libunwindstack/Memory.cpp - LeafOS-Project/android_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 <errno.h>
 #include <fcntl.h>
 #include <string.h>
 #include <sys/mman.h>
 #include <sys/ptrace.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/uio.h>
 #include <unistd.h>

 #include <algorithm>
 #include <memory>

 #include <android-base/unique_fd.h>

 #include <unwindstack/Memory.h>

 #include "Check.h"
 #include "MemoryBuffer.h"
 #include "MemoryCache.h"
 #include "MemoryFileAtOffset.h"
 #include "MemoryLocal.h"
 #include "MemoryOffline.h"
 #include "MemoryOfflineBuffer.h"
 #include "MemoryRange.h"
 #include "MemoryRemote.h"

 namespace unwindstack {

 static size_t ProcessVmRead(pid_t pid, uint64_t remote_src, void* dst, size_t len) {

   // Split up the remote read across page boundaries.
   // From the manpage:
   //   A partial read/write may result if one of the remote_iov elements points to an invalid
   //   memory region in the remote process.
   //
   //   Partial transfers apply at the granularity of iovec elements.  These system calls won't
   //   perform a partial transfer that splits a single iovec element.
   constexpr size_t kMaxIovecs = 64;
   struct iovec src_iovs[kMaxIovecs];

   uint64_t cur = remote_src;
   size_t total_read = 0;
   while (len > 0) {
     struct iovec dst_iov = {
         .iov_base = &reinterpret_cast<uint8_t*>(dst)[total_read], .iov_len = len,
     };

     size_t iovecs_used = 0;
     while (len > 0) {
       if (iovecs_used == kMaxIovecs) {
         break;
       }

       // struct iovec uses void* for iov_base.
       if (cur >= UINTPTR_MAX) {
         errno = EFAULT;
         return total_read;
       }

       src_iovs[iovecs_used].iov_base = reinterpret_cast<void*>(cur);

       uintptr_t misalignment = cur & (getpagesize() - 1);
       size_t iov_len = getpagesize() - misalignment;
       iov_len = std::min(iov_len, len);

       len -= iov_len;
       if (__builtin_add_overflow(cur, iov_len, &cur)) {
         errno = EFAULT;
         return total_read;
       }

       src_iovs[iovecs_used].iov_len = iov_len;
       ++iovecs_used;
     }

     ssize_t rc = process_vm_readv(pid, &dst_iov, 1, src_iovs, iovecs_used, 0);
     if (rc == -1) {
       return total_read;
     }
     total_read += rc;
   }
   return total_read;
 }

 static bool PtraceReadLong(pid_t pid, uint64_t addr, long* value) {
   // ptrace() returns -1 and sets errno when the operation fails.
   // To disambiguate -1 from a valid result, we clear errno beforehand.
   errno = 0;
   *value = ptrace(PTRACE_PEEKTEXT, pid, reinterpret_cast<void*>(addr), nullptr);
   if (*value == -1 && errno) {
     return false;
   }
   return true;
 }

 static size_t PtraceRead(pid_t pid, uint64_t addr, void* dst, size_t bytes) {
   // Make sure that there is no overflow.
   uint64_t max_size;
   if (__builtin_add_overflow(addr, bytes, &max_size)) {
     return 0;
   }

   size_t bytes_read = 0;
   long data;
   size_t align_bytes = addr & (sizeof(long) - 1);
   if (align_bytes != 0) {
     if (!PtraceReadLong(pid, addr & ~(sizeof(long) - 1), &data)) {
       return 0;
     }
     size_t copy_bytes = std::min(sizeof(long) - align_bytes, bytes);
     memcpy(dst, reinterpret_cast<uint8_t*>(&data) + align_bytes, copy_bytes);
     addr += copy_bytes;
     dst = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(dst) + copy_bytes);
     bytes -= copy_bytes;
     bytes_read += copy_bytes;
   }

   for (size_t i = 0; i < bytes / sizeof(long); i++) {
     if (!PtraceReadLong(pid, addr, &data)) {
       return bytes_read;
     }
     memcpy(dst, &data, sizeof(long));
     dst = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(dst) + sizeof(long));
     addr += sizeof(long);
     bytes_read += sizeof(long);
   }

