Has Rawhide incorporated some of Florian Weimer's malloc patches? If so, 
this is almost surely causing the problem. I will CC: Florian to give 
him a heads-up. See:

https://sourceware.org/ml/libc-alpha/2016-06/msg00211.html

https://sourceware.org/bugzilla/show_bug.cgi?id=19564

I am surprised that you can use valgrind. Valgrind does not work on 
Emacs in Fedora 23 because it mishandles the way Emacs dumps and 
restores. I can use Valgrind only on temacs, not on Emacs itself. The 
fact that you can use Valgrind on a dumped Emacs suggests that some of 
the malloc patches have been installed on Rawhide.


For what it's worth, when I try to use valgrind on Fedora 23, I run into 
what appears to be a valgrind bug that prevents Emacs from working. I 
just now filed it here:

https://bugzilla.redhat.com/show_bug.cgi?id=1344082

I ran valgrind as follows:

valgrind --log-fd=3 --suppressions=valgrind.supp ./temacs 3>/tmp/vg.log

with the attached valgrind.supp file, and Emacs (emacs-25 branch, built 
with 'configure --with-x=no') says "Failed select: Bad address" due to 
the valgrind bug. How do you use valgrind on Rawhide?