libmemunreachable/MemUnreachable.cpp - platform/system/core - Gitiles

 /*
  * 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 <inttypes.h>
 #include <string.h>

 #include <functional>
 #include <iomanip>
 #include <mutex>
 #include <sstream>
 #include <string>
 #include <unordered_map>

 #include <android-base/macros.h>
 #include <backtrace.h>

 #include "Allocator.h"
 #include "HeapWalker.h"
 #include "Leak.h"
 #include "LeakFolding.h"
 #include "LeakPipe.h"
 #include "ProcessMappings.h"
 #include "PtracerThread.h"
 #include "ScopedDisableMalloc.h"
 #include "Semaphore.h"
 #include "ThreadCapture.h"

 #include "bionic.h"
 #include "log.h"
 #include "memunreachable/memunreachable.h"

 using namespace std::chrono_literals;

 namespace android {

 const size_t Leak::contents_length;

 class MemUnreachable {
  public:
   MemUnreachable(pid_t pid, Allocator<void> allocator)
       : pid_(pid), allocator_(allocator), heap_walker_(allocator_) {}
   bool CollectAllocations(const allocator::vector<ThreadInfo>& threads,
                           const allocator::vector<Mapping>& mappings);
   bool GetUnreachableMemory(allocator::vector<Leak>& leaks, size_t limit, size_t* num_leaks,
                             size_t* leak_bytes);
   size_t Allocations() { return heap_walker_.Allocations(); }
   size_t AllocationBytes() { return heap_walker_.AllocationBytes(); }

  private:
   bool ClassifyMappings(const allocator::vector<Mapping>& mappings,
                         allocator::vector<Mapping>& heap_mappings,
                         allocator::vector<Mapping>& anon_mappings,
                         allocator::vector<Mapping>& globals_mappings,
                         allocator::vector<Mapping>& stack_mappings);
   DISALLOW_COPY_AND_ASSIGN(MemUnreachable);
   pid_t pid_;
   Allocator<void> allocator_;
   HeapWalker heap_walker_;
 };

 static void HeapIterate(const Mapping& heap_mapping,
                         const std::function<void(uintptr_t, size_t)>& func) {
   malloc_iterate(heap_mapping.begin, heap_mapping.end - heap_mapping.begin,
                  [](uintptr_t base, size_t size, void* arg) {
                    auto f = reinterpret_cast<const std::function<void(uintptr_t, size_t)>*>(arg);
                    (*f)(base, size);
                  },
                  const_cast<void*>(reinterpret_cast<const void*>(&func)));
 }

 bool MemUnreachable::CollectAllocations(const allocator::vector<ThreadInfo>& threads,
                                         const allocator::vector<Mapping>& mappings) {
   MEM_ALOGI("searching process %d for allocations", pid_);
   allocator::vector<Mapping> heap_mappings{mappings};
   allocator::vector<Mapping> anon_mappings{mappings};
   allocator::vector<Mapping> globals_mappings{mappings};
   allocator::vector<Mapping> stack_mappings{mappings};
   if (!ClassifyMappings(mappings, heap_mappings, anon_mappings, globals_mappings, stack_mappings)) {
     return false;
   }

   for (auto it = heap_mappings.begin(); it != heap_mappings.end(); it++) {
     MEM_ALOGV("Heap mapping %" PRIxPTR "-%" PRIxPTR " %s", it->begin, it->end, it->name);
     HeapIterate(*it,
                 [&](uintptr_t base, size_t size) { heap_walker_.Allocation(base, base + size); });
   }

   for (auto it = anon_mappings.begin(); it != anon_mappings.end(); it++) {
     MEM_ALOGV("Anon mapping %" PRIxPTR "-%" PRIxPTR " %s", it->begin, it->end, it->name);
     heap_walker_.Allocation(it->begin, it->end);
   }

   for (auto it = globals_mappings.begin(); it != globals_mappings.end(); it++) {
     MEM_ALOGV("Globals mapping %" PRIxPTR "-%" PRIxPTR " %s", it->begin, it->end, it->name);
     heap_walker_.Root(it->begin, it->end);
   }

   for (auto thread_it = threads.begin(); thread_it != threads.end(); thread_it++) {
     for (auto it = stack_mappings.begin(); it != stack_mappings.end(); it++) {
       if (thread_it->stack.first >= it->begin && thread_it->stack.first <= it->end) {
         MEM_ALOGV("Stack %" PRIxPTR "-%" PRIxPTR " %s", thread_it->stack.first, it->end, it->name);
         heap_walker_.Root(thread_it->stack.first, it->end);
       }
     }
     heap_walker_.Root(thread_it->regs);
   }

