+#define SIG_MEMORY_FAULT SIGSEGV
+/* Sometime in late 2005 FreeBSD was changed to signal SIGSEGV instead
+ * of SIGBUS for memory faults, as required by POSIX. In order to
+ * support both new and old FreeBSD at the same time, both signals are
+ * hooked to the GC write barrier machinery. If you're reading this
+ * message in the far future where FreeBSD 6 and earlier are just
+ * quaint memories, feel free to delete this hack (and any code that's
+ * #ifdef SIG_MEMORY_FAULT2'ed). -- JES, 2005-12-30
+ */
+#define SIG_MEMORY_FAULT2 SIGBUS
+
+#define SIG_INTERRUPT_THREAD (SIGINFO)
+#define SIG_STOP_FOR_GC (SIGUSR1)
+#define SIG_RESUME_FROM_GC (SIGUSR2)