安裝APK時SO庫的選擇策略

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0X0 前言

在Android系統中，當咱們安裝apk文件的時候，lib目錄下的so文件會被解壓到app的原生庫目錄，通常來講是放到/data/data/<package-name>/lib目錄下，而根據系統和CPU架構的不一樣，其拷貝策略也是不同的，在咱們測試過程當中發現不正確地配置了so文件,好比某些app使用第三方的so時，只配置了其中某一種CPU架構的so，可能會形成app在某些機型上的適配問題。因此這篇文章主要介紹一下在不一樣版本的Android系統中，安裝apk時，PackageManagerService選擇解壓so庫的策略，並給出一些so文件配置的建議。

0x1 Android4.0之前

當apk被安裝時，執行路徑雖然有差異，但最終要調用到的一個核心函數是copyApk,負責拷貝apk中的資源。

參考2.3.6的android源碼，它的copyApk其內部函數一段選取原生庫so邏輯：

public static int listPackageNativeBinariesLI(ZipFile zipFile,
            List> nativeFiles) throws ZipException, IOException {
        String cpuAbi = Build.CPU_ABI;        int result = listPackageSharedLibsForAbiLI(zipFile, cpuAbi, nativeFiles);        /*
         * Some architectures are capable of supporting several CPU ABIs
         * for example, 'armeabi-v7a' also supports 'armeabi' native code
         * this is indicated by the definition of the ro.product.cpu.abi2
         * system property.
         *
         * only scan the package twice in case of ABI mismatch
         */
        if (result == PACKAGE_INSTALL_NATIVE_ABI_MISMATCH) {            final String cpuAbi2 = SystemProperties.get("ro.product.cpu.abi2", null);            if (cpuAbi2 != null) {
                result = listPackageSharedLibsForAbiLI(zipFile, cpuAbi2, nativeFiles);
            }            if (result == PACKAGE_INSTALL_NATIVE_ABI_MISMATCH) {
                Slog.w(TAG, "Native ABI mismatch from package file");                return PackageManager.INSTALL_FAILED_INVALID_APK;
            }            if (result == PACKAGE_INSTALL_NATIVE_FOUND_LIBRARIES) {
                cpuAbi = cpuAbi2;
            }
        }        /*
         * Debuggable packages may have gdbserver embedded, so add it to
         * the list to the list of items to be extracted (as lib/gdbserver)
         * into the application's native library directory later. */ if (result == PACKAGE_INSTALL_NATIVE_FOUND_LIBRARIES) { listPackageGdbServerLI(zipFile, cpuAbi, nativeFiles); } return PackageManager.INSTALL_SUCCEEDED; }複製代碼

這段代碼中的Build.CPU_ABI和「ro.product.cpu.abi2」分別爲手機支持的主abi和次abi屬性字符串，abi爲手機支持的指令集所表明的字符串，好比armeabi-v7a、armeabi、x8六、mips等，而主abi和次abi分別表示手機支持的第一指令集和第二指令集。代碼首先調用listPackageSharedLibsForAbiLI來遍歷主abi目錄。當主abi目錄不存在時，纔會接着調用listPackageSharedLibsForAbiLI遍歷次abi目錄。

