diff --git a/ChangeLog b/ChangeLog
index 0fedd47..fbb3f3f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,43 @@
+2019-05-04  Mike Crowe  <mac@mcrowe.com>
+
+	nptl: Add clockid parameter to futex timed wait calls
+
+	* sysdeps/nptl/lowlevellock-futex.h,
+	sysdeps/unix/sysv/linux/lowlevellock-futex.h: Replace
+	lll_futex_timed_wait_bitset with lll_futex_clock_wait_bitset that
+	takes a clockid rather than a special clockbit.
+
+	* sysdeps/nptl/lowlevellock-futex.h: Add
+	lll_futex_supported_clockid so that client functions can check
+	whether their clockid parameter is valid even if they don't
+	ultimately end up calling lll_futex_clock_wait_bitset.
+
+	* sysdeps/nptl/futex-internal.h,
+	sysdeps/unix/sysv/linux/futex-internal.h
+	(futex_abstimed_wait, futex_abstimed_wait_cancelable): Add
+	clockid_t parameter to indicate which clock the absolute time
+	passed should be measured against. Pass that clockid onto
+	lll_futex_clock_wait_bitset. Add invalid clock as reason for
+	returning -EINVAL.
+
+	* sysdeps/nptl/futex-internal.h,
+	sysdeps/unix/sysv/linux/futex-internal.h: Introduce
+	futex_abstimed_supported_clockid so that client functions can check
+	whether their clockid parameter is valid even if they don't
+	ultimately end up calling futex_abstimed_wait.
+
+	* nptl/pthread_cond_wait.c (__pthread_cond_wait_common): Remove
+	code to calculate relative timeout for
+	__PTHREAD_COND_CLOCK_MONOTONIC_MASK and just pass CLOCK_MONOTONIC
+	or CLOCK_REALTIME as required to futex_abstimed_wait_cancelable.
+
+	* nptl/pthread_rwlock_common (__pthread_rwlock_rdlock_full)
+	(__pthread_wrlock_full), nptl/sem_waitcommon (do_futex_wait): Pass
+	additional CLOCK_REALTIME to futex_abstimed_wait_cancelable.
+
+	* nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock):
+	Switch to lll_futex_clock_wait_bitset and pass CLOCK_REALTIME
+
 2019-05-02  Mike Crowe  <mac@mcrowe.com>
 
 	* nptl/tst-abstime.c: Use libsupport.
diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
index 9a0f29e..7385562 100644
--- a/nptl/pthread_cond_wait.c
+++ b/nptl/pthread_cond_wait.c
@@ -509,35 +509,15 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
 		 values despite them being valid.  */
 	      if (__glibc_unlikely (abstime->tv_sec < 0))
 	        err = ETIMEDOUT;
-
-	      else if ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0)
-		{
-		  /* CLOCK_MONOTONIC is requested.  */
-		  struct timespec rt;
-		  if (__clock_gettime (CLOCK_MONOTONIC, &rt) != 0)
-		    __libc_fatal ("clock_gettime does not support "
-				  "CLOCK_MONOTONIC\n");
-		  /* Convert the absolute timeout value to a relative
-		     timeout.  */
-		  rt.tv_sec = abstime->tv_sec - rt.tv_sec;
-		  rt.tv_nsec = abstime->tv_nsec - rt.tv_nsec;
-		  if (rt.tv_nsec < 0)
-		    {
-		      rt.tv_nsec += 1000000000;
-		      --rt.tv_sec;
-		    }
-		  /* Did we already time out?  */
-		  if (__glibc_unlikely (rt.tv_sec < 0))
-		    err = ETIMEDOUT;
-		  else
-		    err = futex_reltimed_wait_cancelable
-			(cond->__data.__g_signals + g, 0, &rt, private);
-		}
 	      else
 		{
-		  /* Use CLOCK_REALTIME.  */
+		  const clockid_t clockid =
+		    ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0) ?
+		    CLOCK_MONOTONIC : CLOCK_REALTIME;
+
 		  err = futex_abstimed_wait_cancelable
-		      (cond->__data.__g_signals + g, 0, abstime, private);
+                    (cond->__data.__g_signals + g, 0, clockid, abstime,
+                     private);
 		}
 	    }
 
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index 270b072..d4d11cc 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -266,8 +266,8 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex,
 	  assume_other_futex_waiters |= FUTEX_WAITERS;
 
