Different behavior of override weak function in shared library between OS X and Android

Question

I am encountering a different behavior between OS X and Android:

• There is a weak function foo in my shared library,
• I want to override it

Answer 1

Android doesn't support weak symbol override.

In the recent release android-5.0.2_r1, see the comment at line 539 in linker.cpp source code

/*
 *
 * Notes on weak symbols:
 * The ELF specs are ambigious about treatment of weak definitions in
 * dynamic linking.  Some systems return the first definition found
 * and some the first non-weak definition.   This is system dependent.
 * Here we return the first definition found for simplicity.
 */

This comment exists from version 2.2_r1 (which is in linker.c) to newest version 5.0.2_r1

Answer 2

Android dynamic linker does in fact support weak symbols. The problem is this particular case is that library is compiled with -Bsymbolic (to check this run "readelf -d libshared.so").

The work around this is to use '-Wl,-shared' instead of '-shared' when linking the library.

Please see https://code.google.com/p/android/issues/detail?id=68956 for details and workaround.