[COMMITTED PATCH] NPTL: Conditionalize direct futex syscall uses.

[Roland McGrath <roland at hack dot frob dot com>]

This has no material effect on Linux configurations.


Thanks,
Roland


	* nptl/nptl-init.c (__pthread_initialize_minimal_internal):
	Conditionalize FUTEX_PRIVATE_FLAG and FUTEX_CLOCK_REALTIME probes
	on [__NR_futex].
	* nptl/pthread_mutex_init.c (prio_inherit_missing): New function,
	broken out of ...
	(__pthread_mutex_init): ... here.  Call it.
	* nptl/pthread_mutex_lock.c (__pthread_mutex_lock_full):
	Conditionalize PI cases on [__NR_futex].
	* nptl/pthread_mutex_timedlock.c (pthread_mutex_timedlock): Likewise.
	* nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock): Likewise.
	* nptl/pthread_mutex_unlock.c (__pthread_mutex_unlock_full): Likewise.

--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -329,7 +329,8 @@ __pthread_initialize_minimal_internal (void)
 #endif
     set_robust_list_not_avail ();
 
-#ifndef __ASSUME_PRIVATE_FUTEX
+#ifdef __NR_futex
+# ifndef __ASSUME_PRIVATE_FUTEX
   /* Private futexes are always used (at least internally) so that
      doing the test once this early is beneficial.  */
   {
@@ -345,8 +346,8 @@ __pthread_initialize_minimal_internal (void)
      know the former are not supported.  This also means we know the
      kernel will return ENOSYS for unknown operations.  */
   if (THREAD_GETMEM (pd, header.private_futex) != 0)
-#endif
-#ifndef __ASSUME_FUTEX_CLOCK_REALTIME
+# endif
+# ifndef __ASSUME_FUTEX_CLOCK_REALTIME
     {
       int word = 0;
       /* NB: the syscall actually takes six parameters.  The last is the
@@ -361,6 +362,7 @@ __pthread_initialize_minimal_internal (void)
       if (INTERNAL_SYSCALL_ERRNO (word, err) != ENOSYS)
 	__set_futex_clock_realtime ();
     }
+# endif
 #endif
 
   /* Set initial thread's stack block from 0 up to __libc_stack_end.
--- a/nptl/pthread_mutex_init.c
+++ b/nptl/pthread_mutex_init.c
@@ -18,6 +18,7 @@
 
 #include <assert.h>
 #include <errno.h>
+#include <stdbool.h>
 #include <string.h>
 #include <kernel-features.h>
 #include "pthreadP.h"
@@ -31,10 +32,26 @@ static const struct pthread_mutexattr default_mutexattr =
   };
 
 
-#ifndef __ASSUME_FUTEX_LOCK_PI
-static int tpi_supported;
+static bool
+prio_inherit_missing (void)
+{
+#ifdef __NR_futex
+# ifndef __ASSUME_FUTEX_LOCK_PI
+  static int tpi_supported;
+  if (__glibc_unlikely (tpi_supported == 0))
+    {
+      int lock = 0;
+      INTERNAL_SYSCALL_DECL (err);
+      int ret = INTERNAL_SYSCALL (futex, err, 4, &lock, FUTEX_UNLOCK_PI, 0, 0);
+      assert (INTERNAL_SYSCALL_ERROR_P (ret, err));
+      tpi_supported = INTERNAL_SYSCALL_ERRNO (ret, err) == ENOSYS ? -1 : 1;
+    }
+  return __glibc_unlikely (tpi_supported < 0);
+# endif
+  return false;
 #endif
-
+  return true;
+}
 
 int
 __pthread_mutex_init (mutex, mutexattr)
@@ -58,19 +75,8 @@ __pthread_mutex_init (mutex, mutexattr)
       break;
 
     case PTHREAD_PRIO_INHERIT << PTHREAD_MUTEXATTR_PROTOCOL_SHIFT:
-#ifndef __ASSUME_FUTEX_LOCK_PI
-      if (__glibc_unlikely (tpi_supported == 0))
-	{
-	  int lock = 0;
-	  INTERNAL_SYSCALL_DECL (err);
-	  int ret = INTERNAL_SYSCALL (futex, err, 4, &lock, FUTEX_UNLOCK_PI,
-				      0, 0);
-	  assert (INTERNAL_SYSCALL_ERROR_P (ret, err));
-	  tpi_supported = INTERNAL_SYSCALL_ERRNO (ret, err) == ENOSYS ? -1 : 1;
-	}
-      if (__glibc_unlikely (tpi_supported < 0))
+      if (__glibc_unlikely (prio_inherit_missing ()))
 	return ENOTSUP;
-#endif
       break;
 
     default:
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -276,6 +276,10 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
       break;
 
