src/dex_file.cc - platform/art - Git at Google

 // Copyright 2011 Google Inc. All Rights Reserved.

 #include "dex_file.h"

 #include <fcntl.h>
 #include <map>
 #include <stdio.h>
 #include <string.h>
 #include <sys/file.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <sys/types.h>

 #include "globals.h"
 #include "logging.h"
 #include "object.h"
 #include "os.h"
 #include "scoped_ptr.h"
 #include "stringprintf.h"
 #include "thread.h"
 #include "utils.h"
 #include "zip_archive.h"

 namespace art {

 const byte DexFile::kDexMagic[] = { 'd', 'e', 'x', '\n' };
 const byte DexFile::kDexMagicVersion[] = { '0', '3', '5', '\0' };

 DexFile::ClassPathEntry DexFile::FindInClassPath(const StringPiece& descriptor,
                                                  ClassPath& class_path) {
   for (size_t i = 0; i != class_path.size(); ++i) {
     const DexFile* dex_file = class_path[i];
     const DexFile::ClassDef* dex_class_def = dex_file->FindClassDef(descriptor);
     if (dex_class_def != NULL) {
       return ClassPathEntry(dex_file, dex_class_def);
     }
   }
   // TODO remove reinterpret_cast when issue with -std=gnu++0x host issue resolved
   return ClassPathEntry(reinterpret_cast<const DexFile*>(NULL),
                         reinterpret_cast<const DexFile::ClassDef*>(NULL));
 }

 DexFile::Closer::~Closer() {}

 DexFile::MmapCloser::MmapCloser(void* addr, size_t length) : addr_(addr), length_(length) {
   CHECK(addr != NULL);
 }
 DexFile::MmapCloser::~MmapCloser() {
   if (munmap(addr_, length_) == -1) {
     PLOG(INFO) << "munmap failed";
   }
 }

 DexFile::PtrCloser::PtrCloser(byte* addr) : addr_(addr) {}
 DexFile::PtrCloser::~PtrCloser() { delete[] addr_; }

 DexFile* DexFile::OpenFile(const std::string& filename) {
   int fd = open(filename.c_str(), O_RDONLY);  // TODO: scoped_fd
   if (fd == -1) {
     PLOG(ERROR) << "open(\"" << filename << "\", O_RDONLY) failed";
     return NULL;
   }
   struct stat sbuf;
   memset(&sbuf, 0, sizeof(sbuf));
   if (fstat(fd, &sbuf) == -1) {
     PLOG(ERROR) << "fstat \"" << filename << "\" failed";
     close(fd);
     return NULL;
   }
   size_t length = sbuf.st_size;
   void* addr = mmap(NULL, length, PROT_READ, MAP_SHARED, fd, 0);
   if (addr == MAP_FAILED) {
     PLOG(ERROR) << "mmap \"" << filename << "\" failed";
     close(fd);
     return NULL;
   }
   close(fd);
   byte* dex_file = reinterpret_cast<byte*>(addr);
   Closer* closer = new MmapCloser(addr, length);
   return Open(dex_file, length, closer);
 }

 static const char* kClassesDex = "classes.dex";

 class LockedFd {
  public:
    static LockedFd* CreateAndLock(std::string& name, mode_t mode) {
     int fd = open(name.c_str(), O_CREAT | O_RDWR, mode);
     if (fd == -1) {
       PLOG(ERROR) << "Can't open file '" << name << "'";
       return NULL;
     }
     fchmod(fd, mode);

     LOG(INFO) << "locking file " << name << " (fd=" << fd << ")";
     int result = flock(fd, LOCK_EX | LOCK_NB);
     if (result == -1) {
         LOG(WARNING) << "sleeping while locking file " << name;
         result = flock(fd, LOCK_EX);
     }
     if (result == -1 ) {
       PLOG(ERROR) << "Can't lock file '" << name << "'";
       close(fd);
       return NULL;
     }
     return new LockedFd(fd);
    }

    int GetFd() const {
      return fd_;
    }

   ~LockedFd() {
     if (fd_ != -1) {
       int result = flock(fd_, LOCK_UN);
       if (result == -1) {
         PLOG(WARNING) << "flock(" << fd_ << ", LOCK_UN) failed";
       }
       close(fd_);
     }
   }

  private:
   LockedFd(int fd) : fd_(fd) {}

   int fd_;
 };

 class TmpFile {
  public:
   TmpFile(const std::string name) : name_(name) {}
   ~TmpFile() {
     unlink(name_.c_str());
   }
  private:
   const std::string name_;
 };

 // Open classes.dex from within a .zip, .jar, .apk, ...
 DexFile* DexFile::OpenZip(const std::string& filename) {

   // First, look for a ".dex" alongside the jar file.  It will have
   // the same name/path except for the extension.