/*
     * Find all files of the form lib//lib.so in the .apk
     * and add them to a list to be installed later.
     *
     * NOTE: this method may throw an IOException if the library cannot
     * be copied to its final destination, e.g. if there isn't enough * room left on the data partition, or a ZipException if the package * file is malformed. */ private static int listPackageSharedLibsForAbiLI(ZipFile zipFile, String cpuAbi, List> libEntries) throws IOException, ZipException { final int cpuAbiLen = cpuAbi.length(); boolean hasNativeLibraries = false; boolean installedNativeLibraries = false; if (DEBUG_NATIVE) { Slog.d(TAG, "Checking " + zipFile.getName() + " for shared libraries of CPU ABI type " + cpuAbi); } Enumeration entries = zipFile.entries(); while (entries.hasMoreElements()) { ZipEntry entry = entries.nextElement(); // skip directories if (entry.isDirectory()) { continue; } String entryName = entry.getName(); /* * Check that the entry looks like lib//lib.so * here, but don't check the ABI just yet.
             *
             * - must be sufficiently long
             * - must end with LIB_SUFFIX, i.e. ".so"
             * - must start with APK_LIB, i.e. "lib/"
             */
            if (entryName.length() < MIN_ENTRY_LENGTH || !entryName.endsWith(LIB_SUFFIX)
                    || !entryName.startsWith(APK_LIB)) {                continue;
            }            // file name must start with LIB_PREFIX, i.e. "lib"
            int lastSlash = entryName.lastIndexOf('/');            if (lastSlash < 0
                    || !entryName.regionMatches(lastSlash + 1, LIB_PREFIX, 0, LIB_PREFIX_LENGTH)) {                continue;
            }
            hasNativeLibraries = true;            // check the cpuAbi now, between lib/ and /lib.so
            if (lastSlash != APK_LIB_LENGTH + cpuAbiLen
                    || !entryName.regionMatches(APK_LIB_LENGTH, cpuAbi, 0, cpuAbiLen))                continue;            /*
             * Extract the library file name, ensure it doesn't contain * weird characters. we're guaranteed here that it doesn't contain * a directory separator though. */ String libFileName = entryName.substring(lastSlash+1); if (!FileUtils.isFilenameSafe(new File(libFileName))) { continue; } installedNativeLibraries = true; if (DEBUG_NATIVE) { Log.d(TAG, "Caching shared lib " + entry.getName()); } libEntries.add(Pair.create(entry, libFileName)); } if (!hasNativeLibraries) return PACKAGE_INSTALL_NATIVE_NO_LIBRARIES; if (!installedNativeLibraries) return PACKAGE_INSTALL_NATIVE_ABI_MISMATCH; return PACKAGE_INSTALL_NATIVE_FOUND_LIBRARIES; }複製代碼

listPackageSharedLibsForAbiLI中判斷當前遍歷的apk中文件的entry名是否符合so命名的規範且包含相應abi字符串名。若是符合則規則則將so的entry名加入list，若是遍歷失敗或者規則不匹配則返回相應錯誤碼。

拷貝so策略：

遍歷apk中文件，當apk中lib目錄下主abi子目錄中有so文件存在時，則所有拷貝主abi子目錄下的so；只有當主abi子目錄下沒有so文件的時候即PACKAGE_INSTALL_NATIVE_ABI_MISMATCH的狀況，纔會拷貝次ABI子目錄下的so文件。

策略問題：

當so放置不當時，安裝apk時會致使拷貝不全。好比apk的lib目錄下存在armeabi/libx.so,armeabi/liby.so,armeabi-v7a/libx.so這3個so文件,那麼在主ABI爲armeabi-v7a且系統版本小於4.0的手機上，apk安裝後，按照拷貝策略，只會拷貝主abi目錄下的文件即armeabi-v7a/libx.so，當加載liby.so時就會報找不到so的異常。另外若是主abi目錄不存在，這個策略會遍歷2次apk，效率偏低。