   size_t left_over = bytes & (sizeof(long) - 1);
   if (left_over) {
     if (!PtraceReadLong(pid, addr, &data)) {
       return bytes_read;
     }
     memcpy(dst, &data, left_over);
     bytes_read += left_over;
   }
   return bytes_read;
 }

 bool Memory::ReadFully(uint64_t addr, void* dst, size_t size) {
   size_t rc = Read(addr, dst, size);
   return rc == size;
 }

 bool Memory::ReadString(uint64_t addr, std::string* string, uint64_t max_read) {
   string->clear();
   uint64_t bytes_read = 0;
   while (bytes_read < max_read) {
     uint8_t value;
     if (!ReadFully(addr, &value, sizeof(value))) {
       return false;
     }
     if (value == '\0') {
       return true;
     }
     string->push_back(value);
     addr++;
     bytes_read++;
   }
   return false;
 }

 std::unique_ptr<Memory> Memory::CreateFileMemory(const std::string& path, uint64_t offset) {
   auto memory = std::make_unique<MemoryFileAtOffset>();

   if (memory->Init(path, offset)) {
     return memory;
   }

   return nullptr;
 }

 std::shared_ptr<Memory> Memory::CreateProcessMemory(pid_t pid) {
   if (pid == getpid()) {
     return std::shared_ptr<Memory>(new MemoryLocal());
   }
   return std::shared_ptr<Memory>(new MemoryRemote(pid));
 }

 std::shared_ptr<Memory> Memory::CreateProcessMemoryCached(pid_t pid) {
   if (pid == getpid()) {
     return std::shared_ptr<Memory>(new MemoryCache(new MemoryLocal()));
   }
   return std::shared_ptr<Memory>(new MemoryCache(new MemoryRemote(pid)));
 }

 std::shared_ptr<Memory> Memory::CreateOfflineMemory(const uint8_t* data, uint64_t start,
                                                     uint64_t end) {
   return std::shared_ptr<Memory>(new MemoryOfflineBuffer(data, start, end));
 }

 size_t MemoryBuffer::Read(uint64_t addr, void* dst, size_t size) {
   if (addr >= raw_.size()) {
     return 0;
   }

   size_t bytes_left = raw_.size() - static_cast<size_t>(addr);
   const unsigned char* actual_base = static_cast<const unsigned char*>(raw_.data()) + addr;
   size_t actual_len = std::min(bytes_left, size);

   memcpy(dst, actual_base, actual_len);
   return actual_len;
 }

 uint8_t* MemoryBuffer::GetPtr(size_t offset) {
   if (offset < raw_.size()) {
     return &raw_[offset];
   }
   return nullptr;
 }

 MemoryFileAtOffset::~MemoryFileAtOffset() {
   Clear();
 }

 void MemoryFileAtOffset::Clear() {
   if (data_) {
     munmap(&data_[-offset_], size_ + offset_);
     data_ = nullptr;
   }
 }

 bool MemoryFileAtOffset::Init(const std::string& file, uint64_t offset, uint64_t size) {
   // Clear out any previous data if it exists.
   Clear();

   android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(file.c_str(), O_RDONLY | O_CLOEXEC)));
   if (fd == -1) {
     return false;
   }
   struct stat buf;
   if (fstat(fd, &buf) == -1) {
     return false;
   }
   if (offset >= static_cast<uint64_t>(buf.st_size)) {
     return false;
   }

   offset_ = offset & (getpagesize() - 1);
   uint64_t aligned_offset = offset & ~(getpagesize() - 1);
   if (aligned_offset > static_cast<uint64_t>(buf.st_size) ||
       offset > static_cast<uint64_t>(buf.st_size)) {
     return false;
   }

   size_ = buf.st_size - aligned_offset;
   uint64_t max_size;
   if (!__builtin_add_overflow(size, offset_, &max_size) && max_size < size_) {
     // Truncate the mapped size.
     size_ = max_size;
   }
   void* map = mmap(nullptr, size_, PROT_READ, MAP_PRIVATE, fd, aligned_offset);
   if (map == MAP_FAILED) {
     return false;
   }

   data_ = &reinterpret_cast<uint8_t*>(map)[offset_];
   size_ -= offset_;

   return true;
 }

 size_t MemoryFileAtOffset::Read(uint64_t addr, void* dst, size_t size) {
   if (addr >= size_) {
     return 0;
   }

   size_t bytes_left = size_ - static_cast<size_t>(addr);
   const unsigned char* actual_base = static_cast<const unsigned char*>(data_) + addr;
   size_t actual_len = std::min(bytes_left, size);