   // Example filename = dir/foo.jar
   std::string adjacent_dex_filename(filename);
   size_t found = adjacent_dex_filename.find_last_of(".");
   if (found == std::string::npos) {
     LOG(WARNING) << "No . in filename" << filename;
   }
   adjacent_dex_filename.replace(adjacent_dex_filename.begin() + found,
                                 adjacent_dex_filename.end(),
                                 ".dex");
   // Example adjacent_dex_filename = dir/foo.dex
   if (OS::FileExists(adjacent_dex_filename.c_str())) {
     DexFile* adjacent_dex_file = DexFile::OpenFile(adjacent_dex_filename);
     if (adjacent_dex_file != NULL) {
       // We don't verify anything in this case, because we aren't in
       // the cache and typically the file is in the readonly /system
       // area, so if something is wrong, there is nothing we can do.
       return adjacent_dex_file;
     }
     return NULL;
   }

   char resolved[PATH_MAX];
   char* absolute_path = realpath(filename.c_str(), resolved);
   if (absolute_path == NULL) {
       LOG(WARNING) << "Could not create absolute path for " << filename
                    << " when looking for classes.dex";
       return NULL;
   }
   std::string cache_file(absolute_path+1); // skip leading slash
   std::replace(cache_file.begin(), cache_file.end(), '/', '@');
   cache_file.push_back('@');
   cache_file.append(kClassesDex);
   // Example cache_file = parent@dir@foo.jar@classes.dex

   const char* data_root = getenv("ANDROID_DATA");
   if (data_root == NULL) {
       data_root = "/data";
   }

   std::string cache_path_tmp = StringPrintf("%s/art-cache/%s", data_root, cache_file.c_str());
   // Example cache_path_tmp = /data/art-cache/parent@dir@foo.jar@classes.dex

   scoped_ptr<ZipArchive> zip_archive(ZipArchive::Open(filename));
   if (zip_archive == NULL) {
     LOG(WARNING) << "Could not open " << filename << " when looking for classes.dex";
     return NULL;
   }
   scoped_ptr<ZipEntry> zip_entry(zip_archive->Find(kClassesDex));
   if (zip_entry == NULL) {
     LOG(WARNING) << "Could not find classes.dex within " << filename;
     return NULL;
   }

   std::string cache_path = StringPrintf("%s.%08x", cache_path_tmp.c_str(), zip_entry->GetCrc32());
   // Example cache_path = /data/art-cache/parent@dir@foo.jar@classes.dex.1a2b3c4d

   while (true) {
     if (OS::FileExists(cache_path.c_str())) {
       DexFile* cached_dex_file = DexFile::OpenFile(cache_path);
       if (cached_dex_file != NULL) {
         return cached_dex_file;
       }
     }

     // Try to open the temporary cache file, grabbing an exclusive
     // lock. If somebody else is working on it, we'll block here until
     // they complete.  Because we're waiting on an external resource,
     // we go into native mode.
     // Note that current_thread can be NULL if we're parsing the bootclasspath
     // during JNI_CreateJavaVM.
     Thread* current_thread = Thread::Current();
     Thread::State old;
     if (current_thread != NULL) {
         old = current_thread->GetState();
         current_thread->SetState(Thread::kNative);
     }
     scoped_ptr<LockedFd> fd(LockedFd::CreateAndLock(cache_path_tmp, 0644));
     if (current_thread != NULL) {
         current_thread->SetState(old);
     }
     if (fd == NULL) {
       return NULL;
     }

     // Check to see if the fd we opened and locked matches the file in
     // the filesystem.  If they don't, then somebody else unlinked
     // ours and created a new file, and we need to use that one
     // instead.  (If we caught them between the unlink and the create,
     // we'll get an ENOENT from the file stat.)
     struct stat fd_stat;
     int fd_stat_result = fstat(fd->GetFd(), &fd_stat);
     if (fd_stat_result == -1) {
       PLOG(ERROR) << "Can't stat open file '" << cache_path_tmp << "'";
       return NULL;
     }
     struct stat file_stat;
     int file_stat_result = stat(cache_path_tmp.c_str(), &file_stat);
     if (file_stat_result == -1 ||
         fd_stat.st_dev != file_stat.st_dev || fd_stat.st_ino != file_stat.st_ino) {
       LOG(WARNING) << "our open cache file is stale; sleeping and retrying";
       usleep(250 * 1000);  // if something is hosed, don't peg machine
       continue;
     }

     // We have the correct file open and locked. Extract classes.dex
     TmpFile tmp_file(cache_path_tmp);
     scoped_ptr<File> file(OS::FileFromFd(cache_path_tmp.c_str(), fd->GetFd()));
     if (file == NULL) {
       return NULL;
     }
     bool success = zip_entry->Extract(*file);
     if (!success) {
       return NULL;
     }

     // TODO restat and check length against zip_entry->GetUncompressedLength()?

