Index: libc/gen/sem.c
===================================================================
RCS file: /cvs/FreeBSD/src/lib/libc/gen/sem.c,v
retrieving revision 1.15
diff -u -u -r1.15 sem.c
--- libc/gen/sem.c	18 Oct 2005 17:24:03 -0000	1.15
+++ libc/gen/sem.c	19 Feb 2006 17:48:17 -0000
@@ -59,6 +59,7 @@
 #include "namespace.h"
 #include <sys/types.h>
 #include <sys/queue.h>
+#include <sys/sysctl.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
@@ -70,6 +71,7 @@
 #include "un-namespace.h"
 #include "libc_private.h"
 
+static int   sem_supported = -1; /* changed by the first call to __sem_init() */
 static sem_t sem_alloc(unsigned int value, semid_t semid, int system_sem);
 static void  sem_free(sem_t sem);
 
@@ -140,6 +142,21 @@
 __sem_init(sem_t *sem, int pshared, unsigned int value)
 {
 	semid_t semid;
+	int mib[2];
+	size_t len;
+
+	if (sem_supported < 0) {
+		mib[0] = CTL_P1003_1B;
+		mib[1] = CTL_P1003_1B_SEMAPHORES;
+		len = sizeof(sem_supported);
+		if (sysctl(mib, 2, &sem_supported, &len, NULL, 0) < 0)
+			sem_supported = 0;
+	}
+
+	if (!sem_supported) {
+		errno = ENOSYS;
+		return -1;
+	}
 
 	/*
 	 * We always have to create the kernel semaphore if the
Index: libc/gen/sem_init.3
===================================================================
RCS file: /cvs/FreeBSD/src/lib/libc/gen/sem_init.3,v
retrieving revision 1.18
diff -u -u -r1.18 sem_init.3
--- libc/gen/sem_init.3	13 Jul 2005 13:15:21 -0000	1.18
+++ libc/gen/sem_init.3	19 Feb 2006 18:02:56 -0000
@@ -78,6 +78,10 @@
 .Dv SEM_VALUE_MAX .
 .It Bq Er ENOSPC
 Memory allocation error.
+.It Bq Er ENOSYS
+The system does not support
+.Tn POSIX
+semaphores.
 .It Bq Er EPERM
 Unable to initialize a shared semaphore.
 .El
@@ -94,6 +98,12 @@
 function conforms to
 .St -p1003.1-96 .
 .Pp
+Support for
+.Tn POSIX
+semaphores requires the currently running kernel to have been configured
+with
+.Cd "options P1003_1B_SEMAPHORES" .
+.Pp
 This implementation does not support shared semaphores, and reports this fact
 by setting
 .Va errno
Index: libthr/thread/thr_sem.c
===================================================================
RCS file: /cvs/FreeBSD/src/lib/libthr/thread/thr_sem.c,v
retrieving revision 1.6
diff -u -u -r1.6 thr_sem.c
--- libthr/thread/thr_sem.c	1 Sep 2005 15:21:23 -0000	1.6
+++ libthr/thread/thr_sem.c	19 Feb 2006 17:34:56 -0000
@@ -32,6 +32,7 @@
 
 #include "namespace.h"
 #include <sys/types.h>
+#include <sys/sysctl.h>
 #include <sys/queue.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -44,6 +45,7 @@
 
 #include "thr_private.h"
 
+static int   sem_supported = -1; /* changed by the first call to _sem_init() */
 
 __weak_reference(_sem_init, sem_init);
 __weak_reference(_sem_destroy, sem_destroy);
@@ -99,6 +101,21 @@
 _sem_init(sem_t *sem, int pshared, unsigned int value)
 {
 	semid_t semid;
+	int mib[2];
+	size_t len;
+
+	if (sem_supported < 0) {
+		mib[0] = CTL_P1003_1B;
+		mib[1] = CTL_P1003_1B_SEMAPHORES;
+		len = sizeof(sem_supported);
+		if (sysctl(mib, 2, &sem_supported, &len, NULL, 0) < 0)
+			sem_supported = 0;
+	}
+
+	if (!sem_supported) {
+		errno = ENOSYS;
+		return -1;
+	}
 
 	semid = (semid_t)SEM_USER;
 	if ((pshared != 0) && (ksem_init(&semid, value) != 0))
Index: libpthread/thread/thr_sem.c
===================================================================
RCS file: /cvs/FreeBSD/src/lib/libpthread/thread/thr_sem.c,v
retrieving revision 1.17
diff -u -u -r1.17 thr_sem.c
--- libpthread/thread/thr_sem.c	1 Sep 2005 15:16:46 -0000	1.17
+++ libpthread/thread/thr_sem.c	19 Feb 2006 17:44:36 -0000
@@ -31,6 +31,7 @@
 
 #include "namespace.h"
 #include <sys/types.h>
+#include <sys/sysctl.h>
 #include <sys/queue.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -43,7 +44,6 @@
 #include "libc_private.h"
 #include "thr_private.h"
 
-
 extern int pthread_cond_wait(pthread_cond_t *, pthread_mutex_t *);
 extern int pthread_cond_timedwait(pthread_cond_t *, pthread_mutex_t *,
 		struct timespec *);
@@ -53,6 +53,7 @@
 __weak_reference(_sem_timedwait, sem_timedwait);
 __weak_reference(_sem_post, sem_post);
 
+static int sem_supported = -1; /* changed by the first call to _sem_init() */
 
 static inline int
 sem_check_validity(sem_t *sem)
@@ -123,6 +124,21 @@
 _sem_init(sem_t *sem, int pshared, unsigned int value)
 {
 	semid_t semid;
+	int mib[2];
+	size_t len;
+
+	if (sem_supported < 0) {
+		mib[0] = CTL_P1003_1B;
+		mib[1] = CTL_P1003_1B_SEMAPHORES;
+		len = sizeof(sem_supported);
+		if (sysctl(mib, 2, &sem_supported, &len, NULL, 0) < 0)
+			sem_supported = 0;
+	}
+
+	if (!sem_supported) {
+		errno = ENOSYS;
+		return -1;
+	}
 
 	semid = (semid_t)SEM_USER;
 	if ((pshared != 0) && (ksem_init(&semid, value) != 0))