0x2 Android 4.0-Android 4.0.3

參考4.0.3的android源碼，同理，找處處理so拷貝的核心邏輯（native層）：

static install_status_titerateOverNativeFiles(JNIEnv *env, jstring javaFilePath, jstring javaCpuAbi, jstring javaCpuAbi2,
        iterFunc callFunc, void* callArg) {    ScopedUtfChars filePath(env, javaFilePath);    ScopedUtfChars cpuAbi(env, javaCpuAbi);    ScopedUtfChars cpuAbi2(env, javaCpuAbi2);
    ZipFileRO zipFile;    if (zipFile.open(filePath.c_str()) != NO_ERROR) {
        LOGI("Couldn't open APK %s\n", filePath.c_str());        return INSTALL_FAILED_INVALID_APK;
    }    const int N = zipFile.getNumEntries();    char fileName[PATH_MAX];    for (int i = 0; i < N; i++) {        const ZipEntryRO entry = zipFile.findEntryByIndex(i);        if (entry == NULL) {            continue;
        }        // Make sure this entry has a filename.
        if (zipFile.getEntryFileName(entry, fileName, sizeof(fileName))) {            continue;
        }        // Make sure we're in the lib directory of the ZIP. if (strncmp(fileName, APK_LIB, APK_LIB_LEN)) { continue; } // Make sure the filename is at least to the minimum library name size. const size_t fileNameLen = strlen(fileName); static const size_t minLength = APK_LIB_LEN + 2 + LIB_PREFIX_LEN + 1 + LIB_SUFFIX_LEN; if (fileNameLen < minLength) { continue; } const char* lastSlash = strrchr(fileName, '/'); LOG_ASSERT(lastSlash != NULL, "last slash was null somehow for %s\n", fileName); // Check to make sure the CPU ABI of this file is one we support. const char* cpuAbiOffset = fileName + APK_LIB_LEN; const size_t cpuAbiRegionSize = lastSlash - cpuAbiOffset; LOGV("Comparing ABIs %s and %s versus %s\n", cpuAbi.c_str(), cpuAbi2.c_str(), cpuAbiOffset); if (cpuAbi.size() == cpuAbiRegionSize && *(cpuAbiOffset + cpuAbi.size()) == '/' && !strncmp(cpuAbiOffset, cpuAbi.c_str(), cpuAbiRegionSize)) { LOGV("Using ABI %s\n", cpuAbi.c_str()); } else if (cpuAbi2.size() == cpuAbiRegionSize && *(cpuAbiOffset + cpuAbi2.size()) == '/' && !strncmp(cpuAbiOffset, cpuAbi2.c_str(), cpuAbiRegionSize)) { LOGV("Using ABI %s\n", cpuAbi2.c_str()); } else { LOGV("abi didn't match anything: %s (end at %zd)\n", cpuAbiOffset, cpuAbiRegionSize); continue; } // If this is a .so file, check to see if we need to copy it. if ((!strncmp(fileName + fileNameLen - LIB_SUFFIX_LEN, LIB_SUFFIX, LIB_SUFFIX_LEN) && !strncmp(lastSlash, LIB_PREFIX, LIB_PREFIX_LEN) && isFilenameSafe(lastSlash + 1)) || !strncmp(lastSlash + 1, GDBSERVER, GDBSERVER_LEN)) { install_status_t ret = callFunc(env, callArg, &zipFile, entry, lastSlash + 1); if (ret != INSTALL_SUCCEEDED) { LOGV("Failure for entry %s", lastSlash + 1); return ret; } } } return INSTALL_SUCCEEDED; }複製代碼

拷貝so策略：

遍歷apk中全部文件，若是符合so文件的規則，且爲主ABI目錄或者次ABI目錄下的so，就解壓拷貝到相應目錄。

策略問題：

存在同名so覆蓋，好比一個app的armeabi和armeabi-v7a目錄下都包含同名的so，那麼就會發生覆蓋現象，覆蓋的前後順序根據so文件對應ZipFileR0中的hash值而定，考慮這樣一個例子，假設一個apk同時有armeabi/libx.so和armeabi-v7a/libx.so，安裝到主ABI爲armeabi-v7a的手機上，拷貝so時根據遍歷順序，存在一種可能即armeab-v7a/libx.so優先遍歷並被拷貝，隨後armeabi/libx.so被遍歷拷貝，覆蓋了前者。原本應該加載armeabi-v7a目錄下的so，結果按照這個策略拷貝了armeabi目錄下的so。

apk中文件entry的散列計算函數以下：

/*
 * Simple string hash function for non-null-terminated strings.
 *//*static*/ unsigned int ZipFileRO::computeHash(const char* str, int len)
{
    unsigned int hash = 0;    while (len--)
        hash = hash * 31 + *str++;    return hash;
}/*
 * Add a new entry to the hash table.
 */void ZipFileRO::addToHash(const char* str, int strLen, unsigned int hash)
{    int ent = hash & (mHashTableSize-1);    /*
     * We over-allocate the table, so we're guaranteed to find an empty slot. */ while (mHashTable[ent].name != NULL) ent = (ent + 1) & (mHashTableSize-1); mHashTable[ent].name = str; mHashTable[ent].nameLen = strLen; }複製代碼

