nptl: Add C11 threads thrd_* functions

This patch adds the thrd_* definitions from C11 threads (ISO/IEC 9899:2011),
more specifically thrd_create, thrd_curent, rhd_detach, thrd_equal,
thrd_exit, thrd_join, thrd_sleep, thrd_yield, and required types.

Mostly of the definitions are composed based on POSIX conterparts, such as
thrd_t (using pthread_t).  For thrd_* function internally direct
POSIX pthread call are used with the exceptions:

  1. thrd_start uses pthread_create internal implementation, but changes
     how to actually calls the start routine.  This is due the difference
     in signature between POSIX and C11, where former return a 'void *'
     and latter 'int'.
     To avoid calling convention issues due 'void *' to int cast, routines
     from C11 threads are started slight different than default pthread one.
     Explicit cast to expected return are used internally on pthread_create
     and the result is stored back to void also with an explicit cast.

  2. thrd_sleep uses nanosleep internal direct syscall to avoid clobbering
     errno and to handle expected standard return codes.  It is a
     cancellation entrypoint to be consistent with both thrd_join and
     cnd_{timed}wait.

  3. thrd_yield also uses internal direct syscall to avoid errno clobbering.

Checked with a build for all major ABI (aarch64-linux-gnu, alpha-linux-gnu,
arm-linux-gnueabi, i386-linux-gnu, ia64-linux-gnu, m68k-linux-gnu,
microblaze-linux-gnu [1], mips{64}-linux-gnu, nios2-linux-gnu,
powerpc{64le}-linux-gnu, s390{x}-linux-gnu, sparc{64}-linux-gnu,
and x86_64-linux-gnu).

Also ran a full check on aarch64-linux-gnu, x86_64-linux-gnu, i686-linux-gnu,
arm-linux-gnueabhf, and powerpc64le-linux-gnu.

	[BZ #14092]
	* conform/Makefile (conformtest-headers-ISO11): Add threads.h.
	(linknamespace-libs-ISO11): Add libpthread.a.
	* conform/data/threads.h-data: New file: add C11 thrd_* types and
	functions.
	* include/stdc-predef.h (__STDC_NO_THREADS__): Remove definition.
	* nptl/Makefile (headers): Add threads.h.
	(libpthread-routines): Add new C11 thread thrd_create, thrd_current,
	thrd_detach, thrd_equal, thrd_exit, thrd_join, thrd_sleep, and
	thrd_yield.
	* nptl/Versions (libpthread) [GLIBC_2.28]): Add new C11 thread
	thrd_create, thrd_current, thrd_detach, thrd_equal, thrd_exit,
	thrd_join, thrd_sleep, and thrd_yield symbols.
	* nptl/descr.h (struct pthread): Add c11 field.
	* nptl/pthreadP.h (ATTR_C11_THREAD): New define.
	* nptl/pthread_create.c (START_THREAD_DEFN): Call C11 thread start
	routine with expected function prototype.
	(__pthread_create_2_1): Add C11 threads check based on attribute
	value.
	* sysdeps/unix/sysdep.h (INTERNAL_SYSCALL_CANCEL): New macro.
	* nptl/thrd_create.c: New file.
	* nptl/thrd_current.c: Likewise.
	* nptl/thrd_detach.c: Likewise.
	* nptl/thrd_equal.c: Likewise.
	* nptl/thrd_exit.c: Likewise.
	* nptl/thrd_join.c: Likewise.
	* nptl/thrd_priv.h: Likewise.
	* nptl/thrd_sleep.c: Likewise.
	* nptl/thrd_yield.c: Likewise.
	* include/threads.h: Likewise.

