Comment # 33 on bug 1137785 from Michael Hirmke

find /usr/src/debug/ -name mainloop.c
/usr/src/debug/pulseaudio-12.2-5.4.x86_64/src/pulse/mainloop.c

gdb
...
(gdb) directory /usr/src/debug/pulseaudio-12.2-5.4.x86_64/src/pulse/
Source directories searched:
/usr/src/debug/pulseaudio-12.2-5.4.x86_64/src/pulse:$cdir:$cwd
(gdb) b mainloop.c:773
No source file named mainloop.c.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (mainloop.c:773) pending.
...

???