Demand read load bias for a map.

Add a static GetLoadBias method to the Elf object that only reads just
enough to get the load bias.

Add a method to MapInfo that gets the load bias. First attempt to get
it if the elf object already exists. If no elf object was created, use
the new static method to get the load bias.

In BacktraceMap, add a custom iterator so that when code dereferences
a map element, that's when the load bias will be retrieved if it hasn't
already been set.

Bug: 69871050

Test: New unit tests, verify tombstones have non-zero load bias values for
Test: libraries with a non-zero load bias.
Change-Id: I125f4abc827589957fce2f0df24b0f25d037d732

14 files changed, 331 insertions, 23 deletions

diff --git a/libbacktrace/BacktraceMap.cpp b/libbacktrace/BacktraceMap.cpp
index 0e31495..0f1ae11 100644
--- a/libbacktrace/BacktraceMap.cpp
+++ b/libbacktrace/BacktraceMap.cpp
@@ -40,9 +40,10 @@ BacktraceMap::~BacktraceMap() {
 
 void BacktraceMap::FillIn(uintptr_t addr, backtrace_map_t* map) {
   ScopedBacktraceMapIteratorLock lock(this);
-  for (BacktraceMap::const_iterator it = begin(); it != end(); ++it) {
-    if (addr >= it->start && addr < it->end) {
-      *map = *it;
+  for (auto it = begin(); it != end(); ++it) {
+    const backtrace_map_t* entry = *it;
+    if (addr >= entry->start && addr < entry->end) {
+      *map = *entry;
       return;
     }
   }
diff --git a/libbacktrace/UnwindStackMap.cpp b/libbacktrace/UnwindStackMap.cpp
index 9ac0a0b..836a774 100644
--- a/libbacktrace/UnwindStackMap.cpp
+++ b/libbacktrace/UnwindStackMap.cpp
@@ -71,8 +71,19 @@ void UnwindStackMap::FillIn(uintptr_t addr, backtrace_map_t* map) {
   if (map_info == nullptr) {
     return;
   }
-  unwindstack::Elf* elf = map_info->GetElf(process_memory_, true);
-  map->load_bias = elf->GetLoadBias();
+  map->load_bias = map_info->GetLoadBias(process_memory_);
+}
+
+uint64_t UnwindStackMap::GetLoadBias(size_t index) {
+  if (index >= stack_maps_->Total()) {
+    return 0;
+  }
+
+  unwindstack::MapInfo* map_info = stack_maps_->Get(index);
+  if (map_info == nullptr) {
+    return 0;
+  }
+  return map_info->GetLoadBias(process_memory_);
 }
 
 std::string UnwindStackMap::GetFunctionName(uintptr_t pc, uintptr_t* offset) {
diff --git a/libbacktrace/UnwindStackMap.h b/libbacktrace/UnwindStackMap.h
index bc432e7..2f63655 100644
--- a/libbacktrace/UnwindStackMap.h
+++ b/libbacktrace/UnwindStackMap.h
@@ -42,6 +42,8 @@ class UnwindStackMap : public BacktraceMap {
   const std::shared_ptr<unwindstack::Memory>& process_memory() { return process_memory_; }
 