 	  /* Block using the futex.  */
-	  int err = lll_futex_timed_wait_bitset (&mutex->__data.__lock,
-	      oldval, abstime, FUTEX_CLOCK_REALTIME,
+	  int err = lll_futex_clock_wait_bitset (&mutex->__data.__lock,
+	      oldval, CLOCK_REALTIME, abstime,
 	      PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
 	  /* The futex call timed out.  */
 	  if (err == -ETIMEDOUT)
diff --git a/nptl/pthread_rwlock_common.c b/nptl/pthread_rwlock_common.c
index 2560734..89ba21a 100644
--- a/nptl/pthread_rwlock_common.c
+++ b/nptl/pthread_rwlock_common.c
@@ -319,7 +319,7 @@ __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
 		{
 		  int private = __pthread_rwlock_get_private (rwlock);
 		  int err = futex_abstimed_wait (&rwlock->__data.__readers,
-						 r, abstime, private);
+						 r, CLOCK_REALTIME, abstime, private);
 		  /* We ignore EAGAIN and EINTR.  On time-outs, we can just
 		     return because we don't need to clean up anything.  */
 		  if (err == ETIMEDOUT)
@@ -447,7 +447,7 @@ __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
 	    continue;
 	  int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
 					 1 | PTHREAD_RWLOCK_FUTEX_USED,
-					 abstime, private);
+					 CLOCK_REALTIME, abstime, private);
 	  if (err == ETIMEDOUT)
 	    {
 	      /* If we timed out, we need to unregister.  If no read phase
@@ -707,7 +707,7 @@ __pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
 	  may_share_futex_used_flag = true;
 	  int err = futex_abstimed_wait (&rwlock->__data.__writers_futex,
 					 1 | PTHREAD_RWLOCK_FUTEX_USED,
-					 abstime, private);
+					 CLOCK_REALTIME, abstime, private);
 	  if (err == ETIMEDOUT)
 	    {
 	      if (prefer_writer)
@@ -806,7 +806,7 @@ __pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
 	    continue;
 	  int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
 					 PTHREAD_RWLOCK_FUTEX_USED,
-					 abstime, private);
+					 CLOCK_REALTIME, abstime, private);
 	  if (err == ETIMEDOUT)
 	    {
 	      if (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP)
diff --git a/nptl/sem_waitcommon.c b/nptl/sem_waitcommon.c
index 5646bea..425d040 100644
--- a/nptl/sem_waitcommon.c
+++ b/nptl/sem_waitcommon.c
@@ -109,11 +109,13 @@ do_futex_wait (struct new_sem *sem, const struct timespec *abstime)
 
 #if __HAVE_64B_ATOMICS
   err = futex_abstimed_wait_cancelable (
-      (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0, abstime,
+      (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0,
+      CLOCK_REALTIME, abstime,
       sem->private);
 #else
   err = futex_abstimed_wait_cancelable (&sem->value, SEM_NWAITERS_MASK,
-					abstime, sem->private);
+					CLOCK_REALTIME, abstime,
+					sem->private);
 #endif
 
   return err;
diff --git a/sysdeps/nptl/futex-internal.h b/sysdeps/nptl/futex-internal.h
index 86a0818..54b7319 100644
--- a/sysdeps/nptl/futex-internal.h
+++ b/sysdeps/nptl/futex-internal.h
@@ -159,16 +159,23 @@ futex_reltimed_wait_cancelable (unsigned int* futex_word,
 				unsigned int expected,
 			        const struct timespec* reltime, int private);
 
+/* Check whether the specified clockid is supported by
+   futex_abstimed_wait and futex_abstimed_wait_cancelable. */
+static __always_inline int
+futex_abstimed_supported_clockid (clockid_t clockid);
+
 /* Like futex_reltimed_wait, but the provided timeout (ABSTIME) is an
    absolute point in time; a call will time out after this point in time.  */
 static __always_inline int
 futex_abstimed_wait (unsigned int* futex_word, unsigned int expected,
+		     clockid_t clockid,
 		     const struct timespec* abstime, int private);
 
 /* Like futex_reltimed_wait but is a POSIX cancellation point.  */
 static __always_inline int
 futex_abstimed_wait_cancelable (unsigned int* futex_word,
 				unsigned int expected,
+				clockid_t clockid,
 			        const struct timespec* abstime, int private);
 
 /* Atomically wrt other futex operations on the same futex, this unblocks the
diff --git a/sysdeps/nptl/lowlevellock-futex.h b/sysdeps/nptl/lowlevellock-futex.h
index 63d917d..35fcfbb 100644
--- a/sysdeps/nptl/lowlevellock-futex.h
+++ b/sysdeps/nptl/lowlevellock-futex.h
@@ -43,10 +43,15 @@
 #define lll_futex_timed_wait(futexp, val, timeout, private)             \
   -ENOSYS
 
-/* If CLOCKBIT is zero, this is identical to lll_futex_timed_wait.
-   If CLOCKBIT has FUTEX_CLOCK_REALTIME set, then it's the same but
-   TIMEOUT is counted by CLOCK_REALTIME rather than CLOCK_MONOTONIC.  */
-#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
+/* Verify whether the supplied clockid is supported by
+   lll_futex_clock_wait_bitset */
+#define lll_futex_supported_clockid(clockid)				\
+  (0)
+
+/* Wait until a lll_futex_wake call on FUTEXP, or the absolute TIMEOUT
+   measured against CLOCKID elapses. CLOCKID may be CLOCK_REALTIME or
+   CLOCK_MONOTONIC. */
+#define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
   -ENOSYS
 