   memcpy(dst, actual_base, actual_len);
   return actual_len;
 }

 size_t MemoryRemote::Read(uint64_t addr, void* dst, size_t size) {
 #if !defined(__LP64__)
   // Cannot read an address greater than 32 bits in a 32 bit context.
   if (addr > UINT32_MAX) {
     return 0;
   }
 #endif

   size_t (*read_func)(pid_t, uint64_t, void*, size_t) =
       reinterpret_cast<size_t (*)(pid_t, uint64_t, void*, size_t)>(read_redirect_func_.load());
   if (read_func != nullptr) {
     return read_func(pid_, addr, dst, size);
   } else {
     // Prefer process_vm_read, try it first. If it doesn't work, use the
     // ptrace function. If at least one of them returns at least some data,
     // set that as the permanent function to use.
     // This assumes that if process_vm_read works once, it will continue
     // to work.
     size_t bytes = ProcessVmRead(pid_, addr, dst, size);
     if (bytes > 0) {
       read_redirect_func_ = reinterpret_cast<uintptr_t>(ProcessVmRead);
       return bytes;
     }
     bytes = PtraceRead(pid_, addr, dst, size);
     if (bytes > 0) {
       read_redirect_func_ = reinterpret_cast<uintptr_t>(PtraceRead);
     }
     return bytes;
   }
 }

 size_t MemoryLocal::Read(uint64_t addr, void* dst, size_t size) {
   return ProcessVmRead(getpid(), addr, dst, size);
 }

 MemoryRange::MemoryRange(const std::shared_ptr<Memory>& memory, uint64_t begin, uint64_t length,
                          uint64_t offset)
     : memory_(memory), begin_(begin), length_(length), offset_(offset) {}

 size_t MemoryRange::Read(uint64_t addr, void* dst, size_t size) {
   if (addr < offset_) {
     return 0;
   }

   uint64_t read_offset = addr - offset_;
   if (read_offset >= length_) {
     return 0;
   }

   uint64_t read_length = std::min(static_cast<uint64_t>(size), length_ - read_offset);
   uint64_t read_addr;
   if (__builtin_add_overflow(read_offset, begin_, &read_addr)) {
     return 0;
   }

   return memory_->Read(read_addr, dst, read_length);
 }

 void MemoryRanges::Insert(MemoryRange* memory) {
   maps_.emplace(memory->offset() + memory->length(), memory);
 }

 size_t MemoryRanges::Read(uint64_t addr, void* dst, size_t size) {
   auto entry = maps_.upper_bound(addr);
   if (entry != maps_.end()) {
     return entry->second->Read(addr, dst, size);
   }
   return 0;
 }

 bool MemoryOffline::Init(const std::string& file, uint64_t offset) {
   auto memory_file = std::make_shared<MemoryFileAtOffset>();
   if (!memory_file->Init(file, offset)) {
     return false;
   }

   // The first uint64_t value is the start of memory.
   uint64_t start;
   if (!memory_file->ReadFully(0, &start, sizeof(start))) {
     return false;
   }

   uint64_t size = memory_file->Size();
   if (__builtin_sub_overflow(size, sizeof(start), &size)) {
     return false;
   }

   memory_ = std::make_unique<MemoryRange>(memory_file, sizeof(start), size, start);
   return true;
 }

 size_t MemoryOffline::Read(uint64_t addr, void* dst, size_t size) {
   if (!memory_) {
     return 0;
   }

   return memory_->Read(addr, dst, size);
 }

 MemoryOfflineBuffer::MemoryOfflineBuffer(const uint8_t* data, uint64_t start, uint64_t end)
     : data_(data), start_(start), end_(end) {}

 void MemoryOfflineBuffer::Reset(const uint8_t* data, uint64_t start, uint64_t end) {
   data_ = data;
   start_ = start;
   end_ = end;
 }

 size_t MemoryOfflineBuffer::Read(uint64_t addr, void* dst, size_t size) {
   if (addr < start_ || addr >= end_) {
     return 0;
   }

   size_t read_length = std::min(size, static_cast<size_t>(end_ - addr));
   memcpy(dst, &data_[addr - start_], read_length);
   return read_length;
 }