     // Compute checksum and compare to zip. If things look okay, rename from tmp.
     off_t lseek_result = lseek(fd->GetFd(), 0, SEEK_SET);
     if (lseek_result == -1) {
       return NULL;
     }
     const size_t kBufSize = 32768;
     scoped_array<uint8_t> buf(new uint8_t[kBufSize]);
     if (buf == NULL) {
       return NULL;
     }
     uint32_t computed_crc = crc32(0L, Z_NULL, 0);
     while (true) {
       ssize_t bytes_read = TEMP_FAILURE_RETRY(read(fd->GetFd(), buf.get(), kBufSize));
       if (bytes_read == -1) {
         PLOG(ERROR) << "Problem computing CRC of '" << cache_path_tmp << "'";
         return NULL;
       }
       if (bytes_read == 0) {
         break;
       }
       computed_crc = crc32(computed_crc, buf.get(), bytes_read);
     }
     if (computed_crc != zip_entry->GetCrc32()) {
       return NULL;
     }
     int rename_result = rename(cache_path_tmp.c_str(), cache_path.c_str());
     if (rename_result == -1) {
       PLOG(ERROR) << "Can't install dex cache file '" << cache_path << "'"
                   << " from '" << cache_path_tmp << "'";
       unlink(cache_path.c_str());
     }
   }
   // NOTREACHED
 }

 DexFile* DexFile::OpenPtr(byte* ptr, size_t length) {
   CHECK(ptr != NULL);
   DexFile::Closer* closer = new PtrCloser(ptr);
   return Open(ptr, length, closer);
 }

 DexFile* DexFile::Open(const byte* dex_bytes, size_t length,
                        Closer* closer) {
   scoped_ptr<DexFile> dex_file(new DexFile(dex_bytes, length, closer));
   if (!dex_file->Init()) {
     return NULL;
   } else {
     return dex_file.release();
   }
 }

 DexFile::~DexFile() {}

 bool DexFile::Init() {
   InitMembers();
   if (!IsMagicValid()) {
     return false;
   }
   InitIndex();
   return true;
 }

 void DexFile::InitMembers() {
   const byte* b = base_;
   header_ = reinterpret_cast<const Header*>(b);
   const Header* h = header_;
   string_ids_ = reinterpret_cast<const StringId*>(b + h->string_ids_off_);
   type_ids_ = reinterpret_cast<const TypeId*>(b + h->type_ids_off_);
   field_ids_ = reinterpret_cast<const FieldId*>(b + h->field_ids_off_);
   method_ids_ = reinterpret_cast<const MethodId*>(b + h->method_ids_off_);
   proto_ids_ = reinterpret_cast<const ProtoId*>(b + h->proto_ids_off_);
   class_defs_ = reinterpret_cast<const ClassDef*>(b + h->class_defs_off_);
 }

 bool DexFile::IsMagicValid() {
   return CheckMagic(header_->magic_);
 }

 bool DexFile::CheckMagic(const byte* magic) {
   CHECK(magic != NULL);
   if (memcmp(magic, kDexMagic, sizeof(kDexMagic)) != 0) {
     LOG(WARNING) << "Unrecognized magic number:"
             << " " << magic[0]
             << " " << magic[1]
             << " " << magic[2]
             << " " << magic[3];
     return false;
   }
   const byte* version = &magic[sizeof(kDexMagic)];
   if (memcmp(version, kDexMagicVersion, sizeof(kDexMagicVersion)) != 0) {
     LOG(WARNING) << "Unrecognized version number:"
             << " " << version[0]
             << " " << version[1]
             << " " << version[2]
             << " " << version[3];
     return false;
   }
   return true;
 }

 void DexFile::InitIndex() {
   CHECK_EQ(index_.size(), 0U);
   for (size_t i = 0; i < NumClassDefs(); ++i) {
     const ClassDef& class_def = GetClassDef(i);
     const char* descriptor = GetClassDescriptor(class_def);
     index_[descriptor] = &class_def;
   }
 }

 const DexFile::ClassDef* DexFile::FindClassDef(const StringPiece& descriptor) const {
   CHECK(descriptor != NULL);
   Index::const_iterator it = index_.find(descriptor);
   if (it == index_.end()) {
     return NULL;
   } else {
     return it->second;
   }
 }

 // Materializes the method descriptor for a method prototype.  Method
 // descriptors are not stored directly in the dex file.  Instead, one
 // must assemble the descriptor from references in the prototype.
 char* DexFile::CreateMethodDescriptor(uint32_t proto_idx,
                                       int32_t* unicode_length) const {
   CHECK(unicode_length != NULL);
   const ProtoId& proto_id = GetProtoId(proto_idx);
   std::string descriptor;
   descriptor.push_back('(');
   const TypeList* type_list = GetProtoParameters(proto_id);
   size_t parameter_length = 0;
   if (type_list != NULL) {
     // A non-zero number of arguments.  Append the type names.
     for (size_t i = 0; i < type_list->Size(); ++i) {
       const TypeItem& type_item = type_list->GetTypeItem(i);
       uint32_t type_idx = type_item.type_idx_;
       int32_t type_length;
       const char* name = dexStringByTypeIdx(type_idx, &type_length);
       parameter_length += type_length;
       descriptor.append(name);
     }
   }
   descriptor.push_back(')');
   uint32_t return_type_idx = proto_id.return_type_idx_;
   int32_t return_type_length;
   const char* name = dexStringByTypeIdx(return_type_idx, &return_type_length);
   descriptor.append(name);
   // TODO: should this just return a std::string?
   scoped_ptr<char> c_string(new char[descriptor.size() + 1]);
   strcpy(c_string.get(), descriptor.c_str());
   *unicode_length = parameter_length + return_type_length + 2;  // 2 for ( and )
   return c_string.release();
 }