21 files changed, 478 insertions, 12 deletions

diff --git a/ChangeLog b/ChangeLog
index 8707c9c..5cafa4c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,36 @@
+2018-07-24  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
+
+	[BZ #14092]
+	* conform/Makefile (conformtest-headers-ISO11): Add threads.h.
+	(linknamespace-libs-ISO11): Add libpthread.a.
+	* conform/data/threads.h-data: New file: add C11 thrd_* types and
+	functions.
+	* include/stdc-predef.h (__STDC_NO_THREADS__): Remove definition.
+	* nptl/Makefile (headers): Add threads.h.
+	(libpthread-routines): Add new C11 thread thrd_create, thrd_current,
+	thrd_detach, thrd_equal, thrd_exit, thrd_join, thrd_sleep, and
+	thrd_yield.
+	* nptl/Versions (libpthread) [GLIBC_2.28]): Add new C11 thread
+	thrd_create, thrd_current, thrd_detach, thrd_equal, thrd_exit,
+	thrd_join, thrd_sleep, and thrd_yield symbols.
+	* nptl/descr.h (struct pthread): Add c11 field.
+	* nptl/pthreadP.h (ATTR_C11_THREAD): New define.
+	* nptl/pthread_create.c (START_THREAD_DEFN): Call C11 thread start
+	routine with expected function prototype.
+	(__pthread_create_2_1): Add C11 threads check based on attribute
+	value.
+	* sysdeps/unix/sysdep.h (INTERNAL_SYSCALL_CANCEL): New macro.
+	* nptl/thrd_create.c: New file.
+	* nptl/thrd_current.c: Likewise.
+	* nptl/thrd_detach.c: Likewise.
+	* nptl/thrd_equal.c: Likewise.
+	* nptl/thrd_exit.c: Likewise.
+	* nptl/thrd_join.c: Likewise.
+	* nptl/thrd_priv.h: Likewise.
+	* nptl/thrd_sleep.c: Likewise.
+	* nptl/thrd_yield.c: Likewise.
+	* include/threads.h: Likewise.
+
 2018-07-24  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* bits/indirect-return.h: New file.
diff --git a/conform/Makefile b/conform/Makefile
index 74fbda0..a0ab70e 100644
--- a/conform/Makefile
+++ b/conform/Makefile
@@ -34,9 +34,9 @@ conformtest-headers-ISO := assert.h ctype.h errno.h float.h limits.h locale.h \
 conformtest-headers-ISO99 := $(conformtest-headers-ISO) complex.h fenv.h \
 			     inttypes.h iso646.h stdbool.h stdint.h tgmath.h \
 			     wchar.h wctype.h
-# Missing ISO11 expectations for: stdatomic.h threads.h.
+# Missing ISO11 expectations for: stdatomic.h
 conformtest-headers-ISO11 := $(conformtest-headers-ISO99) stdalign.h \
-			     stdnoreturn.h uchar.h
+			     stdnoreturn.h threads.h uchar.h
 conformtest-headers-POSIX := $(conformtest-headers-ISO) aio.h dirent.h \
 			     fcntl.h fnmatch.h glob.h grp.h mqueue.h \
 			     pthread.h pwd.h regex.h sched.h semaphore.h \
@@ -196,8 +196,10 @@ linknamespace-libs-posix = $(linknamespace-libs-thr) \
 linknamespace-libs-xsi = $(linknamespace-libs-posix)
 linknamespace-libs-ISO = $(linknamespace-libs-isoc)
 linknamespace-libs-ISO99 = $(linknamespace-libs-isoc)
-linknamespace-libs-ISO11 = $(linknamespace-libs-isoc)
-linknamespace-libs-XPG4 = $(linknamespace-libs-isoc)
+linknamespace-libs-ISO11 = $(linknamespace-libs-isoc) \
+			   $(common-objpfx)nptl/libpthread.a
+linknamespace-libs-XPG4 = $(linknamespace-libs-isoc) \
+			  $(common-objpfx)crypt/libcrypt.a
 linknamespace-libs-XPG42 = $(linknamespace-libs-XPG4)
 linknamespace-libs-POSIX = $(linknamespace-libs-thr)
 linknamespace-libs-UNIX98 = $(linknamespace-libs-xsi)
diff --git a/conform/data/threads.h-data b/conform/data/threads.h-data
new file mode 100644
index 0000000..bc2d857
--- /dev/null
+++ b/conform/data/threads.h-data
@@ -0,0 +1,23 @@
+#if defined ISO11
+
+constant thrd_success
+constant thrd_busy
+constant thrd_error
+constant thrd_nomem
+constant thrd_timedout
+
+type thrd_t
+type thrd_start_t
+
+function int thrd_create (thrd_t*, thrd_start_t, void*)
+function int thrd_equal (thrd_t, thrd_t)
+function thrd_t thrd_current (void)
+function int thrd_sleep (const struct timespec*, struct timespec*)
+function void thrd_exit (int)
+function int thrd_detach (thrd_t)
+function int thrd_join (thrd_t, int*)
+function void thrd_yield (void)
+
+#include "time.h-data"
+
+#endif
diff --git a/include/stdc-predef.h b/include/stdc-predef.h
index c569759..c2ab78a 100644
--- a/include/stdc-predef.h
+++ b/include/stdc-predef.h
@@ -57,7 +57,4 @@
    - 3 additional Zanabazar Square characters */
 #define __STDC_ISO_10646__		201706L
 