 /* Wake up up to NR waiters on FUTEXP.  */
diff --git a/sysdeps/unix/sysv/linux/futex-internal.h b/sysdeps/unix/sysv/linux/futex-internal.h
index 55f0fab..68bfe7e 100644
--- a/sysdeps/unix/sysv/linux/futex-internal.h
+++ b/sysdeps/unix/sysv/linux/futex-internal.h
@@ -162,15 +162,24 @@ futex_reltimed_wait_cancelable (unsigned int *futex_word,
 
 /* See sysdeps/nptl/futex-internal.h for details.  */
 static __always_inline int
+futex_abstimed_supported_clockid (clockid_t clockid)
+{
+  return lll_futex_supported_clockid (clockid);
+}
+
+/* See sysdeps/nptl/futex-internal.h for details.  */
+static __always_inline int
 futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
+		     clockid_t clockid,
 		     const struct timespec *abstime, int private)
 {
   /* Work around the fact that the kernel rejects negative timeout values
      despite them being valid.  */
   if (__glibc_unlikely ((abstime != NULL) && (abstime->tv_sec < 0)))
     return ETIMEDOUT;
-  int err = lll_futex_timed_wait_bitset (futex_word, expected, abstime,
-					 FUTEX_CLOCK_REALTIME, private);
+  int err = lll_futex_clock_wait_bitset (futex_word, expected,
+					 clockid, abstime,
+					 private);
   switch (err)
     {
     case 0:
@@ -180,9 +189,10 @@ futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
       return -err;
 
     case -EFAULT: /* Must have been caused by a glibc or application bug.  */
-    case -EINVAL: /* Either due to wrong alignment or due to the timeout not
-		     being normalized.  Must have been caused by a glibc or
-		     application bug.  */
+    case -EINVAL: /* Either due to wrong alignment, unsupported
+		     clockid or due to the timeout not being
+		     normalized. Must have been caused by a glibc or
+		     application bug. */
     case -ENOSYS: /* Must have been caused by a glibc bug.  */
     /* No other errors are documented at this time.  */
     default:
@@ -194,6 +204,7 @@ futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
 static __always_inline int
 futex_abstimed_wait_cancelable (unsigned int *futex_word,
 				unsigned int expected,
+				clockid_t clockid,
 			        const struct timespec *abstime, int private)
 {
   /* Work around the fact that the kernel rejects negative timeout values
@@ -202,8 +213,9 @@ futex_abstimed_wait_cancelable (unsigned int *futex_word,
     return ETIMEDOUT;
   int oldtype;
   oldtype = __pthread_enable_asynccancel ();
-  int err = lll_futex_timed_wait_bitset (futex_word, expected, abstime,
-					 FUTEX_CLOCK_REALTIME, private);
+  int err = lll_futex_clock_wait_bitset (futex_word, expected,
+					clockid, abstime,
+					private);
   __pthread_disable_asynccancel (oldtype);
   switch (err)
     {
diff --git a/sysdeps/unix/sysv/linux/lowlevellock-futex.h b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
index 6f060b1..850a0fa 100644
--- a/sysdeps/unix/sysv/linux/lowlevellock-futex.h
+++ b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
@@ -82,12 +82,33 @@
 		     __lll_private_flag (FUTEX_WAIT, private),  \
 		     val, timeout)
 
-#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
-  lll_futex_syscall (6, futexp,                                         \
-		     __lll_private_flag (FUTEX_WAIT_BITSET | (clockbit), \
-					 private),                      \
-		     val, timeout, NULL /* Unused.  */,                 \
-		     FUTEX_BITSET_MATCH_ANY)
+/* Verify whether the supplied clockid is supported by
+   lll_futex_clock_wait_bitset */
+#define lll_futex_supported_clockid(clockid)			\
+  ((clockid) == CLOCK_REALTIME || (clockid) == CLOCK_MONOTONIC)
+
+/* The kernel currently only supports CLOCK_MONOTONIC or
+ * CLOCK_REALTIME timeouts for FUTEX_WAIT_BITSET. We could attempt to
+ * convert others here but currently do not.
+ */
+#define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
+  ({									\
+    long int __ret;							\
+    if (lll_futex_supported_clockid (clockid))                          \
+      {                                                                 \
+        const unsigned int clockbit =                                   \
+          (clockid == CLOCK_REALTIME) ? FUTEX_CLOCK_REALTIME : 0;       \
+        const int op =                                                  \
+          __lll_private_flag (FUTEX_WAIT_BITSET | clockbit, private);   \
+                                                                        \
+        __ret = lll_futex_syscall (6, futexp, op, val,                  \
+                                   timeout, NULL /* Unused.  */,	\
+                                   FUTEX_BITSET_MATCH_ANY);		\
+      }                                                                 \
+    else                                                                \
+      __ret = -EINVAL;							\
+    __ret;								\
+  })
 
 #define lll_futex_wake(futexp, nr, private)                             \
   lll_futex_syscall (4, futexp,                                         \