 // Read a signed integer.  "zwidth" is the zero-based byte count.
 static int32_t ReadSignedInt(const byte* ptr, int zwidth)
 {
   int32_t val = 0;
   for (int i = zwidth; i >= 0; --i) {
     val = ((uint32_t)val >> 8) | (((int32_t)*ptr++) << 24);
   }
   val >>= (3 - zwidth) * 8;
   return val;
 }

 // Read an unsigned integer.  "zwidth" is the zero-based byte count,
 // "fill_on_right" indicates which side we want to zero-fill from.
 static uint32_t ReadUnsignedInt(const byte* ptr, int zwidth,
                                 bool fill_on_right) {
   uint32_t val = 0;
   if (!fill_on_right) {
     for (int i = zwidth; i >= 0; --i) {
       val = (val >> 8) | (((uint32_t)*ptr++) << 24);
     }
     val >>= (3 - zwidth) * 8;
   } else {
     for (int i = zwidth; i >= 0; --i) {
       val = (val >> 8) | (((uint32_t)*ptr++) << 24);
     }
   }
   return val;
 }

 // Read a signed long.  "zwidth" is the zero-based byte count.
 static int64_t ReadSignedLong(const byte* ptr, int zwidth) {
   int64_t val = 0;
   for (int i = zwidth; i >= 0; --i) {
     val = ((uint64_t)val >> 8) | (((int64_t)*ptr++) << 56);
   }
   val >>= (7 - zwidth) * 8;
   return val;
 }

 // Read an unsigned long.  "zwidth" is the zero-based byte count,
 // "fill_on_right" indicates which side we want to zero-fill from.
 static uint64_t ReadUnsignedLong(const byte* ptr, int zwidth,
                                  bool fill_on_right) {
   uint64_t val = 0;
   if (!fill_on_right) {
     for (int i = zwidth; i >= 0; --i) {
       val = (val >> 8) | (((uint64_t)*ptr++) << 56);
     }
     val >>= (7 - zwidth) * 8;
   } else {
     for (int i = zwidth; i >= 0; --i) {
       val = (val >> 8) | (((uint64_t)*ptr++) << 56);
     }
   }
   return val;
 }

 DexFile::ValueType DexFile::ReadEncodedValue(const byte** stream,
                                              JValue* value) const {
   const byte* ptr = *stream;
   byte value_type = *ptr++;
   byte value_arg = value_type >> kEncodedValueArgShift;
   size_t width = value_arg + 1;  // assume and correct later
   int type = value_type & kEncodedValueTypeMask;
   switch (type) {
     case DexFile::kByte: {
       int32_t b = ReadSignedInt(ptr, value_arg);
       CHECK(IsInt(8, b));
       value->i = b;
       break;
     }
     case DexFile::kShort: {
       int32_t s = ReadSignedInt(ptr, value_arg);
       CHECK(IsInt(16, s));
       value->i = s;
       break;
     }
     case DexFile::kChar: {
       uint32_t c = ReadUnsignedInt(ptr, value_arg, false);
       CHECK(IsUint(16, c));
       value->i = c;
       break;
     }
     case DexFile::kInt:
       value->i = ReadSignedInt(ptr, value_arg);
       break;
     case DexFile::kLong:
       value->j = ReadSignedLong(ptr, value_arg);
       break;
     case DexFile::kFloat:
       value->i = ReadUnsignedInt(ptr, value_arg, true);
       break;
     case DexFile::kDouble:
       value->j = ReadUnsignedLong(ptr, value_arg, true);
       break;
     case DexFile::kBoolean:
       value->i = (value_arg != 0);
       width = 0;
       break;
     case DexFile::kString:
     case DexFile::kType:
     case DexFile::kMethod:
     case DexFile::kEnum:
       value->i = ReadUnsignedInt(ptr, value_arg, false);
       break;
     case DexFile::kField:
     case DexFile::kArray:
     case DexFile::kAnnotation:
       UNIMPLEMENTED(FATAL) << ": type " << type;
       break;
     case DexFile::kNull:
       value->i = 0;
       width = 0;
       break;
     default:
       LOG(FATAL) << "Unreached";
   }
   ptr += width;
   *stream = ptr;
   return static_cast<ValueType>(type);
 }

 }  // namespace art
	// Copyright 2011 Google Inc. All Rights Reserved.