-/* We do not support C11 <threads.h>.  */
-#define __STDC_NO_THREADS__		1
-
 #endif
diff --git a/include/threads.h b/include/threads.h
new file mode 100644
index 0000000..1090612
--- /dev/null
+++ b/include/threads.h
@@ -0,0 +1 @@
+#include <nptl/threads.h>
diff --git a/nptl/Makefile b/nptl/Makefile
index 2f2bb05..1fcf29f 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -22,14 +22,15 @@ subdir	:= nptl
 
 include ../Makeconfig
 
-headers := pthread.h semaphore.h bits/semaphore.h
+headers := pthread.h semaphore.h bits/semaphore.h threads.h
 
 extra-libs := libpthread
 extra-libs-others := $(extra-libs)
 
 routines = alloca_cutoff forward libc-lowlevellock libc-cancellation \
 	   libc-cleanup libc_pthread_init libc_multiple_threads \
-	   register-atfork pthread_atfork pthread_self
+	   register-atfork pthread_atfork pthread_self thrd_current \
+	   thrd_equal thrd_sleep thrd_yield
 shared-only-routines = forward
 static-only-routines = pthread_atfork
 
@@ -139,7 +140,8 @@ libpthread-routines = nptl-init nptlfreeres vars events version pt-interp \
 		      pthread_mutex_getprioceiling \
 		      pthread_mutex_setprioceiling \
 		      pthread_setname pthread_getname \
-		      pthread_setattr_default_np pthread_getattr_default_np
+		      pthread_setattr_default_np pthread_getattr_default_np \
+		      thrd_create thrd_detach thrd_exit thrd_join
 #		      pthread_setuid pthread_seteuid pthread_setreuid \
 #		      pthread_setresuid \
 #		      pthread_setgid pthread_setegid pthread_setregid \
diff --git a/nptl/Versions b/nptl/Versions
index b1c2da0..38d7e48 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -28,6 +28,10 @@ libc {
     pthread_cond_wait; pthread_cond_signal;
     pthread_cond_broadcast; pthread_cond_timedwait;
   }
+  # C11 thread symbols.
+  GLIBC_2.28 {
+    thrd_current; thrd_equal; thrd_sleep; thrd_yield;
+  }
   GLIBC_PRIVATE {
     __libc_alloca_cutoff;
     # Internal libc interface to libpthread
@@ -265,6 +269,11 @@ libpthread {
   GLIBC_2.22 {
   }
 
+  # C11 thread symbols.
+  GLIBC_2.28 {
+    thrd_create; thrd_detach; thrd_exit; thrd_join;
+  }
+
   GLIBC_PRIVATE {
     __pthread_initialize_minimal;
     __pthread_clock_gettime; __pthread_clock_settime;
diff --git a/nptl/descr.h b/nptl/descr.h
index 0a0abb4..9c01e1b 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -392,6 +392,9 @@ struct pthread
   /* Resolver state.  */
   struct __res_state res;
 
