apk安装和优化原理
hmpd6104
8年前
来自： http://blog.csdn.net/jltxgcy/article/details/50550420
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apk安装的方式有：
1、开机启动时安装
2、通过adb install 或者在手机中点击apk，进行界面安装。
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开机启动后在system_server中调用PackageManagerService.main，随着调用的深入，循环对每个apk都调用scanPackageLI方法，这个函数提取apk的AndroidManifest.xml里面的内容放在PackagemanagerService中，并且安装了apk，还有优化了dex。
安装apk的代码：
int ret = mInstaller.install(pkgName, useEncryptedFSDir, pkg.applicationInfo.uid, pkg.applicationInfo.uid);
优化dex的代码：
if (performDexOptLI(pkg, forceDex) == DEX_OPT_FAILED) { mLastScanError = PackageManager.INSTALL_FAILED_DEXOPT; return null; }private int performDexOptLI(PackageParser.Package pkg, boolean forceDex) { boolean performed = false; if ((pkg.applicationInfo.flags&ApplicationInfo.FLAG_HAS_CODE) != 0 && mInstaller != null) { String path = pkg.mScanPath; int ret = 0; try { if (forceDex || dalvik.system.DexFile.isDexOptNeeded(path)) { ret = mInstaller.dexopt(path, pkg.applicationInfo.uid, !isForwardLocked(pkg)); pkg.mDidDexOpt = true; performed = true; } } catch (FileNotFoundException e) { Slog.w(TAG, "Apk not found for dexopt: " + path); ret = -1; } catch (IOException e) { Slog.w(TAG, "IOException reading apk: " + path, e); ret = -1; } catch (dalvik.system.StaleDexCacheError e) { Slog.w(TAG, "StaleDexCacheError when reading apk: " + path, e); ret = -1; } catch (Exception e) { Slog.w(TAG, "Exception when doing dexopt : ", e); ret = -1; } if (ret < 0) { //error from installer return DEX_OPT_FAILED; } } return performed ? DEX_OPT_PERFORMED : DEX_OPT_SKIPPED; } mInstaller.dexopt 通过socket通信 让installd 进程(由init进程起来了)执行do_dexopt-->dexopt-->fork出子进程去执行run_dexopt，安装和优化的调用流程请参考 Android安装服务installd源码分析。 run_dexopt代码如下：
static void run_dexopt(int zip_fd, int odex_fd, const char* input_file_name, const char* dexopt_flags) { //input_file_name为apk的路径 static const char* DEX_OPT_BIN = "/system/bin/dexopt"; static const int MAX_INT_LEN = 12; char zip_num[MAX_INT_LEN]; char odex_num[MAX_INT_LEN]; sprintf(zip_num, "%d", zip_fd);//apk文件句柄 sprintf(odex_num, "%d", odex_fd);//dex文件句柄 //调用/system/bin/dexopt工具来优化apk文件 execl(DEX_OPT_BIN, DEX_OPT_BIN, "--zip", zip_num, odex_num, input_file_name, dexopt_flags, (char*) NULL); ALOGE("execl(%s) failed: %s\n", DEX_OPT_BIN, strerror(errno)); } fork出的子线程执行的是/system/bin/dexopt，代码位于dalvik\dexopt\OptMain.c
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执行的是/system/bin/dexopt，实际上就是OptMain.c的main函数。
/* * Main entry point. Decide where to go. */ int main(int argc, char* const argv[]) { set_process_name("dexopt"); setvbuf(stdout, NULL, _IONBF, 0); if (argc > 1) { if (strcmp(argv[1], "--zip") == 0) return fromZip(argc, argv); else if (strcmp(argv[1], "--dex") == 0) return fromDex(argc, argv); else if (strcmp(argv[1], "--preopt") == 0) return preopt(argc, argv); } ...... return 1; } 代码位于 dalvik\dexopt\ OptMain.c。 由于执行时传入的参数是--zip，所以这里执行fromZip。
static int fromZip(int argc, char* const argv[]) { ...... result = processZipFile(zipFd, cacheFd, zipName, dexoptFlags); bail: return result; } 代码位于 dalvik\dexopt\ OptMain.c。 然后经过processZipFile->extractAndProcessZip->dvmContinueOptimization。
bool dvmContinueOptimization(int fd, off_t dexOffset, long dexLength, const char* fileName, u4 modWhen, u4 crc, bool isBootstrap) { DexClassLookup* pClassLookup = NULL; RegisterMapBuilder* pRegMapBuilder = NULL; u4 headerFlags = 0; ...... { /* * Map the entire file (so we don't have to worry about page * alignment). The expectation is that the output file contains * our DEX data plus room for a small header. */ bool success; void* mapAddr; mapAddr = mmap(NULL, dexOffset + dexLength, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (mapAddr == MAP_FAILED) { LOGE("unable to mmap DEX cache: %s\n", strerror(errno)); goto bail; } ...... success = rewriteDex(((u1*) mapAddr) + dexOffset, dexLength, &headerFlags, &pClassLookup); if (success) { DvmDex* pDvmDex = NULL; u1* dexAddr = ((u1*) mapAddr) + dexOffset; if (dvmDexFileOpenPartial(dexAddr, dexLength, &pDvmDex) != 0) { LOGE("Unable to create DexFile\n"); success = false; } else { ...... } } ...... if (!success) goto bail; } ...... if (writeDependencies(fd, modWhen, crc) != 0) { LOGW("Failed writing dependencies\n"); goto bail; } ...... if (!writeOptData(fd, pClassLookup, pRegMapBuilder)) { LOGW("Failed