Android系统库豁免列表

 在bionic/linker/linker.cpp中有一个系统库函数的豁免列表，但是只有target sdk version小于24才能被豁免。

static bool is_exempt_lib(android_namespace_t* ns, const char* name, const soinfo* needed_by) {
  static const char* const kLibraryExemptList[] = {
    "libandroid_runtime.so",
    "libbinder.so",
    "libcrypto.so",
    "libcutils.so",
    "libexpat.so",
    "libgui.so",
    "libmedia.so",
    "libnativehelper.so",
    "libssl.so",
    "libstagefright.so",
    "libsqlite.so",
    "libui.so",
    "libutils.so",
    nullptr
  };

  // If you're targeting N, you don't get the exempt-list.
  if (get_application_target_sdk_version() >= 24) {
    return false;
  }

  // if the library needed by a system library - implicitly assume it
  // is exempt unless it is in the list of shared libraries for one or
  // more linked namespaces
  if (needed_by != nullptr && is_system_library(needed_by->get_realpath())) {
    return !maybe_accessible_via_namespace_links(ns, name);
  }

  // if this is an absolute path - make sure it points to /system/lib(64)
  if (name[0] == '/' && dirname(name) == kSystemLibDir) {
    // and reduce the path to basename
    name = basename(name);
  }

  for (size_t i = 0; kLibraryExemptList[i] != nullptr; ++i) {
    if (strcmp(name, kLibraryExemptList[i]) == 0) {
      return true;
    }
  }

  return false;
}