+ pthread_mutex_unlock(&modify_ldt_lock);
+
+ /* now %fs:0 refers to the current thread. Useful! Less usefully,
+ * Linux/x86 isn't capable of reporting a faulting si_addr on a
+ * segment as defined above (whereas faults on the segment that %gs
+ * usually points are reported just fine...). As a special
+ * workaround, we store each thread structure's absolute address as
+ * as slot in itself, so that within the thread,
+ * movl %fs:SELFPTR_OFFSET,x
+ * stores the absolute address of %fs:0 into x.
+ */
+#ifdef LISP_FEATURE_SB_SAFEPOINT
+ thread->selfptr = thread;
+#endif