From version 3.0 and upwards, xcache does not load using the zend_extension directive in its ini file. The xcache.ini file that the package provides for PHP 5.4 uses the following line: zend_extension=/usr/lib64/php5.4/lib/extensions/no-debug-non-zts-20100525/xcache.so which does not work. Instead, this must be changed to: extension=xcache.so This applies for version 5.4 of the apache2 php module.
Did you perhaps update without updating the configuration files?
(In reply to comment #1) > Did you perhaps update without updating the configuration files? You're right. I deleted xcache.ini from both php targets and emerged xcache. Both inis are correct. I apologize for the noise.