0x3 Android 4.0.4之後

以4.1.2系統爲例，遍歷選擇so邏輯以下：

static install_status_titerateOverNativeFiles(JNIEnv *env, jstring javaFilePath, jstring javaCpuAbi, jstring javaCpuAbi2,
        iterFunc callFunc, void* callArg) {    ScopedUtfChars filePath(env, javaFilePath);    ScopedUtfChars cpuAbi(env, javaCpuAbi);    ScopedUtfChars cpuAbi2(env, javaCpuAbi2);
    ZipFileRO zipFile;    if (zipFile.open(filePath.c_str()) != NO_ERROR) {
        ALOGI("Couldn't open APK %s\n", filePath.c_str());        return INSTALL_FAILED_INVALID_APK;
    }    const int N = zipFile.getNumEntries();    char fileName[PATH_MAX];
    bool hasPrimaryAbi = false;    for (int i = 0; i < N; i++) {        const ZipEntryRO entry = zipFile.findEntryByIndex(i);        if (entry == NULL) {            continue;
        }        // Make sure this entry has a filename.
        if (zipFile.getEntryFileName(entry, fileName, sizeof(fileName))) {            continue;
        }        // Make sure we're in the lib directory of the ZIP. if (strncmp(fileName, APK_LIB, APK_LIB_LEN)) { continue; } // Make sure the filename is at least to the minimum library name size. const size_t fileNameLen = strlen(fileName); static const size_t minLength = APK_LIB_LEN + 2 + LIB_PREFIX_LEN + 1 + LIB_SUFFIX_LEN; if (fileNameLen < minLength) { continue; } const char* lastSlash = strrchr(fileName, '/'); ALOG_ASSERT(lastSlash != NULL, "last slash was null somehow for %s\n", fileName); // Check to make sure the CPU ABI of this file is one we support. const char* cpuAbiOffset = fileName + APK_LIB_LEN; const size_t cpuAbiRegionSize = lastSlash - cpuAbiOffset; ALOGV("Comparing ABIs %s and %s versus %s\n", cpuAbi.c_str(), cpuAbi2.c_str(), cpuAbiOffset); if (cpuAbi.size() == cpuAbiRegionSize && *(cpuAbiOffset + cpuAbi.size()) == '/' && !strncmp(cpuAbiOffset, cpuAbi.c_str(), cpuAbiRegionSize)) { ALOGV("Using primary ABI %s\n", cpuAbi.c_str()); hasPrimaryAbi = true; } else if (cpuAbi2.size() == cpuAbiRegionSize && *(cpuAbiOffset + cpuAbi2.size()) == '/' && !strncmp(cpuAbiOffset, cpuAbi2.c_str(), cpuAbiRegionSize)) { /* * If this library matches both the primary and secondary ABIs, * only use the primary ABI. */ if (hasPrimaryAbi) { ALOGV("Already saw primary ABI, skipping secondary ABI %s\n", cpuAbi2.c_str()); continue; } else { ALOGV("Using secondary ABI %s\n", cpuAbi2.c_str()); } } else { ALOGV("abi didn't match anything: %s (end at %zd)\n", cpuAbiOffset, cpuAbiRegionSize); continue; } // If this is a .so file, check to see if we need to copy it. if ((!strncmp(fileName + fileNameLen - LIB_SUFFIX_LEN, LIB_SUFFIX, LIB_SUFFIX_LEN) && !strncmp(lastSlash, LIB_PREFIX, LIB_PREFIX_LEN) && isFilenameSafe(lastSlash + 1)) || !strncmp(lastSlash + 1, GDBSERVER, GDBSERVER_LEN)) { install_status_t ret = callFunc(env, callArg, &zipFile, entry, lastSlash + 1); if (ret != INSTALL_SUCCEEDED) { ALOGV("Failure for entry %s", lastSlash + 1); return ret; } } } return INSTALL_SUCCEEDED; }複製代碼

拷貝so策略：

遍歷apk中文件，當遍歷到有主Abi目錄的so時，拷貝並設置標記hasPrimaryAbi爲真，之後遍歷則只拷貝主Abi目錄下的so，當標記爲假的時候，若是遍歷的so的entry名包含次abi字符串，則拷貝該so。

策略問題：

通過實際測試，so放置不當時，安裝apk時存在so拷貝不全的狀況。這個策略想解決的問題是在4.0~4.0.3系統中的so隨意覆蓋的問題，即若是有主abi目錄的so則拷貝，若是主abi目錄不存在這個so則拷貝次abi目錄的so，但代碼邏輯是根據ZipFileR0的遍歷順序來決定是否拷貝so，假設存在這樣的apk，lib目錄下存在armeabi/libx.so,armeabi/liby.so,armeabi-v7a/libx.so這三個so文件，且hash的順序爲armeabi-v7a/libx.so在armeabi/liby.so以前，則apk安裝的時候liby.so根本不會被拷貝，由於按照拷貝策略，armeabi-v7a/libx.so會優先遍歷到，因爲它是主abi目錄的so文件，因此標記被設置了，當遍歷到armeabi/liby.so時，因爲標記被設置爲真，liby.so的拷貝就被忽略了,從而在加載liby.so的時候會報異常。