	#include "dex_file.h"

	#include <fcntl.h>
	#include <map>
	#include <stdio.h>
	#include <string.h>
	#include <sys/file.h>
	#include <sys/mman.h>
	#include <sys/stat.h>
	#include <sys/types.h>

	#include "globals.h"
	#include "logging.h"
	#include "object.h"
	#include "os.h"
	#include "scoped_ptr.h"
	#include "stringprintf.h"
	#include "thread.h"
	#include "utils.h"
	#include "zip_archive.h"

	namespace art {

	const byte DexFile::kDexMagic[] = { 'd', 'e', 'x', '\n' };
	const byte DexFile::kDexMagicVersion[] = { '0', '3', '5', '\0' };

	DexFile::ClassPathEntry DexFile::FindInClassPath(const StringPiece& descriptor,
	ClassPath& class_path) {
	for (size_t i = 0; i != class_path.size(); ++i) {
	const DexFile* dex_file = class_path[i];
	const DexFile::ClassDef* dex_class_def = dex_file->FindClassDef(descriptor);
	if (dex_class_def != NULL) {
	return ClassPathEntry(dex_file, dex_class_def);
	}
	}
	// TODO remove reinterpret_cast when issue with -std=gnu++0x host issue resolved
	return ClassPathEntry(reinterpret_cast<const DexFile*>(NULL),
	reinterpret_cast<const DexFile::ClassDef*>(NULL));
	}

	DexFile::Closer::~Closer() {}

	DexFile::MmapCloser::MmapCloser(void* addr, size_t length) : addr_(addr), length_(length) {
	CHECK(addr != NULL);
	}
	DexFile::MmapCloser::~MmapCloser() {
	if (munmap(addr_, length_) == -1) {
	PLOG(INFO) << "munmap failed";
	}
	}

	DexFile::PtrCloser::PtrCloser(byte* addr) : addr_(addr) {}
	DexFile::PtrCloser::~PtrCloser() { delete[] addr_; }

	DexFile* DexFile::OpenFile(const std::string& filename) {
	int fd = open(filename.c_str(), O_RDONLY); // TODO: scoped_fd
	if (fd == -1) {
	PLOG(ERROR) << "open(\"" << filename << "\", O_RDONLY) failed";
	return NULL;
	}
	struct stat sbuf;
	memset(&sbuf, 0, sizeof(sbuf));
	if (fstat(fd, &sbuf) == -1) {
	PLOG(ERROR) << "fstat \"" << filename << "\" failed";
	close(fd);
	return NULL;
	}
	size_t length = sbuf.st_size;
	void* addr = mmap(NULL, length, PROT_READ, MAP_SHARED, fd, 0);
	if (addr == MAP_FAILED) {
	PLOG(ERROR) << "mmap \"" << filename << "\" failed";
	close(fd);
	return NULL;
	}
	close(fd);
	byte* dex_file = reinterpret_cast<byte*>(addr);
	Closer* closer = new MmapCloser(addr, length);
	return Open(dex_file, length, closer);
	}

	static const char* kClassesDex = "classes.dex";

	class LockedFd {
	public:
	static LockedFd* CreateAndLock(std::string& name, mode_t mode) {
	int fd = open(name.c_str(), O_CREAT \| O_RDWR, mode);
	if (fd == -1) {
	PLOG(ERROR) << "Can't open file '" << name << "'";
	return NULL;
	}
	fchmod(fd, mode);

	LOG(INFO) << "locking file " << name << " (fd=" << fd << ")";
	int result = flock(fd, LOCK_EX \| LOCK_NB);
	if (result == -1) {
	LOG(WARNING) << "sleeping while locking file " << name;
	result = flock(fd, LOCK_EX);
	}
	if (result == -1 ) {
	PLOG(ERROR) << "Can't lock file '" << name << "'";
	close(fd);
	return NULL;
	}
	return new LockedFd(fd);
	}

	int GetFd() const {
	return fd_;
	}

	~LockedFd() {
	if (fd_ != -1) {
	int result = flock(fd_, LOCK_UN);
	if (result == -1) {
	PLOG(WARNING) << "flock(" << fd_ << ", LOCK_UN) failed";
	}
	close(fd_);
	}
	}

	private:
	LockedFd(int fd) : fd_(fd) {}

	int fd_;
	};

	class TmpFile {
	public:
	TmpFile(const std::string name) : name_(name) {}
	~TmpFile() {
	unlink(name_.c_str());
	}
	private:
	const std::string name_;
	};

	// Open classes.dex from within a .zip, .jar, .apk, ...
	DexFile* DexFile::OpenZip(const std::string& filename) {

	// First, look for a ".dex" alongside the jar file. It will have
	// the same name/path except for the extension.

