The behaviour of these functions is affected by settings in php.ini.
INI_SYSTEM
Here's a short explanation of the configuration directives.
uopz.disable
If enabled, uopz should stop having any effect on the engine.
uopz.exit
Whether to allow the execution of exit opcodes or not. This setting can be overridden during runtime by calling uopz_allow_exit.
uopz.overloads
Enables the ability to use uopz_overload.
Note: When running with OPcache enabled, it may be necessary to disable all OPcache optimizations (opcache.optimization_level=0).
opcache.optimization_level=0