  protected:
+  uint64_t GetLoadBias(size_t index) override;
+
   std::unique_ptr<unwindstack::Maps> stack_maps_;
   std::shared_ptr<unwindstack::Memory> process_memory_;
 };
diff --git a/libbacktrace/backtrace_offline_test.cpp b/libbacktrace/backtrace_offline_test.cpp
index 0a1f33d..0935660 100644
--- a/libbacktrace/backtrace_offline_test.cpp
+++ b/libbacktrace/backtrace_offline_test.cpp
@@ -171,10 +171,12 @@ TEST(libbacktrace, DISABLED_generate_offline_testdata) {
   testdata += android::base::StringPrintf("pid: %d tid: %d\n", getpid(), arg.tid);
   // 2. Dump maps
   for (auto it = map->begin(); it != map->end(); ++it) {
-    testdata += android::base::StringPrintf(
-        "map: start: %" PRIxPTR " end: %" PRIxPTR " offset: %" PRIxPTR " load_bias: %" PRIxPTR
-        " flags: %d name: %s\n",
-        it->start, it->end, it->offset, it->load_bias, it->flags, it->name.c_str());
+    const backtrace_map_t* entry = *it;
+    testdata +=
+        android::base::StringPrintf("map: start: %" PRIxPTR " end: %" PRIxPTR " offset: %" PRIxPTR
+                                    " load_bias: %" PRIxPTR " flags: %d name: %s\n",
+                                    entry->start, entry->end, entry->offset, entry->load_bias,
+                                    entry->flags, entry->name.c_str());
   }
   // 3. Dump registers
   testdata += android::base::StringPrintf("registers: %zu ", sizeof(arg.unw_context));
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index 9911e74..890ab3f 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -857,6 +857,34 @@ struct map_test_t {
 
 static bool map_sort(map_test_t i, map_test_t j) { return i.start < j.start; }
 
+static std::string GetTestMapsAsString(const std::vector<map_test_t>& maps) {
+  if (maps.size() == 0) {
+    return "No test map entries\n";
+  }
+  std::string map_txt;
+  for (auto map : maps) {
+    map_txt += android::base::StringPrintf("%" PRIxPTR "-%" PRIxPTR "\n", map.start, map.end);
+  }
+  return map_txt;
+}
+
+static std::string GetMapsAsString(BacktraceMap* maps) {
+  if (maps->size() == 0) {
+    return "No map entries\n";
+  }
+  std::string map_txt;
+  for (const backtrace_map_t* map : *maps) {
+    map_txt += android::base::StringPrintf(
+        "%" PRIxPTR "-%" PRIxPTR " flags: 0x%x offset: 0x%" PRIxPTR " load_bias: 0x%" PRIxPTR,
+        map->start, map->end, map->flags, map->offset, map->load_bias);
+    if (!map->name.empty()) {
+      map_txt += ' ' + map->name;
+    }
+    map_txt += '\n';
+  }
+  return map_txt;
+}
+
 static void VerifyMap(pid_t pid) {
   char buffer[4096];
   snprintf(buffer, sizeof(buffer), "/proc/%d/maps", pid);
@@ -875,12 +903,20 @@ static void VerifyMap(pid_t pid) {
   std::unique_ptr<BacktraceMap> map(BacktraceMap::Create(pid));
 
   // Basic test that verifies that the map is in the expected order.
-  ScopedBacktraceMapIteratorLock lock(map.get());
-  std::vector<map_test_t>::const_iterator test_it = test_maps.begin();
-  for (BacktraceMap::const_iterator it = map->begin(); it != map->end(); ++it) {
-    ASSERT_TRUE(test_it != test_maps.end());
-    ASSERT_EQ(test_it->start, it->start);
-    ASSERT_EQ(test_it->end, it->end);
+  auto test_it = test_maps.begin();
+  for (auto it = map->begin(); it != map->end(); ++it) {
+    ASSERT_TRUE(test_it != test_maps.end()) << "Mismatch in number of maps, expected test maps:\n"
+                                            << GetTestMapsAsString(test_maps) << "Actual maps:\n"
+                                            << GetMapsAsString(map.get());
+    ASSERT_EQ(test_it->start, (*it)->start) << "Mismatch in map data, expected test maps:\n"
+                                            << GetTestMapsAsString(test_maps) << "Actual maps:\n"
+                                            << GetMapsAsString(map.get());
+    ASSERT_EQ(test_it->end, (*it)->end) << "Mismatch maps in map data, expected test maps:\n"
+                                        << GetTestMapsAsString(test_maps) << "Actual maps:\n"
+                                        << GetMapsAsString(map.get());
+    // Make sure the load bias get set to a value.
+    ASSERT_NE(static_cast<uint64_t>(-1), (*it)->load_bias) << "Found uninitialized load_bias\n"
+                                                           << GetMapsAsString(map.get());
     ++test_it;
   }
   ASSERT_TRUE(test_it == test_maps.end());
diff --git a/libbacktrace/include/backtrace/BacktraceMap.h b/libbacktrace/include/backtrace/BacktraceMap.h
index d078392..4ae68dd 100644
--- a/libbacktrace/include/backtrace/BacktraceMap.h
+++ b/libbacktrace/include/backtrace/BacktraceMap.h
@@ -30,6 +30,7 @@
 #endif
 
