commit 0f40a0530976bc7fe2213944d69851821eb402c7
author Christopher Ferris <cferris@google.com> Wed Jan 22 12:17:06 2020 -0800
committer Christopher Ferris <cferris@google.com> Wed Jan 22 18:30:12 2020 -0800
tree 515b7c5168a6b3e58e5c73ebea9f0a7db38922e5
parent 929c9e8b40fe6adb23a140a8584d69edb2cab636

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

libunwindstack/tests/DexFileTest.cpp

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 @@
             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 @@
             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 @@
             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 @@
 
   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, 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_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);