+  /* Indicates whether is a C11 thread created by thrd_creat.  */
+  bool c11;
+
   /* This member must be last.  */
   char end_padding[];
 
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 3cba0b6..13bdb11 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -173,6 +173,9 @@ enum
 #define __PTHREAD_ONCE_DONE		2
 #define __PTHREAD_ONCE_FORK_GEN_INCR	4
 
+/* Attribute to indicate thread creation was issued from C11 thrd_create.  */
+#define ATTR_C11_THREAD ((void*)(uintptr_t)-1)
+
 
 /* Condition variable definitions.  See __pthread_cond_wait_common.
    Need to be defined here so there is one place from which
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index 5f5a007..fe75d04 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -472,7 +472,19 @@ START_THREAD_DEFN
       LIBC_PROBE (pthread_start, 3, (pthread_t) pd, pd->start_routine, pd->arg);
 
       /* Run the code the user provided.  */
-      THREAD_SETMEM (pd, result, pd->start_routine (pd->arg));
+      void *ret;
+      if (pd->c11)
+	{
+	  /* The function pointer of the c11 thread start is cast to an incorrect
+	     type on __pthread_create_2_1 call, however it is casted back to correct
+	     one so the call behavior is well-defined (it is assumed that pointers
+	     to void are able to represent all values of int.  */
+	  int (*start)(void*) = (int (*) (void*)) pd->start_routine;
+	  ret = (void*) (uintptr_t) start (pd->arg);
+	}
+      else
+	ret = pd->start_routine (pd->arg);
+      THREAD_SETMEM (pd, result, ret);
     }
 
   /* Call destructors for the thread_local TLS variables.  */
@@ -625,7 +637,8 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
   const struct pthread_attr *iattr = (struct pthread_attr *) attr;
   struct pthread_attr default_attr;
   bool free_cpuset = false;
-  if (iattr == NULL)
+  bool c11 = (attr == ATTR_C11_THREAD);
+  if (iattr == NULL || c11)
     {
       lll_lock (__default_pthread_attr_lock, LLL_PRIVATE);
       default_attr = __default_pthread_attr;
@@ -683,6 +696,7 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
      get the information from its thread descriptor.  */
   pd->start_routine = start_routine;
   pd->arg = arg;
+  pd->c11 = c11;
 