 #include <deque>
+#include <iterator>
 #include <string>
 #include <vector>
 
@@ -61,6 +62,49 @@ public:
 
   virtual ~BacktraceMap();
 
+  class iterator : public std::iterator<std::bidirectional_iterator_tag, backtrace_map_t*> {
+   public:
+    iterator(BacktraceMap* map, size_t index) : map_(map), index_(index) {}
+
+    iterator& operator++() {
+      index_++;
+      return *this;
+    }
+    iterator& operator++(int increment) {
+      index_ += increment;
+      return *this;
+    }
+    iterator& operator--() {
+      index_--;
+      return *this;
+    }
+    iterator& operator--(int decrement) {
+      index_ -= decrement;
+      return *this;
+    }
+
+    bool operator==(const iterator& rhs) { return this->index_ == rhs.index_; }
+    bool operator!=(const iterator& rhs) { return this->index_ != rhs.index_; }
+
+    const backtrace_map_t* operator*() {
+      if (index_ >= map_->size()) {
+        return nullptr;
+      }
+      backtrace_map_t* map = &map_->maps_[index_];
+      if (map->load_bias == static_cast<uintptr_t>(-1)) {
+        map->load_bias = map_->GetLoadBias(index_);
+      }
+      return map;
+    }
+
+   private:
+    BacktraceMap* map_ = nullptr;
+    size_t index_ = 0;
+  };
+
+  iterator begin() { return iterator(this, 0); }
+  iterator end() { return iterator(this, maps_.size()); }
+
   // Fill in the map data structure for the given address.
   virtual void FillIn(uintptr_t addr, backtrace_map_t* map);
 
@@ -89,14 +133,6 @@ public:
   virtual void LockIterator() {}
   virtual void UnlockIterator() {}
 
-  typedef std::deque<backtrace_map_t>::iterator iterator;
-  iterator begin() { return maps_.begin(); }
-  iterator end() { return maps_.end(); }
-
-  typedef std::deque<backtrace_map_t>::const_iterator const_iterator;
-  const_iterator begin() const { return maps_.begin(); }
-  const_iterator end() const { return maps_.end(); }
-
   size_t size() const { return maps_.size(); }
 
   virtual bool Build();
@@ -114,6 +150,8 @@ public:
  protected:
   BacktraceMap(pid_t pid);
 
+  virtual uint64_t GetLoadBias(size_t /* index */) { return 0; }
+
   virtual bool ParseLine(const char* line, backtrace_map_t* map);
 
   pid_t pid_;
diff --git a/libunwindstack/Android.bp b/libunwindstack/Android.bp
index 75aa427..74930d6 100644
--- a/libunwindstack/Android.bp
+++ b/libunwindstack/Android.bp
@@ -118,6 +118,7 @@ cc_test {
         "tests/ElfTestUtils.cpp",
         "tests/LogFake.cpp",
         "tests/MapInfoGetElfTest.cpp",
+        "tests/MapInfoGetLoadBiasTest.cpp",
         "tests/MapsTest.cpp",
         "tests/MemoryBufferTest.cpp",
         "tests/MemoryFake.cpp",
diff --git a/libunwindstack/Elf.cpp b/libunwindstack/Elf.cpp
index 97ade56..5f307ed 100644
--- a/libunwindstack/Elf.cpp
+++ b/libunwindstack/Elf.cpp
@@ -215,4 +215,22 @@ ElfInterface* Elf::CreateInterfaceFromMemory(Memory* memory) {
   return interface.release();
 }
 
