[Mobile-sig] [Python-Dev] Import Fails in setup.py On Android

[Frank, Matthew I]

On Tuesday, February 17, 2015 4:40 PM, Cyd Haselton wrote:
> Some additional import failures.  I;ve compared build instructions for these modules
> and can't find anything that stands out as to why one module will import and the other
> doesn't:
[...]
> ImportError: dlopen failed: cannot locate symbol "PyErr_BadArgument" referenced by
> "array.cpython-34m.so"...
[...]
> ImportError: dlopen failed: cannot locate symbol "PyMem_Malloc" referenced by
> "_random.cpython-34m.so"...
[...]
> ImportError: dlopen failed: cannot locate symbol "PyMem_Malloc" referenced by
> "zlib.cpython-34m.so"...
[...]
> ImportError: dlopen failed: cannot locate symbol "PySequence_GetItem" referenced by
> "_bisect.cpython-34m.so"...
[...]
> ImportError: dlopen failed: cannot locate symbol "PyErr_SetNone" referenced by
> "_pickle.cpython-34m.so"...

All those missing symbols are defined in libpython3.4m.so.  I suspect that array.cpython-34m.so, _random.cpython-34m.so, zlib.cpython-34m.so, _bisect.cpython-34m.so and _pickle.cpython-34m.so were all compiled without the correct -lpython3 flag.  I suspect that some other imports are not displaying this problem because, although they also are not compiled with -lpython3, they aren't trying to access symbols from libpython3.4m.so.

If I'm correct, the problem here is with Android's broken dlopen().  On Linux (and every other Unix I'm aware of) when Executable A links B then tries to dlopen C, if C needs to access symbols from B it just succeeds (whether or not you linked C with "-lB".)  On Android you _must_ link C against "-lB" for this to work.  This is a known bug in Android's loader and won't be fixed, because the supposed security advantages of not accidentally linking something you didn't mean to link supposedly outweigh the disadvantages of not being able to correctly compile linux packages for Android.

I ran into only a few instances of these when getting Python 3.4 to cross compile to Android, and none with missing -lpython3 flags (most were missing -lm flags).  But I'm not running setup.py on the Android side.  I'm running on it the Linux host (using the Python interpreter on the Linux host.)

-Matt