   MEM_ALOGI("searching done");

   return true;
 }

 bool MemUnreachable::GetUnreachableMemory(allocator::vector<Leak>& leaks, size_t limit,
                                           size_t* num_leaks, size_t* leak_bytes) {
   MEM_ALOGI("sweeping process %d for unreachable memory", pid_);
   leaks.clear();

   if (!heap_walker_.DetectLeaks()) {
     return false;
   }

   allocator::vector<Range> leaked1{allocator_};
   heap_walker_.Leaked(leaked1, 0, num_leaks, leak_bytes);

   MEM_ALOGI("sweeping done");

   MEM_ALOGI("folding related leaks");

   LeakFolding folding(allocator_, heap_walker_);
   if (!folding.FoldLeaks()) {
     return false;
   }

   allocator::vector<LeakFolding::Leak> leaked{allocator_};

   if (!folding.Leaked(leaked, num_leaks, leak_bytes)) {
     return false;
   }

   allocator::unordered_map<Leak::Backtrace, Leak*> backtrace_map{allocator_};

   // Prevent reallocations of backing memory so we can store pointers into it
   // in backtrace_map.
   leaks.reserve(leaked.size());

   for (auto& it : leaked) {
     leaks.emplace_back();
     Leak* leak = &leaks.back();

     ssize_t num_backtrace_frames = malloc_backtrace(
         reinterpret_cast<void*>(it.range.begin), leak->backtrace.frames, leak->backtrace.max_frames);
     if (num_backtrace_frames > 0) {
       leak->backtrace.num_frames = num_backtrace_frames;

       auto inserted = backtrace_map.emplace(leak->backtrace, leak);
       if (!inserted.second) {
         // Leak with same backtrace already exists, drop this one and
         // increment similar counts on the existing one.
         leaks.pop_back();
         Leak* similar_leak = inserted.first->second;
         similar_leak->similar_count++;
         similar_leak->similar_size += it.range.size();
         similar_leak->similar_referenced_count += it.referenced_count;
         similar_leak->similar_referenced_size += it.referenced_size;
         similar_leak->total_size += it.range.size();
         similar_leak->total_size += it.referenced_size;
         continue;
       }
     }

     leak->begin = it.range.begin;
     leak->size = it.range.size();
     leak->referenced_count = it.referenced_count;
     leak->referenced_size = it.referenced_size;
     leak->total_size = leak->size + leak->referenced_size;
     memcpy(leak->contents, reinterpret_cast<void*>(it.range.begin),
            std::min(leak->size, Leak::contents_length));
   }

   MEM_ALOGI("folding done");

   std::sort(leaks.begin(), leaks.end(),
             [](const Leak& a, const Leak& b) { return a.total_size > b.total_size; });

   if (leaks.size() > limit) {
     leaks.resize(limit);
   }

   return true;
 }

 static bool has_prefix(const allocator::string& s, const char* prefix) {
   int ret = s.compare(0, strlen(prefix), prefix);
   return ret == 0;
 }

 bool MemUnreachable::ClassifyMappings(const allocator::vector<Mapping>& mappings,
                                       allocator::vector<Mapping>& heap_mappings,
                                       allocator::vector<Mapping>& anon_mappings,
                                       allocator::vector<Mapping>& globals_mappings,
                                       allocator::vector<Mapping>& stack_mappings) {
   heap_mappings.clear();
   anon_mappings.clear();
   globals_mappings.clear();
   stack_mappings.clear();

   allocator::string current_lib{allocator_};

   for (auto it = mappings.begin(); it != mappings.end(); it++) {
     if (it->execute) {
       current_lib = it->name;
       continue;
     }

     if (!it->read) {
       continue;
     }

     const allocator::string mapping_name{it->name, allocator_};
     if (mapping_name == "[anon:.bss]") {
       // named .bss section
       globals_mappings.emplace_back(*it);
     } else if (mapping_name == current_lib) {
       // .rodata or .data section
       globals_mappings.emplace_back(*it);
     } else if (mapping_name == "[anon:libc_malloc]") {
       // named malloc mapping
       heap_mappings.emplace_back(*it);
     } else if (has_prefix(mapping_name, "/dev/ashmem/dalvik")) {
       // named dalvik heap mapping
       globals_mappings.emplace_back(*it);
     } else if (has_prefix(mapping_name, "[stack")) {
       // named stack mapping
       stack_mappings.emplace_back(*it);
     } else if (mapping_name.size() == 0) {
       globals_mappings.emplace_back(*it);
     } else if (has_prefix(mapping_name, "[anon:") &&
                mapping_name != "[anon:leak_detector_malloc]") {
       // TODO(ccross): it would be nice to treat named anonymous mappings as
       // possible leaks, but naming something in a .bss or .data section makes
       // it impossible to distinguish them from mmaped and then named mappings.
       globals_mappings.emplace_back(*it);
     }
   }

   return true;
 }

 template <typename T>
 static inline const char* plural(T val) {
   return (val == 1) ? "" : "s";
 }

 bool GetUnreachableMemory(UnreachableMemoryInfo& info, size_t limit) {
   int parent_pid = getpid();
   int parent_tid = gettid();