+    /* The PI support requires the Linux futex system call.  If that's not
+       available, pthread_mutex_init should never have allowed the type to
+       be set.  So it will get the default case for an invalid type.  */
+#ifdef __NR_futex
     case PTHREAD_MUTEX_PI_RECURSIVE_NP:
     case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
     case PTHREAD_MUTEX_PI_NORMAL_NP:
@@ -321,9 +325,9 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	  }
 
 	int newval = id;
-#ifdef NO_INCR
+# ifdef NO_INCR
 	newval |= FUTEX_WAITERS;
-#endif
+# endif
 	oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
 						      newval, 0);
 
@@ -377,9 +381,9 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	       incremented which is not correct because the old owner
 	       has to be discounted.  If we are not supposed to
 	       increment __nusers we actually have to decrement it here.  */
-#ifdef NO_INCR
+# ifdef NO_INCR
 	    --mutex->__data.__nusers;
-#endif
+# endif
 
 	    return EOWNERDEAD;
 	  }
@@ -409,6 +413,7 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	  }
       }
       break;
+#endif  /* __NR_futex.  */
 
     case PTHREAD_MUTEX_PP_RECURSIVE_NP:
     case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -230,6 +230,10 @@ pthread_mutex_timedlock (mutex, abstime)
       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
       break;
 
+    /* The PI support requires the Linux futex system call.  If that's not
+       available, pthread_mutex_init should never have allowed the type to
+       be set.  So it will get the default case for an invalid type.  */
+#ifdef __NR_futex
     case PTHREAD_MUTEX_PI_RECURSIVE_NP:
     case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
     case PTHREAD_MUTEX_PI_NORMAL_NP:
@@ -382,6 +386,7 @@ pthread_mutex_timedlock (mutex, abstime)
 	  }
 	}
       break;
+#endif  /* __NR_futex.  */
 
     case PTHREAD_MUTEX_PP_RECURSIVE_NP:
     case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
--- a/nptl/pthread_mutex_trylock.c
+++ b/nptl/pthread_mutex_trylock.c
@@ -191,6 +191,10 @@ __pthread_mutex_trylock (mutex)
 
       return 0;
 
+    /* The PI support requires the Linux futex system call.  If that's not
+       available, pthread_mutex_init should never have allowed the type to
+       be set.  So it will get the default case for an invalid type.  */
+#ifdef __NR_futex
     case PTHREAD_MUTEX_PI_RECURSIVE_NP:
     case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
     case PTHREAD_MUTEX_PI_NORMAL_NP:
@@ -319,6 +323,7 @@ __pthread_mutex_trylock (mutex)
 
 	return 0;
       }
+#endif  /* __NR_futex.  */
 
     case PTHREAD_MUTEX_PP_RECURSIVE_NP:
     case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
--- a/nptl/pthread_mutex_unlock.c
+++ b/nptl/pthread_mutex_unlock.c
@@ -158,6 +158,10 @@ __pthread_mutex_unlock_full (pthread_mutex_t *mutex, int decr)
       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
       break;
 
+    /* The PI support requires the Linux futex system call.  If that's not
+       available, pthread_mutex_init should never have allowed the type to
+       be set.  So it will get the default case for an invalid type.  */
+#ifdef __NR_futex
     case PTHREAD_MUTEX_PI_RECURSIVE_NP:
       /* Recursive mutex.  */
       if (mutex->__data.__owner != THREAD_GETMEM (THREAD_SELF, tid))
@@ -245,6 +249,7 @@ __pthread_mutex_unlock_full (pthread_mutex_t *mutex, int decr)
 
       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
       break;
+#endif  /* __NR_futex.  */
 
     case PTHREAD_MUTEX_PP_RECURSIVE_NP:
       /* Recursive mutex.  */