+uint64_t Elf::GetLoadBias(Memory* memory) {
+  if (!IsValidElf(memory)) {
+    return 0;
+  }
+
+  uint8_t class_type;
+  if (!memory->Read(EI_CLASS, &class_type, 1)) {
+    return 0;
+  }
+
+  if (class_type == ELFCLASS32) {
+    return ElfInterface::GetLoadBias<Elf32_Ehdr, Elf32_Phdr>(memory);
+  } else if (class_type == ELFCLASS64) {
+    return ElfInterface::GetLoadBias<Elf64_Ehdr, Elf64_Phdr>(memory);
+  }
+  return 0;
+}
+
 }  // namespace unwindstack
diff --git a/libunwindstack/ElfInterface.cpp b/libunwindstack/ElfInterface.cpp
index 9bdb094..334cf76 100644
--- a/libunwindstack/ElfInterface.cpp
+++ b/libunwindstack/ElfInterface.cpp
@@ -148,6 +148,26 @@ bool ElfInterface::ReadAllHeaders(uint64_t* load_bias) {
 }
 
 template <typename EhdrType, typename PhdrType>
+uint64_t ElfInterface::GetLoadBias(Memory* memory) {
+  EhdrType ehdr;
+  if (!memory->Read(0, &ehdr, sizeof(ehdr))) {
+    return false;
+  }
+
+  uint64_t offset = ehdr.e_phoff;
+  for (size_t i = 0; i < ehdr.e_phnum; i++, offset += ehdr.e_phentsize) {
+    PhdrType phdr;
+    if (!memory->Read(offset, &phdr, sizeof(phdr))) {
+      return 0;
+    }
+    if (phdr.p_type == PT_LOAD && phdr.p_offset == 0) {
+      return phdr.p_vaddr;
+    }
+  }
+  return 0;
+}
+
+template <typename EhdrType, typename PhdrType>
 bool ElfInterface::ReadProgramHeaders(const EhdrType& ehdr, uint64_t* load_bias) {
   uint64_t offset = ehdr.e_phoff;
   for (size_t i = 0; i < ehdr.e_phnum; i++, offset += ehdr.e_phentsize) {
@@ -421,4 +441,7 @@ template bool ElfInterface::GetFunctionNameWithTemplate<Elf64_Sym>(uint64_t, uin
 template void ElfInterface::GetMaxSizeWithTemplate<Elf32_Ehdr>(Memory*, uint64_t*);
 template void ElfInterface::GetMaxSizeWithTemplate<Elf64_Ehdr>(Memory*, uint64_t*);
 
+template uint64_t ElfInterface::GetLoadBias<Elf32_Ehdr, Elf32_Phdr>(Memory*);
+template uint64_t ElfInterface::GetLoadBias<Elf64_Ehdr, Elf64_Phdr>(Memory*);
+
 }  // namespace unwindstack
diff --git a/libunwindstack/MapInfo.cpp b/libunwindstack/MapInfo.cpp
index 8a7ad9c..51bce8e 100644
--- a/libunwindstack/MapInfo.cpp
+++ b/libunwindstack/MapInfo.cpp
@@ -121,4 +121,23 @@ Elf* MapInfo::GetElf(const std::shared_ptr<Memory>& process_memory, bool init_gn
   return elf;
 }
 