   /* Copy the thread attribute flags.  */
   struct pthread *self = THREAD_SELF;
diff --git a/nptl/thrd_create.c b/nptl/thrd_create.c
new file mode 100644
index 0000000..113ba0d
--- /dev/null
+++ b/nptl/thrd_create.c
@@ -0,0 +1,30 @@
+/* C11 threads thread creation implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+int
+thrd_create (thrd_t *thr, thrd_start_t func, void *arg)
+{
+  _Static_assert (sizeof (thr) == sizeof (pthread_t),
+		  "sizeof (thr) != sizeof (pthread_t)");
+
+  int err_code = __pthread_create_2_1 (thr, ATTR_C11_THREAD,
+				       (void* (*) (void*))func, arg);
+  return thrd_err_map (err_code);
+}
diff --git a/nptl/thrd_current.c b/nptl/thrd_current.c
new file mode 100644
index 0000000..a1c73b2
--- /dev/null
+++ b/nptl/thrd_current.c
@@ -0,0 +1,25 @@
+/* C11 threads current thread implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+thrd_t
+thrd_current (void)
+{
+  return (thrd_t) THREAD_SELF;
+}
diff --git a/nptl/thrd_detach.c b/nptl/thrd_detach.c
new file mode 100644
index 0000000..be2c3e1
--- /dev/null
+++ b/nptl/thrd_detach.c
@@ -0,0 +1,28 @@
+/* C11 threads thread detach implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+int
+thrd_detach (thrd_t thr)
+{
+  int err_code;
+
+  err_code = __pthread_detach (thr);
+  return thrd_err_map (err_code);
+}
diff --git a/nptl/thrd_equal.c b/nptl/thrd_equal.c
new file mode 100644
index 0000000..8e13bc4
--- /dev/null
+++ b/nptl/thrd_equal.c
@@ -0,0 +1,25 @@
+/* C11 threads thread equality check implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+int
+thrd_equal (thrd_t lhs, thrd_t rhs)
+{
+  return lhs == rhs;
+}
diff --git a/nptl/thrd_exit.c b/nptl/thrd_exit.c
new file mode 100644
index 0000000..6b37774
--- /dev/null
+++ b/nptl/thrd_exit.c
@@ -0,0 +1,25 @@
+/* C11 threads thread exit implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+_Noreturn void
+thrd_exit (int res)
+{
+  __pthread_exit ((void*)(uintptr_t) res);
+}
diff --git a/nptl/thrd_join.c b/nptl/thrd_join.c
new file mode 100644
index 0000000..029d4a7
--- /dev/null
+++ b/nptl/thrd_join.c
@@ -0,0 +1,30 @@
+/* C11 threads thread join implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+int
+thrd_join (thrd_t thr, int *res)
+{
+  void *pthread_res;
+  int err_code = __pthread_timedjoin_ex (thr, &pthread_res, NULL, true);
+  if (res)
+   *res = (int) (uintptr_t) pthread_res;
+
+  return thrd_err_map (err_code);
+}
diff --git a/nptl/thrd_priv.h b/nptl/thrd_priv.h
new file mode 100644
index 0000000..97f4102
--- /dev/null
+++ b/nptl/thrd_priv.h
@@ -0,0 +1,45 @@
+/* Internal C11 threads definitions.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef THRD_PRIV_H
+# define THRD_PRIV_H
+
+#include <features.h>
+#include <threads.h>
+#include <errno.h>
+#include "pthreadP.h"	/* For pthread_{mutex,cond}_t definitions.  */
+
+static __always_inline int
+thrd_err_map (int err_code)
+{
+  switch (err_code)
+  {
+    case 0:
+      return thrd_success;
+    case ENOMEM:
+      return thrd_nomem;
+    case ETIMEDOUT:
+      return thrd_timedout;
+    case EBUSY:
+      return thrd_busy;
+    default:
+      return thrd_error;
+  }
+}
+
+#endif
diff --git a/nptl/thrd_sleep.c b/nptl/thrd_sleep.c
new file mode 100644
index 0000000..85736ed
--- /dev/null
+++ b/nptl/thrd_sleep.c
@@ -0,0 +1,39 @@
+/* C11 threads thread sleep implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <time.h>
+#include <sysdep-cancel.h>
+
+#include "thrd_priv.h"
+
+int
+thrd_sleep (const struct timespec* time_point, struct timespec* remaining)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  int ret = INTERNAL_SYSCALL_CANCEL (nanosleep, err, time_point, remaining);
+  if (INTERNAL_SYSCALL_ERROR_P (ret, err))
+    {
+      /* C11 states thrd_sleep function returns -1 if it has been interrupted
+	 by a signal, or a negative value if it fails.  */
+      ret = INTERNAL_SYSCALL_ERRNO (ret, err);
+      if (ret == EINTR)
