apk安裝和優化原理

hmpd6104 8年前發布 | 16K 次閱讀 Android開發移動開發

來自： http://blog.csdn.net/jltxgcy/article/details/50550420

0x00

apk安裝的方式有：

1、開機啟動時安裝

2、通過adb install 或者在手機中點擊apk，進行界面安裝。

0x01

開機啟動后在system_server中調用PackageManagerService.main，隨著調用的深入，循環對每個apk都調用scanPackageLI方法，這個函數提取apk的AndroidManifest.xml里面的內容放在PackagemanagerService中，并且安裝了apk，還有優化了dex。

安裝apk的代碼：

int ret = mInstaller.install(pkgName, useEncryptedFSDir, pkg.applicationInfo.uid,
                            pkg.applicationInfo.uid);

優化dex的代碼：

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 通過socket通信讓installd 進程(由init進程起來了)執行do_dexopt-->dexopt-->fork出子進程去執行run_dexopt，安裝和優化的調用流程請參考 Android安裝服務installd源碼分析。

run_dexopt代碼如下：

static void run_dexopt(int zip_fd, int odex_fd, const char* input_file_name,
    const char* dexopt_flags)
{
    //input_file_name為apk的路徑
    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
    //調用/system/bin/dexopt工具來優化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出的子線程執行的是/system/bin/dexopt，代碼位于dalvik\dexopt\OptMain.c

0x02

執行的是/system/bin/dexopt，實際上就是OptMain.c的main函數。

/*
 * 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;
}

代碼位于 dalvik\dexopt\ OptMain.c。

由于執行時傳入的參數是--zip，所以這里執行fromZip。

static int fromZip(int argc, char* const argv[])
{
    ......

    result = processZipFile(zipFd, cacheFd, zipName, dexoptFlags);

bail:
    return result;
}

代碼位于 dalvik\dexopt\ OptMain.c。
然后經過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;
}

代碼位于dalvik\vm\analysis\DexPrepare.c

dexOffset為odex文件頭部大小，dexLength為dex文件長度。首先調用mmap把要優化的dex加載到內存虛擬地址mapAddr，這個dex其實就是位于/data/dalvik-cache/xxx@classes.dex。

然后調用rewriteDex函數對目標文件進行優化驗證，其主要內容包括：字符順序調整、字節碼替換、字節碼驗證以及文件結構重新對齊。

然后通過writeDependencies寫入依賴庫信息，writeOptData寫入其他優化信息，包括類索引信息以及寄存器映射關系。

最后修改odex文件的頭部內容。

生成odex更為詳細的流程請參考Android系統ODEX文件格式解析。

此時生成的odex其實就是位于/data/dalvik-cache/xxx@classes.dex。

odex結構圖如下：

0x03

adb install的安裝流程請參考深入理解PackageManagerService。整個安裝流程，首先把apk拷貝到/data/local/tmp目錄下，在安裝的過程中把apk拷貝到/data/app中，最后調用了PackageManagerService的InstallPackagtLI，這個函數調用了installNewPackageLI，installNewPackageLI調用了scanPackageLI，在這個函數里面完成了apk的優化和安裝，優化和安裝的流程和上面一樣。

0x04

本文中講解了用于PathClassLoader加載/data/dalvik-cache/xxx@classes.dex的生成流程。

那么DexClassLoader加載apk的流程是什么呢？

注意PathClassLoader和DexClassLoader的構造函數有不同：

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) {}
                }
            }
        }
        ......
    }

最終調用的是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());
            }
        }

        .......
    }

最終調用的是DexFile.loadDex(dexPathList[i], outputName, 0)。

說明DexClassLoader還需要指定一個生成優化后的apk的路徑。而PathClassLoader則不需要，因為在安裝階段已經生成了/data/dalvik-cache/xxx@classes.dex。

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