+ /* Skip the allocation trap and the write of the updated free
+ * pointer back to the allocation region. This is two
+ * instructions when threading is enabled and four instructions
+ * otherwise. */
+#ifdef LISP_FEATURE_SB_THREAD
+ (*os_context_pc_addr(context)) = pc + 2;
+#else
+ (*os_context_pc_addr(context)) = pc + 4;
+#endif