	// Example filename = dir/foo.jar
	std::string adjacent_dex_filename(filename);
	size_t found = adjacent_dex_filename.find_last_of(".");
	if (found == std::string::npos) {
	LOG(WARNING) << "No . in filename" << filename;
	}
	adjacent_dex_filename.replace(adjacent_dex_filename.begin() + found,
	adjacent_dex_filename.end(),
	".dex");
	// Example adjacent_dex_filename = dir/foo.dex
	if (OS::FileExists(adjacent_dex_filename.c_str())) {
	DexFile* adjacent_dex_file = DexFile::OpenFile(adjacent_dex_filename);
	if (adjacent_dex_file != NULL) {
	// We don't verify anything in this case, because we aren't in
	// the cache and typically the file is in the readonly /system
	// area, so if something is wrong, there is nothing we can do.
	return adjacent_dex_file;
	}
	return NULL;
	}

	char resolved[PATH_MAX];
	char* absolute_path = realpath(filename.c_str(), resolved);
	if (absolute_path == NULL) {
	LOG(WARNING) << "Could not create absolute path for " << filename
	<< " when looking for classes.dex";
	return NULL;
	}
	std::string cache_file(absolute_path+1); // skip leading slash
	std::replace(cache_file.begin(), cache_file.end(), '/', '@');
	cache_file.push_back('@');
	cache_file.append(kClassesDex);
	// Example cache_file = parent@dir@foo.jar@classes.dex

	const char* data_root = getenv("ANDROID_DATA");
	if (data_root == NULL) {
	data_root = "/data";
	}

	std::string cache_path_tmp = StringPrintf("%s/art-cache/%s", data_root, cache_file.c_str());
	// Example cache_path_tmp = /data/art-cache/parent@dir@foo.jar@classes.dex

	scoped_ptr<ZipArchive> zip_archive(ZipArchive::Open(filename));
	if (zip_archive == NULL) {
	LOG(WARNING) << "Could not open " << filename << " when looking for classes.dex";
	return NULL;
	}
	scoped_ptr<ZipEntry> zip_entry(zip_archive->Find(kClassesDex));
	if (zip_entry == NULL) {
	LOG(WARNING) << "Could not find classes.dex within " << filename;
	return NULL;
	}

	std::string cache_path = StringPrintf("%s.%08x", cache_path_tmp.c_str(), zip_entry->GetCrc32());
	// Example cache_path = /data/art-cache/parent@dir@foo.jar@classes.dex.1a2b3c4d

	while (true) {
	if (OS::FileExists(cache_path.c_str())) {
	DexFile* cached_dex_file = DexFile::OpenFile(cache_path);
	if (cached_dex_file != NULL) {
	return cached_dex_file;
	}
	}

	// Try to open the temporary cache file, grabbing an exclusive
	// lock. If somebody else is working on it, we'll block here until
	// they complete. Because we're waiting on an external resource,
	// we go into native mode.
	// Note that current_thread can be NULL if we're parsing the bootclasspath
	// during JNI_CreateJavaVM.
	Thread* current_thread = Thread::Current();
	Thread::State old;
	if (current_thread != NULL) {
	old = current_thread->GetState();
	current_thread->SetState(Thread::kNative);
	}
	scoped_ptr<LockedFd> fd(LockedFd::CreateAndLock(cache_path_tmp, 0644));
	if (current_thread != NULL) {
	current_thread->SetState(old);
	}
	if (fd == NULL) {
	return NULL;
	}

	// Check to see if the fd we opened and locked matches the file in
	// the filesystem. If they don't, then somebody else unlinked
	// ours and created a new file, and we need to use that one
	// instead. (If we caught them between the unlink and the create,
	// we'll get an ENOENT from the file stat.)
	struct stat fd_stat;
	int fd_stat_result = fstat(fd->GetFd(), &fd_stat);
	if (fd_stat_result == -1) {
	PLOG(ERROR) << "Can't stat open file '" << cache_path_tmp << "'";
	return NULL;
	}
	struct stat file_stat;
	int file_stat_result = stat(cache_path_tmp.c_str(), &file_stat);
	if (file_stat_result == -1 \|\|
	fd_stat.st_dev != file_stat.st_dev \|\| fd_stat.st_ino != file_stat.st_ino) {
	LOG(WARNING) << "our open cache file is stale; sleeping and retrying";
	usleep(250 * 1000); // if something is hosed, don't peg machine
	continue;
	}

	// We have the correct file open and locked. Extract classes.dex
	TmpFile tmp_file(cache_path_tmp);
	scoped_ptr<File> file(OS::FileFromFd(cache_path_tmp.c_str(), fd->GetFd()));
	if (file == NULL) {
	return NULL;
	}
	bool success = zip_entry->Extract(*file);
	if (!success) {
	return NULL;
	}

	// TODO restat and check length against zip_entry->GetUncompressedLength()?