 MemoryOfflineParts::~MemoryOfflineParts() {
   for (auto memory : memories_) {
     delete memory;
   }
 }

 size_t MemoryOfflineParts::Read(uint64_t addr, void* dst, size_t size) {
   if (memories_.empty()) {
     return 0;
   }

   // Do a read on each memory object, no support for reading across the
   // different memory objects.
   for (MemoryOffline* memory : memories_) {
     size_t bytes = memory->Read(addr, dst, size);
     if (bytes != 0) {
       return bytes;
     }
   }
   return 0;
 }

 size_t MemoryCache::Read(uint64_t addr, void* dst, size_t size) {
   // Only bother caching and looking at the cache if this is a small read for now.
   if (size > 64) {
     return impl_->Read(addr, dst, size);
   }

   uint64_t addr_page = addr >> kCacheBits;
   auto entry = cache_.find(addr_page);
   uint8_t* cache_dst;
   if (entry != cache_.end()) {
     cache_dst = entry->second;
   } else {
     cache_dst = cache_[addr_page];
     if (!impl_->ReadFully(addr_page << kCacheBits, cache_dst, kCacheSize)) {
       // Erase the entry.
       cache_.erase(addr_page);
       return impl_->Read(addr, dst, size);
     }
   }
   size_t max_read = ((addr_page + 1) << kCacheBits) - addr;
   if (size <= max_read) {
     memcpy(dst, &cache_dst[addr & kCacheMask], size);
     return size;
   }

   // The read crossed into another cached entry, since a read can only cross
   // into one extra cached page, duplicate the code rather than looping.
   memcpy(dst, &cache_dst[addr & kCacheMask], max_read);
   dst = &reinterpret_cast<uint8_t*>(dst)[max_read];
   addr_page++;

   entry = cache_.find(addr_page);
   if (entry != cache_.end()) {
     cache_dst = entry->second;
   } else {
     cache_dst = cache_[addr_page];
     if (!impl_->ReadFully(addr_page << kCacheBits, cache_dst, kCacheSize)) {
       // Erase the entry.
       cache_.erase(addr_page);
       return impl_->Read(addr_page << kCacheBits, dst, size - max_read) + max_read;
     }
   }
   memcpy(dst, cache_dst, size - max_read);
   return size;
 }

 }  // namespace unwindstack
	/*
	* 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 <errno.h>
	#include <fcntl.h>
	#include <string.h>
	#include <sys/mman.h>
	#include <sys/ptrace.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <sys/uio.h>
	#include <unistd.h>

	#include <algorithm>
	#include <memory>

	#include <android-base/unique_fd.h>

	#include <unwindstack/Memory.h>

	#include "Check.h"
	#include "MemoryBuffer.h"
	#include "MemoryCache.h"
	#include "MemoryFileAtOffset.h"
	#include "MemoryLocal.h"
	#include "MemoryOffline.h"
	#include "MemoryOfflineBuffer.h"
	#include "MemoryRange.h"
	#include "MemoryRemote.h"

	namespace unwindstack {

	static size_t ProcessVmRead(pid_t pid, uint64_t remote_src, void* dst, size_t len) {

	// Split up the remote read across page boundaries.
	// From the manpage:
	// A partial read/write may result if one of the remote_iov elements points to an invalid
	// memory region in the remote process.
	//
	// Partial transfers apply at the granularity of iovec elements. These system calls won't
	// perform a partial transfer that splits a single iovec element.
	constexpr size_t kMaxIovecs = 64;
	struct iovec src_iovs[kMaxIovecs];

	uint64_t cur = remote_src;
	size_t total_read = 0;
	while (len > 0) {
	struct iovec dst_iov = {
	.iov_base = &reinterpret_cast<uint8_t*>(dst)[total_read], .iov_len = len,
	};

	size_t iovecs_used = 0;
	while (len > 0) {
	if (iovecs_used == kMaxIovecs) {
	break;
	}