   Heap heap;

   Semaphore continue_parent_sem;
   LeakPipe pipe;

   PtracerThread thread{[&]() -> int {
     /////////////////////////////////////////////
     // Collection thread
     /////////////////////////////////////////////
     MEM_ALOGI("collecting thread info for process %d...", parent_pid);

     ThreadCapture thread_capture(parent_pid, heap);
     allocator::vector<ThreadInfo> thread_info(heap);
     allocator::vector<Mapping> mappings(heap);

     // ptrace all the threads
     if (!thread_capture.CaptureThreads()) {
       continue_parent_sem.Post();
       return 1;
     }

     // collect register contents and stacks
     if (!thread_capture.CapturedThreadInfo(thread_info)) {
       continue_parent_sem.Post();
       return 1;
     }

     // snapshot /proc/pid/maps
     if (!ProcessMappings(parent_pid, mappings)) {
       continue_parent_sem.Post();
       return 1;
     }

     // malloc must be enabled to call fork, at_fork handlers take the same
     // locks as ScopedDisableMalloc.  All threads are paused in ptrace, so
     // memory state is still consistent.  Unfreeze the original thread so it
     // can drop the malloc locks, it will block until the collection thread
     // exits.
     thread_capture.ReleaseThread(parent_tid);
     continue_parent_sem.Post();

     // fork a process to do the heap walking
     int ret = fork();
     if (ret < 0) {
       return 1;
     } else if (ret == 0) {
       /////////////////////////////////////////////
       // Heap walker process
       /////////////////////////////////////////////
       // Examine memory state in the child using the data collected above and
       // the CoW snapshot of the process memory contents.

       if (!pipe.OpenSender()) {
         _exit(1);
       }

       MemUnreachable unreachable{parent_pid, heap};

       if (!unreachable.CollectAllocations(thread_info, mappings)) {
         _exit(2);
       }
       size_t num_allocations = unreachable.Allocations();
       size_t allocation_bytes = unreachable.AllocationBytes();

       allocator::vector<Leak> leaks{heap};

       size_t num_leaks = 0;
       size_t leak_bytes = 0;
       bool ok = unreachable.GetUnreachableMemory(leaks, limit, &num_leaks, &leak_bytes);

       ok = ok && pipe.Sender().Send(num_allocations);
       ok = ok && pipe.Sender().Send(allocation_bytes);
       ok = ok && pipe.Sender().Send(num_leaks);
       ok = ok && pipe.Sender().Send(leak_bytes);
       ok = ok && pipe.Sender().SendVector(leaks);

       if (!ok) {
         _exit(3);
       }

       _exit(0);
     } else {
       // Nothing left to do in the collection thread, return immediately,
       // releasing all the captured threads.
       MEM_ALOGI("collection thread done");
       return 0;
     }
   }};

   /////////////////////////////////////////////
   // Original thread
   /////////////////////////////////////////////

   {
     // Disable malloc to get a consistent view of memory
     ScopedDisableMalloc disable_malloc;

     // Start the collection thread
     thread.Start();

     // Wait for the collection thread to signal that it is ready to fork the
     // heap walker process.
     continue_parent_sem.Wait(30s);

     // Re-enable malloc so the collection thread can fork.
   }

   // Wait for the collection thread to exit
   int ret = thread.Join();
   if (ret != 0) {
     return false;
   }

   // Get a pipe from the heap walker process.  Transferring a new pipe fd
   // ensures no other forked processes can have it open, so when the heap
   // walker process dies the remote side of the pipe will close.
   if (!pipe.OpenReceiver()) {
     return false;
   }

   bool ok = true;
   ok = ok && pipe.Receiver().Receive(&info.num_allocations);
   ok = ok && pipe.Receiver().Receive(&info.allocation_bytes);
   ok = ok && pipe.Receiver().Receive(&info.num_leaks);
   ok = ok && pipe.Receiver().Receive(&info.leak_bytes);
   ok = ok && pipe.Receiver().ReceiveVector(info.leaks);
   if (!ok) {
     return false;
   }

