Index: head/lib/libthr/thread/thr_attr.c
===================================================================
--- head/lib/libthr/thread/thr_attr.c
+++ head/lib/libthr/thread/thr_attr.c
@@ -607,7 +607,7 @@
 			/* Kernel checks invalid bits, we check it here too. */
 			size_t i;
 			for (i = kern_size; i < cpusetsize; ++i) {
-				if (((char *)cpusetp)[i])
+				if (((const char *)cpusetp)[i])
 					return (EINVAL);
 			}
 		}
Index: head/lib/libthr/thread/thr_exit.c
===================================================================
--- head/lib/libthr/thread/thr_exit.c
+++ head/lib/libthr/thread/thr_exit.c
@@ -119,7 +119,8 @@
 #endif /* PIC */
 
 static void
-thread_unwind_cleanup(_Unwind_Reason_Code code, struct _Unwind_Exception *e)
+thread_unwind_cleanup(_Unwind_Reason_Code code __unused,
+    struct _Unwind_Exception *e __unused)
 {
 	/*
 	 * Specification said that _Unwind_Resume should not be used here,
@@ -130,10 +131,10 @@
 }
 
 static _Unwind_Reason_Code
-thread_unwind_stop(int version, _Unwind_Action actions,
-	int64_t exc_class,
-	struct _Unwind_Exception *exc_obj,
-	struct _Unwind_Context *context, void *stop_parameter)
+thread_unwind_stop(int version __unused, _Unwind_Action actions,
+	int64_t exc_class __unused,
+	struct _Unwind_Exception *exc_obj __unused,
+	struct _Unwind_Context *context, void *stop_parameter __unused)
 {
 	struct pthread *curthread = _get_curthread();
 	struct pthread_cleanup *cur;
Index: head/lib/libthr/thread/thr_sig.c
===================================================================
--- head/lib/libthr/thread/thr_sig.c
+++ head/lib/libthr/thread/thr_sig.c
@@ -441,7 +441,7 @@
 }
 
 void
-_thr_sigact_unload(struct dl_phdr_info *phdr_info)
+_thr_sigact_unload(struct dl_phdr_info *phdr_info __unused)
 {
 #if 0
 	struct pthread *curthread = _get_curthread();
Index: head/lib/libthr/thread/thr_spec.c
===================================================================
--- head/lib/libthr/thread/thr_spec.c
+++ head/lib/libthr/thread/thr_spec.c
@@ -42,7 +42,7 @@
 
 #include "thr_private.h"
 
-struct pthread_key _thread_keytable[PTHREAD_KEYS_MAX];
+static struct pthread_key _thread_keytable[PTHREAD_KEYS_MAX];
 
 __weak_reference(_pthread_key_create, pthread_key_create);
 __weak_reference(_pthread_key_delete, pthread_key_delete);
Index: head/lib/libthr/thread/thr_stack.c
===================================================================
--- head/lib/libthr/thread/thr_stack.c
+++ head/lib/libthr/thread/thr_stack.c
@@ -290,6 +290,19 @@
 		return (-1);
 }
 
+/*
+ * Disable this warning from clang:
+ *
+ * cast from 'char *' to
+ *    'struct stack *' increases required alignment from 1 to 8
+ *    [-Werror,-Wcast-align]
+ *                 spare_stack = (struct stack *)
+ */
+#ifdef __clang__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wcast-align"
+#endif
+
 /* This function must be called with _thread_list_lock held. */
 void
 _thr_stack_free(struct pthread_attr *attr)
@@ -316,3 +329,7 @@
 		attr->stackaddr_attr = NULL;
 	}
 }
+
+#ifdef __clang__
+#pragma GCC diagnostic pop
+#endif
Index: head/lib/libthr/thread/thr_symbols.c
===================================================================
--- head/lib/libthr/thread/thr_symbols.c
+++ head/lib/libthr/thread/thr_symbols.c
@@ -37,6 +37,10 @@
 
 #include "thr_private.h"
 
+#ifdef __clang__
+#pragma GCC diagnostic ignored "-Wmissing-variable-declarations"
+#endif
+
 /* A collection of symbols needed by debugger */
 
 /* int _libthr_debug */
Index: head/lib/libthr/thread/thr_umtx.h
===================================================================
--- head/lib/libthr/thread/thr_umtx.h
+++ head/lib/libthr/thread/thr_umtx.h
@@ -44,7 +44,7 @@
 int __thr_umutex_lock_spin(struct umutex *mtx, uint32_t id) __hidden;
 int __thr_umutex_timedlock(struct umutex *mtx, uint32_t id,
 	const struct timespec *timeout) __hidden;
-int __thr_umutex_unlock(struct umutex *mtx, uint32_t id) __hidden;
+int __thr_umutex_unlock(struct umutex *mtx) __hidden;
 int __thr_umutex_trylock(struct umutex *mtx) __hidden;
 int __thr_umutex_set_ceiling(struct umutex *mtx, uint32_t ceiling,
 	uint32_t *oldceiling) __hidden;
@@ -155,7 +155,7 @@
 		if (atomic_cmpset_rel_32(&mtx->m_owner, id, noncst ?
 		    UMUTEX_RB_NOTRECOV : UMUTEX_UNOWNED))
 			return (0);
-		return (__thr_umutex_unlock(mtx, id));
+		return (__thr_umutex_unlock(mtx));
 	}
 
 	do {
Index: head/lib/libthr/thread/thr_umtx.c
===================================================================
--- head/lib/libthr/thread/thr_umtx.c
+++ head/lib/libthr/thread/thr_umtx.c
@@ -168,7 +168,7 @@
 }
 
 int
-__thr_umutex_unlock(struct umutex *mtx, uint32_t id)
+__thr_umutex_unlock(struct umutex *mtx)
 {
 
 	return (_umtx_op_err(mtx, UMTX_OP_MUTEX_UNLOCK, 0, 0, 0));