	// struct iovec uses void* for iov_base.
	if (cur >= UINTPTR_MAX) {
	errno = EFAULT;
	return total_read;
	}

	src_iovs[iovecs_used].iov_base = reinterpret_cast<void*>(cur);

	uintptr_t misalignment = cur & (getpagesize() - 1);
	size_t iov_len = getpagesize() - misalignment;
	iov_len = std::min(iov_len, len);

	len -= iov_len;
	if (__builtin_add_overflow(cur, iov_len, &cur)) {
	errno = EFAULT;
	return total_read;
	}

	src_iovs[iovecs_used].iov_len = iov_len;
	++iovecs_used;
	}

	ssize_t rc = process_vm_readv(pid, &dst_iov, 1, src_iovs, iovecs_used, 0);
	if (rc == -1) {
	return total_read;
	}
	total_read += rc;
	}
	return total_read;
	}

	static bool PtraceReadLong(pid_t pid, uint64_t addr, long* value) {
	// ptrace() returns -1 and sets errno when the operation fails.
	// To disambiguate -1 from a valid result, we clear errno beforehand.
	errno = 0;
	value = ptrace(PTRACE_PEEKTEXT, pid, reinterpret_cast<void>(addr), nullptr);
	if (*value == -1 && errno) {
	return false;
	}
	return true;
	}

	static size_t PtraceRead(pid_t pid, uint64_t addr, void* dst, size_t bytes) {
	// Make sure that there is no overflow.
	uint64_t max_size;
	if (__builtin_add_overflow(addr, bytes, &max_size)) {
	return 0;
	}

	size_t bytes_read = 0;
	long data;
	size_t align_bytes = addr & (sizeof(long) - 1);
	if (align_bytes != 0) {
	if (!PtraceReadLong(pid, addr & ~(sizeof(long) - 1), &data)) {
	return 0;
	}
	size_t copy_bytes = std::min(sizeof(long) - align_bytes, bytes);
	memcpy(dst, reinterpret_cast<uint8_t*>(&data) + align_bytes, copy_bytes);
	addr += copy_bytes;
	dst = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(dst) + copy_bytes);
	bytes -= copy_bytes;
	bytes_read += copy_bytes;
	}

	for (size_t i = 0; i < bytes / sizeof(long); i++) {
	if (!PtraceReadLong(pid, addr, &data)) {
	return bytes_read;
	}
	memcpy(dst, &data, sizeof(long));
	dst = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(dst) + sizeof(long));
	addr += sizeof(long);
	bytes_read += sizeof(long);
	}

	size_t left_over = bytes & (sizeof(long) - 1);
	if (left_over) {
	if (!PtraceReadLong(pid, addr, &data)) {
	return bytes_read;
	}
	memcpy(dst, &data, left_over);
	bytes_read += left_over;
	}
	return bytes_read;
	}

	bool Memory::ReadFully(uint64_t addr, void* dst, size_t size) {
	size_t rc = Read(addr, dst, size);
	return rc == size;
	}

	bool Memory::ReadString(uint64_t addr, std::string* string, uint64_t max_read) {
	string->clear();
	uint64_t bytes_read = 0;
	while (bytes_read < max_read) {
	uint8_t value;
	if (!ReadFully(addr, &value, sizeof(value))) {
	return false;
	}
	if (value == '\0') {
	return true;
	}
	string->push_back(value);
	addr++;
	bytes_read++;
	}
	return false;
	}

	std::unique_ptr<Memory> Memory::CreateFileMemory(const std::string& path, uint64_t offset) {
	auto memory = std::make_unique<MemoryFileAtOffset>();

	if (memory->Init(path, offset)) {
	return memory;
	}

	return nullptr;
	}

	std::shared_ptr<Memory> Memory::CreateProcessMemory(pid_t pid) {
	if (pid == getpid()) {
	return std::shared_ptr<Memory>(new MemoryLocal());
	}
	return std::shared_ptr<Memory>(new MemoryRemote(pid));
	}

	std::shared_ptr<Memory> Memory::CreateProcessMemoryCached(pid_t pid) {
	if (pid == getpid()) {
	return std::shared_ptr<Memory>(new MemoryCache(new MemoryLocal()));
	}
	return std::shared_ptr<Memory>(new MemoryCache(new MemoryRemote(pid)));
	}

	std::shared_ptr<Memory> Memory::CreateOfflineMemory(const uint8_t* data, uint64_t start,
	uint64_t end) {
	return std::shared_ptr<Memory>(new MemoryOfflineBuffer(data, start, end));
	}

	size_t MemoryBuffer::Read(uint64_t addr, void* dst, size_t size) {
	if (addr >= raw_.size()) {
	return 0;
	}

	size_t bytes_left = raw_.size() - static_cast<size_t>(addr);
	const unsigned char* actual_base = static_cast<const unsigned char*>(raw_.data()) + addr;
	size_t actual_len = std::min(bytes_left, size);

	memcpy(dst, actual_base, actual_len);
	return actual_len;
	}

	uint8_t* MemoryBuffer::GetPtr(size_t offset) {
	if (offset < raw_.size()) {
	return &raw_[offset];
	}
	return nullptr;
	}