   MEM_ALOGI("unreachable memory detection done");
   MEM_ALOGE("%zu bytes in %zu allocation%s unreachable out of %zu bytes in %zu allocation%s",
             info.leak_bytes, info.num_leaks, plural(info.num_leaks), info.allocation_bytes,
             info.num_allocations, plural(info.num_allocations));
   return true;
 }

 std::string Leak::ToString(bool log_contents) const {
   std::ostringstream oss;

   oss << "  " << std::dec << size;
   oss << " bytes unreachable at ";
   oss << std::hex << begin;
   oss << std::endl;
   if (referenced_count > 0) {
     oss << std::dec;
     oss << "   referencing " << referenced_size << " unreachable bytes";
     oss << " in " << referenced_count << " allocation" << plural(referenced_count);
     oss << std::endl;
   }
   if (similar_count > 0) {
     oss << std::dec;
     oss << "   and " << similar_size << " similar unreachable bytes";
     oss << " in " << similar_count << " allocation" << plural(similar_count);
     oss << std::endl;
     if (similar_referenced_count > 0) {
       oss << "   referencing " << similar_referenced_size << " unreachable bytes";
       oss << " in " << similar_referenced_count << " allocation" << plural(similar_referenced_count);
       oss << std::endl;
     }
   }

   if (log_contents) {
     const int bytes_per_line = 16;
     const size_t bytes = std::min(size, contents_length);

     if (bytes == size) {
       oss << "   contents:" << std::endl;
     } else {
       oss << "   first " << bytes << " bytes of contents:" << std::endl;
     }

     for (size_t i = 0; i < bytes; i += bytes_per_line) {
       oss << "   " << std::hex << begin + i << ": ";
       size_t j;
       oss << std::setfill('0');
       for (j = i; j < bytes && j < i + bytes_per_line; j++) {
         oss << std::setw(2) << static_cast<int>(contents[j]) << " ";
       }
       oss << std::setfill(' ');
       for (; j < i + bytes_per_line; j++) {
         oss << "   ";
       }
       for (j = i; j < bytes && j < i + bytes_per_line; j++) {
         char c = contents[j];
         if (c < ' ' || c >= 0x7f) {
           c = '.';
         }
         oss << c;
       }
       oss << std::endl;
     }
   }
   if (backtrace.num_frames > 0) {
     oss << backtrace_string(backtrace.frames, backtrace.num_frames);
   }

   return oss.str();
 }

 // Figure out the abi based on defined macros.
 #if defined(__arm__)
 #define ABI_STRING "arm"
 #elif defined(__aarch64__)
 #define ABI_STRING "arm64"
 #elif defined(__mips__) && !defined(__LP64__)
 #define ABI_STRING "mips"
 #elif defined(__mips__) && defined(__LP64__)
 #define ABI_STRING "mips64"
 #elif defined(__i386__)
 #define ABI_STRING "x86"
 #elif defined(__x86_64__)
 #define ABI_STRING "x86_64"
 #else
 #error "Unsupported ABI"
 #endif

 std::string UnreachableMemoryInfo::ToString(bool log_contents) const {
   std::ostringstream oss;
   oss << "  " << leak_bytes << " bytes in ";
   oss << num_leaks << " unreachable allocation" << plural(num_leaks);
   oss << std::endl;
   oss << "  ABI: '" ABI_STRING "'" << std::endl;
   oss << std::endl;

   for (auto it = leaks.begin(); it != leaks.end(); it++) {
     oss << it->ToString(log_contents);
     oss << std::endl;
   }

   return oss.str();
 }

 std::string GetUnreachableMemoryString(bool log_contents, size_t limit) {
   UnreachableMemoryInfo info;
   if (!GetUnreachableMemory(info, limit)) {
     return "Failed to get unreachable memory\n"
            "If you are trying to get unreachable memory from a system app\n"
            "(like com.android.systemui), disable selinux first using\n"
            "setenforce 0\n";
   }

   return info.ToString(log_contents);
 }

 }  // namespace android

 bool LogUnreachableMemory(bool log_contents, size_t limit) {
   android::UnreachableMemoryInfo info;
   if (!android::GetUnreachableMemory(info, limit)) {
     return false;
   }

   for (auto it = info.leaks.begin(); it != info.leaks.end(); it++) {
     MEM_ALOGE("%s", it->ToString(log_contents).c_str());
   }
   return true;
 }

 bool NoLeaks() {
   android::UnreachableMemoryInfo info;
   if (!android::GetUnreachableMemory(info, 0)) {
     return false;
   }

   return info.num_leaks == 0;
 }
	/*
	* 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 <inttypes.h>
	#include <string.h>