	// Compute checksum and compare to zip. If things look okay, rename from tmp.
	off_t lseek_result = lseek(fd->GetFd(), 0, SEEK_SET);
	if (lseek_result == -1) {
	return NULL;
	}
	const size_t kBufSize = 32768;
	scoped_array<uint8_t> buf(new uint8_t[kBufSize]);
	if (buf == NULL) {
	return NULL;
	}
	uint32_t computed_crc = crc32(0L, Z_NULL, 0);
	while (true) {
	ssize_t bytes_read = TEMP_FAILURE_RETRY(read(fd->GetFd(), buf.get(), kBufSize));
	if (bytes_read == -1) {
	PLOG(ERROR) << "Problem computing CRC of '" << cache_path_tmp << "'";
	return NULL;
	}
	if (bytes_read == 0) {
	break;
	}
	computed_crc = crc32(computed_crc, buf.get(), bytes_read);
	}
	if (computed_crc != zip_entry->GetCrc32()) {
	return NULL;
	}
	int rename_result = rename(cache_path_tmp.c_str(), cache_path.c_str());
	if (rename_result == -1) {
	PLOG(ERROR) << "Can't install dex cache file '" << cache_path << "'"
	<< " from '" << cache_path_tmp << "'";
	unlink(cache_path.c_str());
	}
	}
	// NOTREACHED
	}

	DexFile* DexFile::OpenPtr(byte* ptr, size_t length) {
	CHECK(ptr != NULL);
	DexFile::Closer* closer = new PtrCloser(ptr);
	return Open(ptr, length, closer);
	}

	DexFile* DexFile::Open(const byte* dex_bytes, size_t length,
	Closer* closer) {
	scoped_ptr<DexFile> dex_file(new DexFile(dex_bytes, length, closer));
	if (!dex_file->Init()) {
	return NULL;
	} else {
	return dex_file.release();
	}
	}

	DexFile::~DexFile() {}

	bool DexFile::Init() {
	InitMembers();
	if (!IsMagicValid()) {
	return false;
	}
	InitIndex();
	return true;
	}

	void DexFile::InitMembers() {
	const byte* b = base_;
	header_ = reinterpret_cast<const Header*>(b);
	const Header* h = header_;
	string_ids_ = reinterpret_cast<const StringId*>(b + h->string_ids_off_);
	type_ids_ = reinterpret_cast<const TypeId*>(b + h->type_ids_off_);
	field_ids_ = reinterpret_cast<const FieldId*>(b + h->field_ids_off_);
	method_ids_ = reinterpret_cast<const MethodId*>(b + h->method_ids_off_);
	proto_ids_ = reinterpret_cast<const ProtoId*>(b + h->proto_ids_off_);
	class_defs_ = reinterpret_cast<const ClassDef*>(b + h->class_defs_off_);
	}

	bool DexFile::IsMagicValid() {
	return CheckMagic(header_->magic_);
	}

	bool DexFile::CheckMagic(const byte* magic) {
	CHECK(magic != NULL);
	if (memcmp(magic, kDexMagic, sizeof(kDexMagic)) != 0) {
	LOG(WARNING) << "Unrecognized magic number:"
	<< " " << magic[0]
	<< " " << magic[1]
	<< " " << magic[2]
	<< " " << magic[3];
	return false;
	}
	const byte* version = &magic[sizeof(kDexMagic)];
	if (memcmp(version, kDexMagicVersion, sizeof(kDexMagicVersion)) != 0) {
	LOG(WARNING) << "Unrecognized version number:"
	<< " " << version[0]
	<< " " << version[1]
	<< " " << version[2]
	<< " " << version[3];
	return false;
	}
	return true;
	}

	void DexFile::InitIndex() {
	CHECK_EQ(index_.size(), 0U);
	for (size_t i = 0; i < NumClassDefs(); ++i) {
	const ClassDef& class_def = GetClassDef(i);
	const char* descriptor = GetClassDescriptor(class_def);
	index_[descriptor] = &class_def;
	}
	}

	const DexFile::ClassDef* DexFile::FindClassDef(const StringPiece& descriptor) const {
	CHECK(descriptor != NULL);
	Index::const_iterator it = index_.find(descriptor);
	if (it == index_.end()) {
	return NULL;
	} else {
	return it->second;
	}
	}

	// Materializes the method descriptor for a method prototype. Method
	// descriptors are not stored directly in the dex file. Instead, one
	// must assemble the descriptor from references in the prototype.
	char* DexFile::CreateMethodDescriptor(uint32_t proto_idx,
	int32_t* unicode_length) const {
	CHECK(unicode_length != NULL);
	const ProtoId& proto_id = GetProtoId(proto_idx);
	std::string descriptor;
	descriptor.push_back('(');
	const TypeList* type_list = GetProtoParameters(proto_id);
	size_t parameter_length = 0;
	if (type_list != NULL) {
	// A non-zero number of arguments. Append the type names.
	for (size_t i = 0; i < type_list->Size(); ++i) {
	const TypeItem& type_item = type_list->GetTypeItem(i);
	uint32_t type_idx = type_item.type_idx_;
	int32_t type_length;
	const char* name = dexStringByTypeIdx(type_idx, &type_length);
	parameter_length += type_length;
	descriptor.append(name);
	}
	}
	descriptor.push_back(')');
	uint32_t return_type_idx = proto_id.return_type_idx_;
	int32_t return_type_length;
	const char* name = dexStringByTypeIdx(return_type_idx, &return_type_length);
	descriptor.append(name);
	// TODO: should this just return a std::string?
	scoped_ptr<char> c_string(new char[descriptor.size() + 1]);
	strcpy(c_string.get(), descriptor.c_str());
	*unicode_length = parameter_length + return_type_length + 2; // 2 for ( and )
	return c_string.release();
	}