	MemoryFileAtOffset::~MemoryFileAtOffset() {
	Clear();
	}

	void MemoryFileAtOffset::Clear() {
	if (data_) {
	munmap(&data_[-offset_], size_ + offset_);
	data_ = nullptr;
	}
	}

	bool MemoryFileAtOffset::Init(const std::string& file, uint64_t offset, uint64_t size) {
	// Clear out any previous data if it exists.
	Clear();

	android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(file.c_str(), O_RDONLY \| O_CLOEXEC)));
	if (fd == -1) {
	return false;
	}
	struct stat buf;
	if (fstat(fd, &buf) == -1) {
	return false;
	}
	if (offset >= static_cast<uint64_t>(buf.st_size)) {
	return false;
	}

	offset_ = offset & (getpagesize() - 1);
	uint64_t aligned_offset = offset & ~(getpagesize() - 1);
	if (aligned_offset > static_cast<uint64_t>(buf.st_size) \|\|
	offset > static_cast<uint64_t>(buf.st_size)) {
	return false;
	}

	size_ = buf.st_size - aligned_offset;
	uint64_t max_size;
	if (!__builtin_add_overflow(size, offset_, &max_size) && max_size < size_) {
	// Truncate the mapped size.
	size_ = max_size;
	}
	void* map = mmap(nullptr, size_, PROT_READ, MAP_PRIVATE, fd, aligned_offset);
	if (map == MAP_FAILED) {
	return false;
	}

	data_ = &reinterpret_cast<uint8_t*>(map)[offset_];
	size_ -= offset_;

	return true;
	}

	size_t MemoryFileAtOffset::Read(uint64_t addr, void* dst, size_t size) {
	if (addr >= size_) {
	return 0;
	}

	size_t bytes_left = size_ - static_cast<size_t>(addr);
	const unsigned char* actual_base = static_cast<const unsigned char*>(data_) + addr;
	size_t actual_len = std::min(bytes_left, size);

	memcpy(dst, actual_base, actual_len);
	return actual_len;
	}

	size_t MemoryRemote::Read(uint64_t addr, void* dst, size_t size) {
	#if !defined(__LP64__)
	// Cannot read an address greater than 32 bits in a 32 bit context.
	if (addr > UINT32_MAX) {
	return 0;
	}
	#endif

	size_t (read_func)(pid_t, uint64_t, void, size_t) =
	reinterpret_cast<size_t ()(pid_t, uint64_t, void, size_t)>(read_redirect_func_.load());
	if (read_func != nullptr) {
	return read_func(pid_, addr, dst, size);
	} else {
	// Prefer process_vm_read, try it first. If it doesn't work, use the
	// ptrace function. If at least one of them returns at least some data,
	// set that as the permanent function to use.
	// This assumes that if process_vm_read works once, it will continue
	// to work.
	size_t bytes = ProcessVmRead(pid_, addr, dst, size);
	if (bytes > 0) {
	read_redirect_func_ = reinterpret_cast<uintptr_t>(ProcessVmRead);
	return bytes;
	}
	bytes = PtraceRead(pid_, addr, dst, size);
	if (bytes > 0) {
	read_redirect_func_ = reinterpret_cast<uintptr_t>(PtraceRead);
	}
	return bytes;
	}
	}

	size_t MemoryLocal::Read(uint64_t addr, void* dst, size_t size) {
	return ProcessVmRead(getpid(), addr, dst, size);
	}