	#include <functional>
	#include <iomanip>
	#include <mutex>
	#include <sstream>
	#include <string>
	#include <unordered_map>

	#include <android-base/macros.h>
	#include <backtrace.h>

	#include "Allocator.h"
	#include "HeapWalker.h"
	#include "Leak.h"
	#include "LeakFolding.h"
	#include "LeakPipe.h"
	#include "ProcessMappings.h"
	#include "PtracerThread.h"
	#include "ScopedDisableMalloc.h"
	#include "Semaphore.h"
	#include "ThreadCapture.h"

	#include "bionic.h"
	#include "log.h"
	#include "memunreachable/memunreachable.h"

	using namespace std::chrono_literals;

	namespace android {

	const size_t Leak::contents_length;

	class MemUnreachable {
	public:
	MemUnreachable(pid_t pid, Allocator<void> allocator)
	: pid_(pid), allocator_(allocator), heap_walker_(allocator_) {}
	bool CollectAllocations(const allocator::vector<ThreadInfo>& threads,
	const allocator::vector<Mapping>& mappings);
	bool GetUnreachableMemory(allocator::vector<Leak>& leaks, size_t limit, size_t* num_leaks,
	size_t* leak_bytes);
	size_t Allocations() { return heap_walker_.Allocations(); }
	size_t AllocationBytes() { return heap_walker_.AllocationBytes(); }

	private:
	bool ClassifyMappings(const allocator::vector<Mapping>& mappings,
	allocator::vector<Mapping>& heap_mappings,
	allocator::vector<Mapping>& anon_mappings,
	allocator::vector<Mapping>& globals_mappings,
	allocator::vector<Mapping>& stack_mappings);
	DISALLOW_COPY_AND_ASSIGN(MemUnreachable);
	pid_t pid_;
	Allocator<void> allocator_;
	HeapWalker heap_walker_;
	};

	static void HeapIterate(const Mapping& heap_mapping,
	const std::function<void(uintptr_t, size_t)>& func) {
	malloc_iterate(heap_mapping.begin, heap_mapping.end - heap_mapping.begin,
	[](uintptr_t base, size_t size, void* arg) {
	auto f = reinterpret_cast<const std::function<void(uintptr_t, size_t)>*>(arg);
	(*f)(base, size);
	},
	const_cast<void>(reinterpret_cast<const void>(&func)));
	}

	bool MemUnreachable::CollectAllocations(const allocator::vector<ThreadInfo>& threads,
	const allocator::vector<Mapping>& mappings) {
	MEM_ALOGI("searching process %d for allocations", pid_);
	allocator::vector<Mapping> heap_mappings{mappings};
	allocator::vector<Mapping> anon_mappings{mappings};
	allocator::vector<Mapping> globals_mappings{mappings};
	allocator::vector<Mapping> stack_mappings{mappings};
	if (!ClassifyMappings(mappings, heap_mappings, anon_mappings, globals_mappings, stack_mappings)) {
	return false;
	}

	for (auto it = heap_mappings.begin(); it != heap_mappings.end(); it++) {
	MEM_ALOGV("Heap mapping %" PRIxPTR "-%" PRIxPTR " %s", it->begin, it->end, it->name);
	HeapIterate(*it,
	[&](uintptr_t base, size_t size) { heap_walker_.Allocation(base, base + size); });
	}

	for (auto it = anon_mappings.begin(); it != anon_mappings.end(); it++) {
	MEM_ALOGV("Anon mapping %" PRIxPTR "-%" PRIxPTR " %s", it->begin, it->end, it->name);
	heap_walker_.Allocation(it->begin, it->end);
	}

	for (auto it = globals_mappings.begin(); it != globals_mappings.end(); it++) {
	MEM_ALOGV("Globals mapping %" PRIxPTR "-%" PRIxPTR " %s", it->begin, it->end, it->name);
	heap_walker_.Root(it->begin, it->end);
	}

	for (auto thread_it = threads.begin(); thread_it != threads.end(); thread_it++) {
	for (auto it = stack_mappings.begin(); it != stack_mappings.end(); it++) {
	if (thread_it->stack.first >= it->begin && thread_it->stack.first <= it->end) {
	MEM_ALOGV("Stack %" PRIxPTR "-%" PRIxPTR " %s", thread_it->stack.first, it->end, it->name);
	heap_walker_.Root(thread_it->stack.first, it->end);
	}
	}
	heap_walker_.Root(thread_it->regs);
	}

