I've searched but can't find any reference to this...
Compiling IO::KQueue on Snow Leopard I get the following warning:
KQueue.xs: In function 'XS_IO__KQueue_kevent':
KQueue.xs:71: warning: format not a string literal and no format arguments
Yet that line is just:
Newxz(ke, max_events, struct kevent);
Which seems to me pretty standard perl, and no format strings involved (though Newxz expands quite a few macros).