	// Read a signed integer. "zwidth" is the zero-based byte count.
	static int32_t ReadSignedInt(const byte* ptr, int zwidth)
	{
	int32_t val = 0;
	for (int i = zwidth; i >= 0; --i) {
	val = ((uint32_t)val >> 8) \| (((int32_t)*ptr++) << 24);
	}
	val >>= (3 - zwidth) * 8;
	return val;
	}

	// Read an unsigned integer. "zwidth" is the zero-based byte count,
	// "fill_on_right" indicates which side we want to zero-fill from.
	static uint32_t ReadUnsignedInt(const byte* ptr, int zwidth,
	bool fill_on_right) {
	uint32_t val = 0;
	if (!fill_on_right) {
	for (int i = zwidth; i >= 0; --i) {
	val = (val >> 8) \| (((uint32_t)*ptr++) << 24);
	}
	val >>= (3 - zwidth) * 8;
	} else {
	for (int i = zwidth; i >= 0; --i) {
	val = (val >> 8) \| (((uint32_t)*ptr++) << 24);
	}
	}
	return val;
	}

	// Read a signed long. "zwidth" is the zero-based byte count.
	static int64_t ReadSignedLong(const byte* ptr, int zwidth) {
	int64_t val = 0;
	for (int i = zwidth; i >= 0; --i) {
	val = ((uint64_t)val >> 8) \| (((int64_t)*ptr++) << 56);
	}
	val >>= (7 - zwidth) * 8;
	return val;
	}

	// Read an unsigned long. "zwidth" is the zero-based byte count,
	// "fill_on_right" indicates which side we want to zero-fill from.
	static uint64_t ReadUnsignedLong(const byte* ptr, int zwidth,
	bool fill_on_right) {
	uint64_t val = 0;
	if (!fill_on_right) {
	for (int i = zwidth; i >= 0; --i) {
	val = (val >> 8) \| (((uint64_t)*ptr++) << 56);
	}
	val >>= (7 - zwidth) * 8;
	} else {
	for (int i = zwidth; i >= 0; --i) {
	val = (val >> 8) \| (((uint64_t)*ptr++) << 56);
	}
	}
	return val;
	}

	DexFile::ValueType DexFile::ReadEncodedValue(const byte** stream,
	JValue* value) const {
	const byte* ptr = *stream;
	byte value_type = *ptr++;
	byte value_arg = value_type >> kEncodedValueArgShift;
	size_t width = value_arg + 1; // assume and correct later
	int type = value_type & kEncodedValueTypeMask;
	switch (type) {
	case DexFile::kByte: {
	int32_t b = ReadSignedInt(ptr, value_arg);
	CHECK(IsInt(8, b));
	value->i = b;
	break;
	}
	case DexFile::kShort: {
	int32_t s = ReadSignedInt(ptr, value_arg);
	CHECK(IsInt(16, s));
	value->i = s;
	break;
	}
	case DexFile::kChar: {
	uint32_t c = ReadUnsignedInt(ptr, value_arg, false);
	CHECK(IsUint(16, c));
	value->i = c;
	break;
	}
	case DexFile::kInt:
	value->i = ReadSignedInt(ptr, value_arg);
	break;
	case DexFile::kLong:
	value->j = ReadSignedLong(ptr, value_arg);
	break;
	case DexFile::kFloat:
	value->i = ReadUnsignedInt(ptr, value_arg, true);
	break;
	case DexFile::kDouble:
	value->j = ReadUnsignedLong(ptr, value_arg, true);
	break;
	case DexFile::kBoolean:
	value->i = (value_arg != 0);
	width = 0;
	break;
	case DexFile::kString:
	case DexFile::kType:
	case DexFile::kMethod:
	case DexFile::kEnum:
	value->i = ReadUnsignedInt(ptr, value_arg, false);
	break;
	case DexFile::kField:
	case DexFile::kArray:
	case DexFile::kAnnotation:
	UNIMPLEMENTED(FATAL) << ": type " << type;
	break;
	case DexFile::kNull:
	value->i = 0;
	width = 0;
	break;
	default:
	LOG(FATAL) << "Unreached";
	}
	ptr += width;
	*stream = ptr;
	return static_cast<ValueType>(type);
	}

	} // namespace art