eval.c:4664
static inline void
stack_check()
{
    static int overflowing = 0;

    if (!overflowing && ruby_stack_check()) {
	int state;
	overflowing = 1;
	PUSH_TAG(PROT_NONE);
	if ((state = EXEC_TAG()) == 0) {
	    rb_exc_raise(sysstack_error);
	}
	POP_TAG();
	overflowing = 0;
	JUMP_TAG(state);
    }
}