+	return -1;
+      return -2;
+    }
+  return 0;
+}
diff --git a/nptl/thrd_yield.c b/nptl/thrd_yield.c
new file mode 100644
index 0000000..9ebcbae
--- /dev/null
+++ b/nptl/thrd_yield.c
@@ -0,0 +1,26 @@
+/* C11 threads thread yield implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+void
+thrd_yield (void)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  INTERNAL_SYSCALL_CALL (sched_yield, err);
+}
diff --git a/nptl/threads.h b/nptl/threads.h
new file mode 100644
index 0000000..5258e23
--- /dev/null
+++ b/nptl/threads.h
@@ -0,0 +1,90 @@
+/* ISO C11 Standard: 7.26 - Thread support library  <threads.h>.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _THREADS_H
+#define _THREADS_H	1
+
+#include <features.h>
+#include <time.h>
+
+__BEGIN_DECLS
+
+#include <bits/types/struct_timespec.h>
+
+typedef unsigned long int thrd_t;
+typedef int (*thrd_start_t) (void*);
+
+/* Exit and error codes.  */
+enum
+{
+  thrd_success  = 0,
+  thrd_busy     = 1,
+  thrd_error    = 2,
+  thrd_nomem    = 3,
+  thrd_timedout = 4
+};
+
+/* Threads functions.  */
+
+/* Create a new thread executing the function __FUNC.  Arguments for __FUNC
+   are passed through __ARG.  If succesful, __THR is set to new thread
+   identifier.  */
+extern int thrd_create (thrd_t *__thr, thrd_start_t __func, void *__arg);
+
+/* Check if __LHS and __RHS point to the same thread.  */
+extern int thrd_equal (thrd_t __lhs, thrd_t __rhs);
+
+/* Return current thread identifier.  */
+extern thrd_t thrd_current (void);
+
+/* Block current thread execution for at least the time pointed by
+   __TIME_POINT.  The current thread may resume if receives a signal.  In
+   that case, if __REMAINING is not NULL, the remaining time is stored in
+   the object pointed by it.  */
+extern int thrd_sleep (const struct timespec *__time_point,
+		       struct timespec *__remaining);
+
+/* Terminate current thread execution, cleaning up any thread local
+   storage and freeing resources.  Returns the value specified in __RES.  */
+extern void thrd_exit (int __res) __attribute__ ((__noreturn__));
+
+/* Detach the thread identified by __THR from the current environment
+   (it does not allow join or wait for it).  */
+extern int thrd_detach (thrd_t __thr);
+
+/* Block current thread until execution of __THR is complete.  In case that
+   __RES is not NULL, will store the return value of __THR when exiting.  */
+extern int thrd_join (thrd_t __thr, int *__res);
+
+/* Stop current thread execution and call the scheduler to decide which
+   thread should execute next.  The current thread may be selected by the
+   scheduler to keep running.  */
+extern void thrd_yield (void);
+
+#ifdef __USE_EXTERN_INLINES
+/* Optimizations.  */
+__extern_inline int
+thrd_equal (thrd_t __thread1, thrd_t __thread2)
+{
+  return __thread1 == __thread2;
+}
+#endif
+
+__END_DECLS
+
+#endif /* _THREADS_H */
diff --git a/sysdeps/unix/sysdep.h b/sysdeps/unix/sysdep.h
index aac9303..29c3961 100644
--- a/sysdeps/unix/sysdep.h
+++ b/sysdeps/unix/sysdep.h
@@ -102,6 +102,22 @@
     sc_ret;								     \
   })
 
+/* Issue a syscall defined by syscall number plus any other argument
+   required.  Any error will be returned unmodified (including errno).  */
+#define INTERNAL_SYSCALL_CANCEL(...) \
+  ({									     \
+    long int sc_ret;							     \
+    if (SINGLE_THREAD_P) 						     \
+      sc_ret = INTERNAL_SYSCALL_CALL (__VA_ARGS__); 			     \
+    else								     \
+      {									     \
+	int sc_cancel_oldtype = LIBC_CANCEL_ASYNC ();			     \
+	sc_ret = INTERNAL_SYSCALL_CALL (__VA_ARGS__);			     \
+        LIBC_CANCEL_RESET (sc_cancel_oldtype);				     \
+      }									     \
+    sc_ret;								     \
+  })
+
 /* Machine-dependent sysdep.h files are expected to define the macro
    PSEUDO (function_name, syscall_name) to emit assembly code to define the
    C-callable function FUNCTION_NAME to do system call SYSCALL_NAME.