64_REG_R5},
+    {"x6", ARM64_REG_R6},      {"x7", ARM64_REG_R7},   {"x8", ARM64_REG_R8},
+    {"x9", ARM64_REG_R9},      {"x10", ARM64_REG_R10}, {"x11", ARM64_REG_R11},
+    {"x12", ARM64_REG_R12},    {"x13", ARM64_REG_R13}, {"x14", ARM64_REG_R14},
+    {"x15", ARM64_REG_R15},    {"x16", ARM64_REG_R16}, {"x17", ARM64_REG_R17},
+    {"x18", ARM64_REG_R18},    {"x19", ARM64_REG_R19}, {"x20", ARM64_REG_R20},
+    {"x21", ARM64_REG_R21},    {"x22", ARM64_REG_R22}, {"x23", ARM64_REG_R23},
+    {"x24", ARM64_REG_R24},    {"x25", ARM64_REG_R25}, {"x26", ARM64_REG_R26},
+    {"x27", ARM64_REG_R27},    {"x28", ARM64_REG_R28}, {"x29", ARM64_REG_R29},
+    {"sp", ARM64_REG_SP},      {"lr", ARM64_REG_LR},   {"pc", ARM64_REG_PC},
+    {"pst", ARM64_REG_PSTATE},
 };
 
 std::unordered_map<std::string, uint32_t> UnwindOfflineTest::x86_regs_ = {
@@ -1697,4 +1700,40 @@ TEST_F(UnwindOfflineTest, signal_load_bias_arm) {
   EXPECT_EQ(0xffe67d10ULL, unwinder.frames()[16].sp);
 }
 
+TEST_F(UnwindOfflineTest, empty_arm64) {
+  ASSERT_NO_FATAL_FAILURE(Init("empty_arm64/", ARCH_ARM64));
+
+  Unwinder unwinder(128, maps_.get(), regs_.get(), process_memory_);
+  unwinder.Unwind();
+
+  std::string frame_info(DumpFrames(unwinder));
+  ASSERT_EQ(7U, unwinder.NumFrames()) << "Unwind:\n" << frame_info;
+  EXPECT_EQ(
+      "  #00 pc 00000000000963a4  libc.so (__ioctl+4)\n"
+      "  #01 pc 000000000005344c  libc.so (ioctl+140)\n"
+      "  #02 pc 0000000000050ce4  libbinder.so "
+      "(android::IPCThreadState::talkWithDriver(bool)+308)\n"
+      "  #03 pc 0000000000050e98  libbinder.so "
+      "(android::IPCThreadState::getAndExecuteCommand()+24)\n"
+      "  #04 pc 00000000000516ac  libbinder.so (android::IPCThreadState::joinThreadPool(bool)+60)\n"
+      "  #05 pc 00000000000443b0  netd (main+1056)\n"
+      "  #06 pc 0000000000045594  libc.so (__libc_init+108)\n",
+      frame_info);
+
+  EXPECT_EQ(0x72a02203a4U, unwinder.frames()[0].pc);
+  EXPECT_EQ(0x7ffb6c0b50U, unwinder.frames()[0].sp);
+  EXPECT_EQ(0x72a01dd44cU, unwinder.frames()[1].pc);
+  EXPECT_EQ(0x7ffb6c0b50U, unwinder.frames()[1].sp);
+  EXPECT_EQ(0x729f759ce4U, unwinder.frames()[2].pc);
+  EXPECT_EQ(0x7ffb6c0c50U, unwinder.frames()[2].sp);
+  EXPECT_EQ(0x729f759e98U, unwinder.frames()[3].pc);
+  EXPECT_EQ(0x7ffb6c0ce0U, unwinder.frames()[3].sp);
+  EXPECT_EQ(0x729f75a6acU, unwinder.frames()[4].pc);
+  EXPECT_EQ(0x7ffb6c0d10U, unwinder.frames()[4].sp);
+  EXPECT_EQ(0x5d478af3b0U, unwinder.frames()[5].pc);
+  EXPECT_EQ(0x7ffb6c0d40U, unwinder.frames()[5].sp);
