http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33925
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-04-18 17:01:23 UTC --- (In reply to comment #3) > First, I think the C++ standard forbids a function from having a null > address: But GCC extensions allow it, see the weakref attribute: http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#index-g_t_0040code_007bweakref_007d-attribute-2648 That's used (among other places) by GCC's pthreads abstraction layer to declare a weak alias to pthread_create, which has a null address unless libpthread is linked to. Testing whether the address is null (i.. whether the application was linked to libpthread) is used for important optimisations.
