Thanks for reporting this. I reproduced the problem on Fedora 23 x86-64. It appears to be a bug in link-time optimization. The symbol __malloc_initialize_hook is marked external in alloc.o, but merely static (private) in temacs: $ nm -o alloc.o temacs | grep __malloc_init alloc.o:00000000002e0a40 D __malloc_initialize_hook temacs:0000000000b25340 d __malloc_initialize_hook We used to define this variable in emacs.o, and we now do it in alloc.o. Possibly we were lucky that the code ever worked, as I guess the LTO bug strikes depending on link time order. I installed the attached patch, which works around the bug for me. Please give it a try. Are any of you connected to the folks who implement LTO? It'd be nice to report this bug to them somehow.