+  EXPECT_EQ(0x72a01cf594U, unwinder.frames()[6].pc);
+  EXPECT_EQ(0x7ffb6c0f30U, unwinder.frames()[6].sp);
+}
+
 }  // namespace unwindstack
diff --git a/libunwindstack/tests/files/offline/empty_arm64/libbinder.so b/libunwindstack/tests/files/offline/empty_arm64/libbinder.so
new file mode 100644
index 0000000..f30384c
--- /dev/null
+++ b/libunwindstack/tests/files/offline/empty_arm64/libbinder.so
diff --git a/libunwindstack/tests/files/offline/empty_arm64/libc.so b/libunwindstack/tests/files/offline/empty_arm64/libc.so
new file mode 100644
index 0000000..b05dcaf
--- /dev/null
+++ b/libunwindstack/tests/files/offline/empty_arm64/libc.so
diff --git a/libunwindstack/tests/files/offline/empty_arm64/maps.txt b/libunwindstack/tests/files/offline/empty_arm64/maps.txt
new file mode 100644
index 0000000..edb83c6
--- /dev/null
+++ b/libunwindstack/tests/files/offline/empty_arm64/maps.txt
@@ -0,0 +1,9 @@
+5d4786b000-5d47893000 r--p 0 00:00 0   netd
+5d47893000-5d47894000 ---p 0 00:00 0
+5d47894000-5d47901000 --xp 29000 00:00 0   netd
+729f709000-729f750000 r--p 0 00:00 0   libbinder.so
+729f750000-729f751000 ---p 0 00:00 0
+729f751000-729f794000 --xp 48000 00:00 0   libbinder.so
+72a018a000-72a01c2000 r--p 0 00:00 0   libc.so
+72a01c2000-72a01c3000 ---p 0 00:00 0
+72a01c3000-72a023b000 --xp 39000 00:00 0   libc.so
diff --git a/libunwindstack/tests/files/offline/empty_arm64/netd b/libunwindstack/tests/files/offline/empty_arm64/netd
new file mode 100644
index 0000000..8a72e94
--- /dev/null
+++ b/libunwindstack/tests/files/offline/empty_arm64/netd
diff --git a/libunwindstack/tests/files/offline/empty_arm64/regs.txt b/libunwindstack/tests/files/offline/empty_arm64/regs.txt
new file mode 100644
index 0000000..3d4279f
--- /dev/null
+++ b/libunwindstack/tests/files/offline/empty_arm64/regs.txt
@@ -0,0 +1,34 @@
+x0: 1d
+x1: c0306201
+x2: 7ffb6c0c50
+x3: 0
+x4: 0
+x5: 0
+x6: 0
+x7: 0
+x8: 1d
+x9: 7ffb6c0c00
+x10: 7ffb6c0c50
+x11: 7ffb6c0bd0
+x12: ffffff80ffffffd0
+x13: 0
+x14: 72a0240ce2
+x15: 20
+x16: 729f7a54e8
+x17: 72a01dd3c0
+x18: 72a0ac2000
+x19: 72a0666000
+x20: 719769b610
+x21: 719769b730
+x22: c0306201
+x23: fffffff7
+x24: 72a0666000
+x25: 0
+x26: 0
+x27: 0
+x28: 0
+x29: 7ffb6c0c30
+sp: 7ffb6c0b50
+lr: 72a01dd450
+pc: 72a02203a4
+pst: a0000000
diff --git a/libunwindstack/tests/files/offline/empty_arm64/stack.data b/libunwindstack/tests/files/offline/empty_arm64/stack.data
new file mode 100644
index 0000000..6d6108c
--- /dev/null
+++ b/libunwindstack/tests/files/offline/empty_arm64/stack.data