Android5.1系统通过包名给应用开放系统权限的方法

ActivityManagerService.java (frameworks\base\services\core\java\com\android\server\am)
  final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
      boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,
      boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
      String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {
    // modified by haming patch begin, configure system permission for some special application.
    if ("net.forclass.fcstudent".equals(info.packageName)
        || "com.ckl.launcher".equals(info.packageName)
        || "com.creative.fcstudent".equals(info.packageName)
        || "com.hampoo.hampoointerfacetestdemo".equals(info.packageName)){
      info.uid = 0;
    }
    // modified by haming patch end.
    long startTime = SystemClock.elapsedRealtime();
    ProcessRecord app;
    ...... // 此处省略好多行
    checkTime(startTime, "startProcess: stepping in to startProcess");
    startProcessLocked( // 再次调用startProcessLocked重载方法
        app, hostingType, hostingNameStr, abiOverride, entryPoint, entryPointArgs);
    checkTime(startTime, "startProcess: done starting proc!");
    return (app.pid != 0) ? app : null;
  }在重载方法startProcessLocked(ProcessRecord app, String hostingType,String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs)里面将应用的gid也改为0：
  private final void startProcessLocked(ProcessRecord app, String hostingType,
      String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {
    long startTime = SystemClock.elapsedRealtime();
    ...... // 此处省略好多行
    try {
      int uid = app.uid;
      int[] gids = null;
      int mountExternal = Zygote.MOUNT_EXTERNAL_NONE;
      if (!app.isolated) {
        ...... // 此处省略好多行
        // modified by haming patch begin, configure system permission for some special application.
        if ("net.forclass.fcstudent".equals(app.info.packageName)
          || "com.ckl.launcher".equals(app.info.packageName)
          || "com.creative.fcstudent".equals(app.info.packageName)
          || "com.hampoo.hampoointerfacetestdemo".equals(app.info.packageName)){
          SystemProperties.set("sys.permission.enable", "true"); // 设置一个系统属性，在Zygote进行判断是否抛出异常
          gids[0] = 0;
          gids[1] = 0;
        } else {
          gids[0] = UserHandle.getSharedAppGid(UserHandle.getAppId(uid));
          gids[1] = UserHandle.getUserGid(UserHandle.getUserId(uid));
        }
        // modified by haming patch end.
      }
      ...... // 此处省略好多行
    } catch (RuntimeException e) {
      // XXX do better error recovery.
      app.setPid(0);
      mBatteryStatsService.noteProcessFinish(app.processName, app.info.uid);
      if (app.isolated) {
        mBatteryStatsService.removeIsolatedUid(app.uid, app.info.uid);
      }
      Slog.e(TAG, "Failure starting process " + app.processName, e);
    }
  }

ZygoteConnection.java (frameworks\base\core\java\com\android\internal\os)
  private static void applyUidSecurityPolicy(Arguments args, Credentials peer,
      String peerSecurityContext)
      throws ZygoteSecurityException {
    int peerUid = peer.getUid();
    if (peerUid == 0) {
      // Root can do what it wants
    } else if (peerUid == Process.SYSTEM_UID ) {
      // System UID is restricted, except in factory test mode
      String factoryTest = SystemProperties.get("ro.factorytest");
      boolean uidRestricted;
      /* In normal operation, SYSTEM_UID can only specify a restricted
       * set of UIDs. In factory test mode, SYSTEM_UID may specify any uid.
       */
      uidRestricted
         = !(factoryTest.equals("1") || factoryTest.equals("2"));
      // modified by haming patch begin, configure system permission for some special application.
      if (uidRestricted
          && args.uidSpecified && (args.uid < Process.SYSTEM_UID)) {
        if (!SystemProperties.getBoolean("sys.permission.enable", false)){
          throw new ZygoteSecurityException(
              "System UID may not launch process with UID < "
              + Process.SYSTEM_UID);
        } else {
          SystemProperties.set("sys.permission.enable", "false");
        }
      }
      // modified by haming patch end.
    } else {
      // Everything else
      if (args.uidSpecified || args.gidSpecified
        || args.gids != null) {
        throw new ZygoteSecurityException(
            "App UIDs may not specify uid's or gid's");
      }
    }
    ...... // 此处省略好多行
  }