--- a/ChangeLog	Fri Jul 13 11:54:21 2012 +0100
+++ b/ChangeLog	Sun Jul 15 11:06:11 2012 -0700
@@ -1,3 +1,16 @@
+2012-07-15  Paul Eggert  <eggert@cs.ucla.edu>
+
+	pthread_sigmask: fix bug on FreeBSD 9
+	* lib/pthread_sigmask.c [PTHREAD_SIGMASK_INEFFECTIVE]:
+	Include string.h.
+	(pthread_sigmask) [PTHREAD_SIGMASK_INEFFECTIVE]:
+	When calling pthread_sigmask (1729, NEW, OLD), specify non-null NEW;
+	this avoids a bug on FreeBSD 9, where pthread_sigmask is effective
+	but pthread_sigmask (1729, NULL, NULL) returns zero.
+	See <http://bugs.gnu.org/11884>.
+	Avoid the need to call pthread_sigmask (1729, ...) in most cases,
+	by inspecting whether the main call changed the old mask.
+
 2012-07-15  Reuben Thomas  <rrt@sc3d.org>
 
 	README-release: make it more legible

--- a/lib/pthread_sigmask.c	Fri Jul 13 11:54:21 2012 +0100
+++ b/lib/pthread_sigmask.c	Sun Jul 15 11:06:11 2012 -0700
@@ -22,6 +22,10 @@
 #include <errno.h>
 #include <stddef.h>
 
+#if PTHREAD_SIGMASK_INEFFECTIVE
+# include <string.h>
+#endif
+
 #if PTHREAD_SIGMASK_UNBLOCK_BUG
 # include <unistd.h>
 #endif
@@ -31,7 +35,22 @@
 #undef pthread_sigmask
 {
 #if HAVE_PTHREAD_SIGMASK
-  int ret = pthread_sigmask (how, new_mask, old_mask);
+  int ret;
+
+# if PTHREAD_SIGMASK_INEFFECTIVE
+  sigset_t omask, omask_copy;
+  sigset_t *old_mask_ptr = &omask;
+  sigemptyset (&omask);
+  /* Add a signal unlikely to be blocked, so that OMASK_COPY
+     is unlikely to match the actual mask.  */
+  sigaddset (&omask, SIGILL);
+  memcpy (&omask_copy, &omask, sizeof omask);
+# else
+  sigset_t *old_mask_ptr = old_mask;
+# endif
+
+  ret = pthread_sigmask (how, new_mask, old_mask_ptr);
+
 # if PTHREAD_SIGMASK_INEFFECTIVE
   if (ret == 0)
     {
@@ -39,12 +58,16 @@
          Don't cache the information: libpthread.so could be dynamically
          loaded after the program started and after pthread_sigmask was
          called for the first time.  */
-      if (pthread_sigmask (1729, NULL, NULL) == 0)
+      if (memcmp (&omask_copy, &omask, sizeof omask) == 0
+          && pthread_sigmask (1729, &omask_copy, NULL) == 0)
         {
           /* pthread_sigmask is currently ineffective.  The program is not
              linked to -lpthread.  So use sigprocmask instead.  */
           return (sigprocmask (how, new_mask, old_mask) < 0 ? errno : 0);
         }
+
+      if (old_mask)
+        memcpy (old_mask, &omask, sizeof omask);
     }
 # endif
 # if PTHREAD_SIGMASK_FAILS_WITH_ERRNO