+uint64_t MapInfo::GetLoadBias(const std::shared_ptr<Memory>& process_memory) {
+  {
+    // Make sure no other thread is trying to add the elf to this map.
+    std::lock_guard<std::mutex> guard(mutex_);
+    if (elf != nullptr) {
+      if (elf->valid()) {
+        return elf->GetLoadBias();
+      } else {
+        return 0;
+      }
+    }
+  }
+
+  // Call lightweight static function that will only read enough of the
+  // elf data to get the load bias.
+  std::unique_ptr<Memory> memory(CreateMemory(process_memory));
+  return Elf::GetLoadBias(memory.get());
+}
+
 }  // namespace unwindstack
diff --git a/libunwindstack/include/unwindstack/Elf.h b/libunwindstack/include/unwindstack/Elf.h
index da2ddc0..d9ea9c4 100644
--- a/libunwindstack/include/unwindstack/Elf.h
+++ b/libunwindstack/include/unwindstack/Elf.h
@@ -74,6 +74,8 @@ class Elf {
 
   static void GetInfo(Memory* memory, bool* valid, uint64_t* size);
 
+  static uint64_t GetLoadBias(Memory* memory);
+
  protected:
   bool valid_ = false;
   uint64_t load_bias_ = 0;
diff --git a/libunwindstack/include/unwindstack/ElfInterface.h b/libunwindstack/include/unwindstack/ElfInterface.h
index 86e51b3..5cfe74d 100644
--- a/libunwindstack/include/unwindstack/ElfInterface.h
+++ b/libunwindstack/include/unwindstack/ElfInterface.h
@@ -82,6 +82,9 @@ class ElfInterface {
   DwarfSection* eh_frame() { return eh_frame_.get(); }
   DwarfSection* debug_frame() { return debug_frame_.get(); }
 
+  template <typename EhdrType, typename PhdrType>
+  static uint64_t GetLoadBias(Memory* memory);
+
  protected:
   template <typename AddressType>
   void InitHeadersWithTemplate();
diff --git a/libunwindstack/include/unwindstack/MapInfo.h b/libunwindstack/include/unwindstack/MapInfo.h
index e54b348..6f8ceca 100644
--- a/libunwindstack/include/unwindstack/MapInfo.h
+++ b/libunwindstack/include/unwindstack/MapInfo.h
@@ -51,6 +51,8 @@ struct MapInfo {
   // This function guarantees it will never return nullptr.
   Elf* GetElf(const std::shared_ptr<Memory>& process_memory, bool init_gnu_debugdata = false);
 