writing opt data\n"); goto bail; } ...... DexOptHeader optHdr; memset(&optHdr, 0xff, sizeof(optHdr)); memcpy(optHdr.magic, DEX_OPT_MAGIC, 4); memcpy(optHdr.magic+4, DEX_OPT_MAGIC_VERS, 4); optHdr.dexOffset = (u4) dexOffset; optHdr.dexLength = (u4) dexLength; optHdr.depsOffset = (u4) depsOffset; optHdr.depsLength = (u4) depsLength; optHdr.optOffset = (u4) optOffset; optHdr.optLength = (u4) optLength; optHdr.flags = headerFlags; optHdr.checksum = optChecksum; fsync(fd); /* ensure previous writes go before header is written */ lseek(fd, 0, SEEK_SET); if (sysWriteFully(fd, &optHdr, sizeof(optHdr), "DexOpt opt header") != 0) goto bail; LOGV("Successfully wrote DEX header\n"); result = true; //dvmRegisterMapDumpStats(); bail: dvmFreeRegisterMapBuilder(pRegMapBuilder); free(pClassLookup); return result; } 代码位于dalvik\vm\analysis\DexPrepare.c
dexOffset为odex文件头部大小，dexLength为dex文件长度。首先调用mmap把要优化的dex加载到内存虚拟地址mapAddr，这个dex其实就是位于/data/dalvik-cache/xxx@classes.dex。
然后调用rewriteDex函数对目标文件进行优化验证，其主要内容包括：字符顺序调整、字节码替换、字节码验证以及文件结构重新对齐。
然后通过writeDependencies写入依赖库信息，writeOptData写入其他优化信息，包括类索引信息以及寄存器映射关系。
最后修改odex文件的头部内容。
生成odex更为详细的流程请参考Android系统ODEX文件格式解析。
此时生成的odex其实就是位于/data/dalvik-cache/xxx@classes.dex。
odex结构图如下：
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adb install的安装流程请参考深入理解PackageManagerService。整个安装流程，首先把apk拷贝到/data/local/tmp目录下，在安装的过程中把apk拷贝到/data/app中，最后调用了PackageManagerService的InstallPackagtLI，这个函数调用了installNewPackageLI，installNewPackageLI调用了scanPackageLI，在这个函数里面完成了apk的优化和安装，优化和安装的流程和上面一样。
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本文中讲解了用于PathClassLoader加载/data/dalvik-cache/xxx@classes.dex的生成流程。
那么DexClassLoader加载apk的流程是什么呢？
注意PathClassLoader和DexClassLoader的构造函数有不同：
PathClassLoader：
public PathClassLoader(String path, String libPath, ClassLoader parent) { super(parent); if (path == null) throw new NullPointerException(); this.path = path; this.libPath = libPath; mPaths = path.split(":"); int length = mPaths.length; //System.out.println("PathClassLoader: " + mPaths); mFiles = new File[length]; mZips = new ZipFile[length]; mDexs = new DexFile[length]; boolean wantDex = System.getProperty("android.vm.dexfile", "").equals("true"); /* open all Zip and DEX files up front */ for (int i = 0; i < length; i++) { //System.out.println("My path is: " + mPaths[i]); File pathFile = new File(mPaths[i]); mFiles[i] = pathFile; if (pathFile.isFile()) { try { mZips[i] = new ZipFile(pathFile); } catch (IOException ioex) { // expecting IOException and ZipException //System.out.println("Failed opening '" + pathFile + "': " + ioex); //ioex.printStackTrace(); } if (wantDex) { /* we need both DEX and Zip, because dex has no resources */ try { mDexs[i] = new DexFile(pathFile); } catch (IOException ioex) {} } } } ...... }最终调用的是new DexFile(pathFile)。
而DexClassLoader：
public DexClassLoader(String dexPath, String dexOutputDir, String libPath, ClassLoader parent) { super(parent); if (dexPath == null || dexOutputDir == null) throw new NullPointerException(); mRawDexPath = dexPath; mDexOutputPath = dexOutputDir; mRawLibPath = libPath; String[] dexPathList = mRawDexPath.split(":"); int length = dexPathList.length; //System.out.println("DexClassLoader: " + dexPathList); mFiles = new File[length]; mZips = new ZipFile[length]; mDexs = new DexFile[length]; /* open all Zip and DEX files up front */ for (int i = 0; i < length; i++) { //System.out.println("My path is: " + dexPathList[i]); File pathFile = new File(dexPathList[i]); mFiles[i] = pathFile; if (pathFile.isFile()) { try { mZips[i] = new ZipFile(pathFile); } catch (IOException ioex) { // expecting IOException and ZipException System.out.println("Failed opening '" + pathFile + "': " + ioex); //ioex.printStackTrace(); } /* we need both DEX and Zip, because dex has no resources */ try { String outputName = generateOutputName(dexPathList[i], mDexOutputPath); mDexs[i] = DexFile.loadDex(dexPathList[i], outputName, 0); } catch (IOException ioex) { // might be a resource-only zip System.out.println("Failed loadDex '" + pathFile + "': " + ioex); } } else { if (VERBOSE_DEBUG) System.out.println("Not found: " + pathFile.getPath()); } } ....... } 最终调用的是DexFile.loadDex(dexPathList[i], outputName, 0)。 说明DexClassLoader还需要指定一个生成优化后的apk的路径。而PathClassLoader则不需要，因为在安装阶段已经生成了/data/dalvik-cache/xxx@classes.dex。