	MEM_ALOGI("searching done");

	return true;
	}

	bool MemUnreachable::GetUnreachableMemory(allocator::vector<Leak>& leaks, size_t limit,
	size_t* num_leaks, size_t* leak_bytes) {
	MEM_ALOGI("sweeping process %d for unreachable memory", pid_);
	leaks.clear();

	if (!heap_walker_.DetectLeaks()) {
	return false;
	}

	allocator::vector<Range> leaked1{allocator_};
	heap_walker_.Leaked(leaked1, 0, num_leaks, leak_bytes);

	MEM_ALOGI("sweeping done");

	MEM_ALOGI("folding related leaks");

	LeakFolding folding(allocator_, heap_walker_);
	if (!folding.FoldLeaks()) {
	return false;
	}

	allocator::vector<LeakFolding::Leak> leaked{allocator_};

	if (!folding.Leaked(leaked, num_leaks, leak_bytes)) {
	return false;
	}

	allocator::unordered_map<Leak::Backtrace, Leak*> backtrace_map{allocator_};

	// Prevent reallocations of backing memory so we can store pointers into it
	// in backtrace_map.
	leaks.reserve(leaked.size());

	for (auto& it : leaked) {
	leaks.emplace_back();
	Leak* leak = &leaks.back();

	ssize_t num_backtrace_frames = malloc_backtrace(
	reinterpret_cast<void*>(it.range.begin), leak->backtrace.frames, leak->backtrace.max_frames);
	if (num_backtrace_frames > 0) {
	leak->backtrace.num_frames = num_backtrace_frames;

	auto inserted = backtrace_map.emplace(leak->backtrace, leak);
	if (!inserted.second) {
	// Leak with same backtrace already exists, drop this one and
	// increment similar counts on the existing one.
	leaks.pop_back();
	Leak* similar_leak = inserted.first->second;
	similar_leak->similar_count++;
	similar_leak->similar_size += it.range.size();
	similar_leak->similar_referenced_count += it.referenced_count;
	similar_leak->similar_referenced_size += it.referenced_size;
	similar_leak->total_size += it.range.size();
	similar_leak->total_size += it.referenced_size;
	continue;
	}
	}

	leak->begin = it.range.begin;
	leak->size = it.range.size();
	leak->referenced_count = it.referenced_count;
	leak->referenced_size = it.referenced_size;
	leak->total_size = leak->size + leak->referenced_size;
	memcpy(leak->contents, reinterpret_cast<void*>(it.range.begin),
	std::min(leak->size, Leak::contents_length));
	}

	MEM_ALOGI("folding done");

	std::sort(leaks.begin(), leaks.end(),
	[](const Leak& a, const Leak& b) { return a.total_size > b.total_size; });

	if (leaks.size() > limit) {
	leaks.resize(limit);
	}

	return true;
	}

	static bool has_prefix(const allocator::string& s, const char* prefix) {
	int ret = s.compare(0, strlen(prefix), prefix);
	return ret == 0;
	}

	bool MemUnreachable::ClassifyMappings(const allocator::vector<Mapping>& mappings,
	allocator::vector<Mapping>& heap_mappings,
	allocator::vector<Mapping>& anon_mappings,
	allocator::vector<Mapping>& globals_mappings,
	allocator::vector<Mapping>& stack_mappings) {
	heap_mappings.clear();
	anon_mappings.clear();
	globals_mappings.clear();
	stack_mappings.clear();

	allocator::string current_lib{allocator_};

	for (auto it = mappings.begin(); it != mappings.end(); it++) {
	if (it->execute) {
	current_lib = it->name;
	continue;
	}

	if (!it->read) {
	continue;
	}

	const allocator::string mapping_name{it->name, allocator_};
	if (mapping_name == "[anon:.bss]") {
	// named .bss section
	globals_mappings.emplace_back(*it);
	} else if (mapping_name == current_lib) {
	// .rodata or .data section
	globals_mappings.emplace_back(*it);
	} else if (mapping_name == "[anon:libc_malloc]") {
	// named malloc mapping
	heap_mappings.emplace_back(*it);
	} else if (has_prefix(mapping_name, "/dev/ashmem/dalvik")) {
	// named dalvik heap mapping
	globals_mappings.emplace_back(*it);
	} else if (has_prefix(mapping_name, "[stack")) {
	// named stack mapping
	stack_mappings.emplace_back(*it);
	} else if (mapping_name.size() == 0) {
	globals_mappings.emplace_back(*it);
	} else if (has_prefix(mapping_name, "[anon:") &&
	mapping_name != "[anon:leak_detector_malloc]") {
	// TODO(ccross): it would be nice to treat named anonymous mappings as
	// possible leaks, but naming something in a .bss or .data section makes
	// it impossible to distinguish them from mmaped and then named mappings.
	globals_mappings.emplace_back(*it);
	}
	}

	return true;
	}

	template <typename T>
	static inline const char* plural(T val) {
	return (val == 1) ? "" : "s";
	}

	bool GetUnreachableMemory(UnreachableMemoryInfo& info, size_t limit) {
	int parent_pid = getpid();
	int parent_tid = gettid();