0x4 64位系統支持

Android在5.0以後支持64位ABI，以5.1.0系統爲例：

public static int copyNativeBinariesWithOverride(Handle handle, File libraryRoot,
            String abiOverride) {        try {            if (handle.multiArch) {                // Warn if we've set an abiOverride for multi-lib packages.. // By definition, we need to copy both 32 and 64 bit libraries for // such packages. if (abiOverride != null && !CLEAR_ABI_OVERRIDE.equals(abiOverride)) { Slog.w(TAG, "Ignoring abiOverride for multi arch application."); } int copyRet = PackageManager.NO_NATIVE_LIBRARIES; if (Build.SUPPORTED_32_BIT_ABIS.length > 0) { copyRet = copyNativeBinariesForSupportedAbi(handle, libraryRoot, Build.SUPPORTED_32_BIT_ABIS, true /* use isa specific subdirs */); if (copyRet < 0 && copyRet != PackageManager.NO_NATIVE_LIBRARIES && copyRet != PackageManager.INSTALL_FAILED_NO_MATCHING_ABIS) { Slog.w(TAG, "Failure copying 32 bit native libraries; copyRet=" +copyRet); return copyRet; } } if (Build.SUPPORTED_64_BIT_ABIS.length > 0) { copyRet = copyNativeBinariesForSupportedAbi(handle, libraryRoot, Build.SUPPORTED_64_BIT_ABIS, true /* use isa specific subdirs */); if (copyRet < 0 && copyRet != PackageManager.NO_NATIVE_LIBRARIES && copyRet != PackageManager.INSTALL_FAILED_NO_MATCHING_ABIS) { Slog.w(TAG, "Failure copying 64 bit native libraries; copyRet=" +copyRet); return copyRet; } } } else { String cpuAbiOverride = null; if (CLEAR_ABI_OVERRIDE.equals(abiOverride)) { cpuAbiOverride = null; } else if (abiOverride != null) { cpuAbiOverride = abiOverride; } String[] abiList = (cpuAbiOverride != null) ? new String[] { cpuAbiOverride } : Build.SUPPORTED_ABIS; if (Build.SUPPORTED_64_BIT_ABIS.length > 0 && cpuAbiOverride == null && hasRenderscriptBitcode(handle)) { abiList = Build.SUPPORTED_32_BIT_ABIS; } int copyRet = copyNativeBinariesForSupportedAbi(handle, libraryRoot, abiList, true /* use isa specific subdirs */); if (copyRet < 0 && copyRet != PackageManager.NO_NATIVE_LIBRARIES) { Slog.w(TAG, "Failure copying native libraries [errorCode=" + copyRet + "]"); return copyRet; } } return PackageManager.INSTALL_SUCCEEDED; } catch (IOException e) { Slog.e(TAG, "Copying native libraries failed", e); return PackageManager.INSTALL_FAILED_INTERNAL_ERROR; } }複製代碼

copyNativeBinariesWithOverride分別處理32位和64位so的拷貝，內部函數copyNativeBinariesForSupportedAbi首先會根據abilist去找對應的abi。

public static int copyNativeBinariesForSupportedAbi(Handle handle, File libraryRoot,
            String[] abiList, boolean useIsaSubdir) throws IOException {
        createNativeLibrarySubdir(libraryRoot);        /*
         * If this is an internal application or our nativeLibraryPath points to
         * the app-lib directory, unpack the libraries if necessary.
         */
        int abi = findSupportedAbi(handle, abiList);        if (abi >= 0) {            /*
             * If we have a matching instruction set, construct a subdir under the native
             * library root that corresponds to this instruction set.
             */
            final String instructionSet = VMRuntime.getInstructionSet(abiList[abi]);            final File subDir;            if (useIsaSubdir) {                final File isaSubdir = new File(libraryRoot, instructionSet);
                createNativeLibrarySubdir(isaSubdir);
                subDir = isaSubdir;
            } else {
                subDir = libraryRoot;
            }            int copyRet = copyNativeBinaries(handle, subDir, abiList[abi]);            if (copyRet != PackageManager.INSTALL_SUCCEEDED) {                return copyRet;
            }
        }        return abi;
    }複製代碼

findSupportedAbi內部實現是native函數，首先遍歷apk，若是so的全路徑中包含abilist中的abi字符串，則記錄該abi字符串的索引，最終返回全部記錄索引中最靠前的，即排在abilist中最前面的索引。

