CODEWITHSUNDEEP
androidc++linuxshared-librarieself
user1733773
user1733773

Reputation: 360

dlsym: undefined symbol, Android N

I would like to read value from the Android runtime shared library in my application. Since Android 5, when the new runtime was introduced and libart.so has first appeared, I am doing it successfully with this code:

 std::unique_ptr<void, int(*)(void*)> handle { 
     dlopen("libart.so", RTLD_NOW | RTLD_GLOBAL),
     &dlclose
 };

constexpr char THREAD_KEY_NAME[] = "_ZN3art6Thread17pthread_key_self_E";
key_ = static_cast<pthread_key_t *>(dlsym(handle.get(), THREAD_KEY_NAME));

LOG("Current thread: ", key_);

I'm testing this code on Android N simulator, and it fails! dlsym returns: 

undefined symbol: _ZN3art6Thread17pthread_key_self_E

I think "OK, there is no symbol now", so I pull the libart.so from simulator and see:

% ./i686-linux-android-nm ~/Desktop/libart.so | grep pthread_key
00736ea0 B _ZN3art6Thread17pthread_key_self_E

hmm...

% ./i686-linux-android-objdump -T ~/Desktop/libart.so | grep pthread_key
00736ea0 g    DO .bss   00000004  Base        .protected _ZN3art6Thread17pthread_key_self_E

hmm..

  % ./i686-linux-android-readelf -a ~/Desktop/libart.so | grep pthread_key_self
  %

OK, empty there :(

So, while I'm not fully expert in these things, i have some questions:

  1. Why is readelf output is empty? There is some flags i forgot?
  2. What does .protected means in objdump output? I have read some things about it but don't really understand. May be you can get good explanation?
  3. Why dlsym returns error on new versions of Android? What the difference?

BTW, I dumped /proc/self/maps file for my application on both Android versions and grep libart.so gives me:

Thanks for any information!

upd: I see there is two libart.so on Android N, and /system/fake-libs/libart.so is empty. I suppose there is a problem, but dlopen("/system/lib/libart.so", ...) does not works :(

Upvotes: 4

Views: 2616

Answers (1)

muyiou
muyiou

Reputation: 669

In Android N you can not open some private so file(https://developer.android.com/about/versions/nougat/android-7.0-changes.html#ndk)

But you can open libart.so for Android-N use this: https://github.com/crmulliner/adbi/blob/master/hijack/hijack.c or https://github.com/avs333/Nougat_dlfunctions

Upvotes: 1

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