	MemoryRange::MemoryRange(const std::shared_ptr<Memory>& memory, uint64_t begin, uint64_t length,
	uint64_t offset)
	: memory_(memory), begin_(begin), length_(length), offset_(offset) {}

	size_t MemoryRange::Read(uint64_t addr, void* dst, size_t size) {
	if (addr < offset_) {
	return 0;
	}

	uint64_t read_offset = addr - offset_;
	if (read_offset >= length_) {
	return 0;
	}

	uint64_t read_length = std::min(static_cast<uint64_t>(size), length_ - read_offset);
	uint64_t read_addr;
	if (__builtin_add_overflow(read_offset, begin_, &read_addr)) {
	return 0;
	}

	return memory_->Read(read_addr, dst, read_length);
	}

	void MemoryRanges::Insert(MemoryRange* memory) {
	maps_.emplace(memory->offset() + memory->length(), memory);
	}

	size_t MemoryRanges::Read(uint64_t addr, void* dst, size_t size) {
	auto entry = maps_.upper_bound(addr);
	if (entry != maps_.end()) {
	return entry->second->Read(addr, dst, size);
	}
	return 0;
	}

	bool MemoryOffline::Init(const std::string& file, uint64_t offset) {
	auto memory_file = std::make_shared<MemoryFileAtOffset>();
	if (!memory_file->Init(file, offset)) {
	return false;
	}

	// The first uint64_t value is the start of memory.
	uint64_t start;
	if (!memory_file->ReadFully(0, &start, sizeof(start))) {
	return false;
	}

	uint64_t size = memory_file->Size();
	if (__builtin_sub_overflow(size, sizeof(start), &size)) {
	return false;
	}

	memory_ = std::make_unique<MemoryRange>(memory_file, sizeof(start), size, start);
	return true;
	}

	size_t MemoryOffline::Read(uint64_t addr, void* dst, size_t size) {
	if (!memory_) {
	return 0;
	}

	return memory_->Read(addr, dst, size);
	}

	MemoryOfflineBuffer::MemoryOfflineBuffer(const uint8_t* data, uint64_t start, uint64_t end)
	: data_(data), start_(start), end_(end) {}

	void MemoryOfflineBuffer::Reset(const uint8_t* data, uint64_t start, uint64_t end) {
	data_ = data;
	start_ = start;
	end_ = end;
	}

	size_t MemoryOfflineBuffer::Read(uint64_t addr, void* dst, size_t size) {
	if (addr < start_ \|\| addr >= end_) {
	return 0;
	}

	size_t read_length = std::min(size, static_cast<size_t>(end_ - addr));
	memcpy(dst, &data_[addr - start_], read_length);
	return read_length;
	}

	MemoryOfflineParts::~MemoryOfflineParts() {
	for (auto memory : memories_) {
	delete memory;
	}
	}

	size_t MemoryOfflineParts::Read(uint64_t addr, void* dst, size_t size) {
	if (memories_.empty()) {
	return 0;
	}

	// Do a read on each memory object, no support for reading across the
	// different memory objects.
	for (MemoryOffline* memory : memories_) {
	size_t bytes = memory->Read(addr, dst, size);
	if (bytes != 0) {
	return bytes;
	}
	}
	return 0;
	}

	size_t MemoryCache::Read(uint64_t addr, void* dst, size_t size) {
	// Only bother caching and looking at the cache if this is a small read for now.
	if (size > 64) {
	return impl_->Read(addr, dst, size);
	}

	uint64_t addr_page = addr >> kCacheBits;
	auto entry = cache_.find(addr_page);
	uint8_t* cache_dst;
	if (entry != cache_.end()) {
	cache_dst = entry->second;
	} else {
	cache_dst = cache_[addr_page];
	if (!impl_->ReadFully(addr_page << kCacheBits, cache_dst, kCacheSize)) {
	// Erase the entry.
	cache_.erase(addr_page);
	return impl_->Read(addr, dst, size);
	}
	}
	size_t max_read = ((addr_page + 1) << kCacheBits) - addr;
	if (size <= max_read) {
	memcpy(dst, &cache_dst[addr & kCacheMask], size);
	return size;
	}

	// The read crossed into another cached entry, since a read can only cross
	// into one extra cached page, duplicate the code rather than looping.
	memcpy(dst, &cache_dst[addr & kCacheMask], max_read);
	dst = &reinterpret_cast<uint8_t*>(dst)[max_read];
	addr_page++;

	entry = cache_.find(addr_page);
	if (entry != cache_.end()) {
	cache_dst = entry->second;
	} else {
	cache_dst = cache_[addr_page];
	if (!impl_->ReadFully(addr_page << kCacheBits, cache_dst, kCacheSize)) {
	// Erase the entry.
	cache_.erase(addr_page);
	return impl_->Read(addr_page << kCacheBits, dst, size - max_read) + max_read;
	}
	}
	memcpy(dst, cache_dst, size - max_read);
	return size;
	}

	} // namespace unwindstack