static int findSupportedAbi(JNIEnv *env, jlong apkHandle, jobjectArray supportedAbisArray) {    const int numAbis = env->GetArrayLength(supportedAbisArray);
    VectorsupportedAbis;    for (int i = 0; i < numAbis; ++i) {
        supportedAbis.add(new ScopedUtfChars(env,
            (jstring) env->GetObjectArrayElement(supportedAbisArray, i)));
    }
    ZipFileRO* zipFile = reinterpret_cast(apkHandle);    if (zipFile == NULL) {        return INSTALL_FAILED_INVALID_APK;
    }    UniquePtr it(NativeLibrariesIterator::create(zipFile));    if (it.get() == NULL) {        return INSTALL_FAILED_INVALID_APK;
    }
    ZipEntryRO entry = NULL;    char fileName[PATH_MAX];    int status = NO_NATIVE_LIBRARIES;    while ((entry = it->next()) != NULL) {        // We're currently in the lib/ directory of the APK, so it does have some native // code. We should return INSTALL_FAILED_NO_MATCHING_ABIS if none of the // libraries match. if (status == NO_NATIVE_LIBRARIES) { status = INSTALL_FAILED_NO_MATCHING_ABIS; } const char* fileName = it->currentEntry(); const char* lastSlash = it->lastSlash(); // Check to see if this CPU ABI matches what we are looking for. const char* abiOffset = fileName + APK_LIB_LEN; const size_t abiSize = lastSlash - abiOffset; for (int i = 0; i < numAbis; i++) { const ScopedUtfChars* abi = supportedAbis[i]; if (abi->size() == abiSize && !strncmp(abiOffset, abi->c_str(), abiSize)) { // The entry that comes in first (i.e. with a lower index) has the higher priority. if (((i < status) && (status >= 0)) || (status < 0) ) { status = i; } } } } for (int i = 0; i < numAbis; ++i) { delete supportedAbis[i]; } return status; }複製代碼

舉例說明，在某64位測試手機上的abi屬性顯示以下，它有2個abilist，分別對應該手機支持的32位和64位abi的字符串組。

當處理32位so拷貝時，findSupportedAbi索引返回以後，若返回爲0，則拷貝armeabi-v7a目錄下的so，若是爲1，則拷貝armeabi目錄下so。

拷貝so策略：

分別處理32位和64位abi目錄的so拷貝，abi由遍歷apk結果的全部so中符合abilist列表的最靠前的序號決定，而後拷貝該abi目錄下的so文件。

策略問題：

策略假定每一個abi目錄下的so都放置徹底的，這是和2.3.6同樣的處理邏輯，存在遺漏拷貝so的可能。

0x5 建議

針對android系統的這些拷貝策略的問題，咱們給出了一些配置so的建議：

1）針對armeabi和armeabi-v7a兩種ABI

方法1：因爲armeabi-v7a指令集兼容armeabi指令集，因此若是損失一些應用的性能是能夠接受的，同時不但願保留庫的兩份拷貝，能夠移除armeabi-v7a目錄和其下的庫文件，只保留armeabi目錄；好比apk使用第三方的so只有armeabi這一種abi時，能夠考慮去掉apk中lib目錄下armeabi-v7a目錄。

方法2：在armeabi和armeabi-v7a目錄下各放入一份so；

2）針對x86

目前市面上的x86機型，爲了兼容arm指令，基本都內置了libhoudini模塊，即二進制轉碼支持，該模塊負責把ARM指令轉換爲X86指令，因此若是是出於apk包大小的考慮，而且能夠接受一些性能損失，能夠選擇刪掉x86庫目錄，x86下配置的armeabi目錄的so庫同樣能夠正常加載使用；

3）針對64位ABI

若是app開發者打算支持64位，那麼64位的so要放全，不然能夠選擇不單獨編譯64位的so，所有使用32位的so，64位機型默認支持32位so的加載。好比apk使用第三方的so只有32位abi的so，能夠考慮去掉apk中lib目錄下的64位abi子目錄，保證apk安裝後正常使用。

0x6 備註

其實本文是由於在Android的so加載上遇到不少坑，相信不少朋友都遇到過UnsatisfiedLinkError這個錯誤，反應在用戶的機型上也是千差萬別，可是有沒有想過，可能不是apk邏輯的問題，而是Android系統在安裝APK的時候，因爲PackageManager的問題，並無拷貝相應的SO呢？能夠參考下面第4個連接，做者給出瞭解決方案，就是當出現UnsatisfiedLinkError錯誤時，手動拷貝so來解決的。

參考文章：

android源碼：https://android.googlesource.com/platform/frameworks/base

apk安裝過程及原理說明：http://blog.csdn.net/hdhd588/article/details/6739281

UnsatisfiedLinkError的錯誤及解決方案：

medium.com/keepsafe-en…

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