	Heap heap;

	Semaphore continue_parent_sem;
	LeakPipe pipe;

	PtracerThread thread{[&]() -> int {
	/////////////////////////////////////////////
	// Collection thread
	/////////////////////////////////////////////
	MEM_ALOGI("collecting thread info for process %d...", parent_pid);

	ThreadCapture thread_capture(parent_pid, heap);
	allocator::vector<ThreadInfo> thread_info(heap);
	allocator::vector<Mapping> mappings(heap);

	// ptrace all the threads
	if (!thread_capture.CaptureThreads()) {
	continue_parent_sem.Post();
	return 1;
	}

	// collect register contents and stacks
	if (!thread_capture.CapturedThreadInfo(thread_info)) {
	continue_parent_sem.Post();
	return 1;
	}

	// snapshot /proc/pid/maps
	if (!ProcessMappings(parent_pid, mappings)) {
	continue_parent_sem.Post();
	return 1;
	}

	// malloc must be enabled to call fork, at_fork handlers take the same
	// locks as ScopedDisableMalloc. All threads are paused in ptrace, so
	// memory state is still consistent. Unfreeze the original thread so it
	// can drop the malloc locks, it will block until the collection thread
	// exits.
	thread_capture.ReleaseThread(parent_tid);
	continue_parent_sem.Post();

	// fork a process to do the heap walking
	int ret = fork();
	if (ret < 0) {
	return 1;
	} else if (ret == 0) {
	/////////////////////////////////////////////
	// Heap walker process
	/////////////////////////////////////////////
	// Examine memory state in the child using the data collected above and
	// the CoW snapshot of the process memory contents.

	if (!pipe.OpenSender()) {
	_exit(1);
	}

	MemUnreachable unreachable{parent_pid, heap};

	if (!unreachable.CollectAllocations(thread_info, mappings)) {
	_exit(2);
	}
	size_t num_allocations = unreachable.Allocations();
	size_t allocation_bytes = unreachable.AllocationBytes();

	allocator::vector<Leak> leaks{heap};

	size_t num_leaks = 0;
	size_t leak_bytes = 0;
	bool ok = unreachable.GetUnreachableMemory(leaks, limit, &num_leaks, &leak_bytes);

	ok = ok && pipe.Sender().Send(num_allocations);
	ok = ok && pipe.Sender().Send(allocation_bytes);
	ok = ok && pipe.Sender().Send(num_leaks);
	ok = ok && pipe.Sender().Send(leak_bytes);
	ok = ok && pipe.Sender().SendVector(leaks);

	if (!ok) {
	_exit(3);
	}

	_exit(0);
	} else {
	// Nothing left to do in the collection thread, return immediately,
	// releasing all the captured threads.
	MEM_ALOGI("collection thread done");
	return 0;
	}
	}};

	/////////////////////////////////////////////
	// Original thread
	/////////////////////////////////////////////

	{
	// Disable malloc to get a consistent view of memory
	ScopedDisableMalloc disable_malloc;

	// Start the collection thread
	thread.Start();

	// Wait for the collection thread to signal that it is ready to fork the
	// heap walker process.
	continue_parent_sem.Wait(30s);

	// Re-enable malloc so the collection thread can fork.
	}

	// Wait for the collection thread to exit
	int ret = thread.Join();
	if (ret != 0) {
	return false;
	}

	// Get a pipe from the heap walker process. Transferring a new pipe fd
	// ensures no other forked processes can have it open, so when the heap
	// walker process dies the remote side of the pipe will close.
	if (!pipe.OpenReceiver()) {
	return false;
	}

	bool ok = true;
	ok = ok && pipe.Receiver().Receive(&info.num_allocations);
	ok = ok && pipe.Receiver().Receive(&info.allocation_bytes);
	ok = ok && pipe.Receiver().Receive(&info.num_leaks);
	ok = ok && pipe.Receiver().Receive(&info.leak_bytes);
	ok = ok && pipe.Receiver().ReceiveVector(info.leaks);
	if (!ok) {
	return false;
	}

