As of commit 22201dde773e5404f80baa1f59768e88d97a322a, calling
(profiler-cpu-log) while the CPU profiler is not running causes Emacs to
crash with a segfault.  I have confirmed this issue also appears at
f69b822fb0e804a13ff7a4eb55fc2ae618e0de72, which was the tip of the
master branch at the time of writing.

To reproduce, simply run:
$ emacs -Q --batch --eval '(profiler-cpu-log)'

The gdb backtrace is attached to this email.