+  uint64_t GetLoadBias(const std::shared_ptr<Memory>& process_memory);
+
  private:
   MapInfo(const MapInfo&) = delete;
   void operator=(const MapInfo&) = delete;
diff --git a/libunwindstack/tests/MapInfoGetLoadBiasTest.cpp b/libunwindstack/tests/MapInfoGetLoadBiasTest.cpp
new file mode 100644
index 0000000..44a73a8
--- /dev/null
+++ b/libunwindstack/tests/MapInfoGetLoadBiasTest.cpp
@@ -0,0 +1,150 @@
+/*
+ * Copyright (C) 2016 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 <elf.h>
+#include <errno.h>
+#include <signal.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/ptrace.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <atomic>
+#include <memory>
+#include <thread>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/test_utils.h>
+#include <gtest/gtest.h>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/MapInfo.h>
+#include <unwindstack/Maps.h>
+#include <unwindstack/Memory.h>
+
+#include "ElfFake.h"
+#include "ElfTestUtils.h"
+#include "MemoryFake.h"
+
+namespace unwindstack {
+
+class MapInfoGetLoadBiasTest : public ::testing::Test {
+ protected:
+  void SetUp() override {
+    memory_ = new MemoryFake;
+    process_memory_.reset(memory_);
+    elf_ = new ElfFake(new MemoryFake);
+    elf_container_.reset(elf_);
+    map_info_.reset(new MapInfo(0x1000, 0x20000, 0, PROT_READ | PROT_WRITE, ""));
+  }
+
+  void MultipleThreadTest(uint64_t expected_load_bias);
+
+  std::shared_ptr<Memory> process_memory_;
+  MemoryFake* memory_;
+  ElfFake* elf_;
+  std::unique_ptr<ElfFake> elf_container_;
+  std::unique_ptr<MapInfo> map_info_;
+};
+
+TEST_F(MapInfoGetLoadBiasTest, no_elf_and_no_valid_elf_in_memory) {
+  MapInfo info(0x1000, 0x2000, 0, PROT_READ, "");
+
+  EXPECT_EQ(0U, info.GetLoadBias(process_memory_));
+}
+
+TEST_F(MapInfoGetLoadBiasTest, elf_exists) {
+  map_info_->elf = elf_container_.release();
+
+  elf_->FakeSetLoadBias(0);
+  EXPECT_EQ(0U, map_info_->GetLoadBias(process_memory_));
+
+  elf_->FakeSetLoadBias(0x1000);
+  EXPECT_EQ(0x1000U, map_info_->GetLoadBias(process_memory_));
+}
+
+void MapInfoGetLoadBiasTest::MultipleThreadTest(uint64_t expected_load_bias) {
+  static constexpr size_t kNumConcurrentThreads = 100;
+
+  uint64_t load_bias_values[kNumConcurrentThreads];
+  std::vector<std::thread*> threads;
+
+  std::atomic_bool wait;
+  wait = true;
+  // Create all of the threads and have them do the GetLoadBias at the same time
+  // to make it likely that a race will occur.
+  for (size_t i = 0; i < kNumConcurrentThreads; i++) {
+    std::thread* thread = new std::thread([i, this, &wait, &load_bias_values]() {
+      while (wait)
+        ;
+      load_bias_values[i] = map_info_->GetLoadBias(process_memory_);
+    });
+    threads.push_back(thread);
+  }
+
+  // Set them all going and wait for the threads to finish.
+  wait = false;
+  for (auto thread : threads) {
+    thread->join();
+    delete thread;
+  }
+
+  // Now verify that all of the elf files are exactly the same and valid.
+  for (size_t i = 0; i < kNumConcurrentThreads; i++) {
+    EXPECT_EQ(expected_load_bias, load_bias_values[i]) << "Thread " << i << " mismatched.";
+  }
+}
+
+TEST_F(MapInfoGetLoadBiasTest, multiple_thread_elf_exists) {
+  map_info_->elf = elf_container_.release();
+  elf_->FakeSetLoadBias(0x1000);
+
+  MultipleThreadTest(0x1000);
+}
+
+static void InitElfData(MemoryFake* memory, uint64_t offset) {
+  Elf32_Ehdr ehdr;
+  TestInitEhdr(&ehdr, ELFCLASS32, EM_ARM);
+  ehdr.e_phoff = 0x5000;
+  ehdr.e_phnum = 2;
+  ehdr.e_phentsize = sizeof(Elf32_Phdr);
+  memory->SetMemory(offset, &ehdr, sizeof(ehdr));
+
+  Elf32_Phdr phdr;
+  memset(&phdr, 0, sizeof(phdr));
+  phdr.p_type = PT_NULL;
+  memory->SetMemory(offset + 0x5000, &phdr, sizeof(phdr));
+  phdr.p_type = PT_LOAD;
+  phdr.p_offset = 0;
+  phdr.p_vaddr = 0xe000;
+  memory->SetMemory(offset + 0x5000 + sizeof(phdr), &phdr, sizeof(phdr));
+}
+
+TEST_F(MapInfoGetLoadBiasTest, elf_exists_in_memory) {
+  InitElfData(memory_, map_info_->start);
+
+  EXPECT_EQ(0xe000U, map_info_->GetLoadBias(process_memory_));
+}
+
+TEST_F(MapInfoGetLoadBiasTest, multiple_thread_elf_exists_in_memory) {
+  InitElfData(memory_, map_info_->start);
+
+  MultipleThreadTest(0xe000);
+}
+
+}  // namespace unwindstack