	MEM_ALOGI("unreachable memory detection done");
	MEM_ALOGE("%zu bytes in %zu allocation%s unreachable out of %zu bytes in %zu allocation%s",
	info.leak_bytes, info.num_leaks, plural(info.num_leaks), info.allocation_bytes,
	info.num_allocations, plural(info.num_allocations));
	return true;
	}

	std::string Leak::ToString(bool log_contents) const {
	std::ostringstream oss;

	oss << " " << std::dec << size;
	oss << " bytes unreachable at ";
	oss << std::hex << begin;
	oss << std::endl;
	if (referenced_count > 0) {
	oss << std::dec;
	oss << " referencing " << referenced_size << " unreachable bytes";
	oss << " in " << referenced_count << " allocation" << plural(referenced_count);
	oss << std::endl;
	}
	if (similar_count > 0) {
	oss << std::dec;
	oss << " and " << similar_size << " similar unreachable bytes";
	oss << " in " << similar_count << " allocation" << plural(similar_count);
	oss << std::endl;
	if (similar_referenced_count > 0) {
	oss << " referencing " << similar_referenced_size << " unreachable bytes";
	oss << " in " << similar_referenced_count << " allocation" << plural(similar_referenced_count);
	oss << std::endl;
	}
	}

	if (log_contents) {
	const int bytes_per_line = 16;
	const size_t bytes = std::min(size, contents_length);

	if (bytes == size) {
	oss << " contents:" << std::endl;
	} else {
	oss << " first " << bytes << " bytes of contents:" << std::endl;
	}

	for (size_t i = 0; i < bytes; i += bytes_per_line) {
	oss << " " << std::hex << begin + i << ": ";
	size_t j;
	oss << std::setfill('0');
	for (j = i; j < bytes && j < i + bytes_per_line; j++) {
	oss << std::setw(2) << static_cast<int>(contents[j]) << " ";
	}
	oss << std::setfill(' ');
	for (; j < i + bytes_per_line; j++) {
	oss << " ";
	}
	for (j = i; j < bytes && j < i + bytes_per_line; j++) {
	char c = contents[j];
	if (c < ' ' \|\| c >= 0x7f) {
	c = '.';
	}
	oss << c;
	}
	oss << std::endl;
	}
	}
	if (backtrace.num_frames > 0) {
	oss << backtrace_string(backtrace.frames, backtrace.num_frames);
	}

	return oss.str();
	}

	// Figure out the abi based on defined macros.
	#if defined(__arm__)
	#define ABI_STRING "arm"
	#elif defined(__aarch64__)
	#define ABI_STRING "arm64"
	#elif defined(__mips__) && !defined(__LP64__)
	#define ABI_STRING "mips"
	#elif defined(__mips__) && defined(__LP64__)
	#define ABI_STRING "mips64"
	#elif defined(__i386__)
	#define ABI_STRING "x86"
	#elif defined(__x86_64__)
	#define ABI_STRING "x86_64"
	#else
	#error "Unsupported ABI"
	#endif

	std::string UnreachableMemoryInfo::ToString(bool log_contents) const {
	std::ostringstream oss;
	oss << " " << leak_bytes << " bytes in ";
	oss << num_leaks << " unreachable allocation" << plural(num_leaks);
	oss << std::endl;
	oss << " ABI: '" ABI_STRING "'" << std::endl;
	oss << std::endl;

	for (auto it = leaks.begin(); it != leaks.end(); it++) {
	oss << it->ToString(log_contents);
	oss << std::endl;
	}

	return oss.str();
	}

	std::string GetUnreachableMemoryString(bool log_contents, size_t limit) {
	UnreachableMemoryInfo info;
	if (!GetUnreachableMemory(info, limit)) {
	return "Failed to get unreachable memory\n"
	"If you are trying to get unreachable memory from a system app\n"
	"(like com.android.systemui), disable selinux first using\n"
	"setenforce 0\n";
	}

	return info.ToString(log_contents);
	}

	} // namespace android

	bool LogUnreachableMemory(bool log_contents, size_t limit) {
	android::UnreachableMemoryInfo info;
	if (!android::GetUnreachableMemory(info, limit)) {
	return false;
	}

	for (auto it = info.leaks.begin(); it != info.leaks.end(); it++) {
	MEM_ALOGE("%s", it->ToString(log_contents).c_str());
	}
	return true;
	}

	bool NoLeaks() {
	android::UnreachableMemoryInfo info;
	if (!android::GetUnreachableMemory(info, 0)) {
	return false;
	}

	return info.num_leaks == 0;
	}