Disable -Wrestrict for two nptl/tst-attr3.c tests.

nptl/tst-attr3 fails to build with GCC mainline because of
(deliberate) aliasing between the second (attributes) and fourth
(argument to thread start routine) arguments to pthread_create.

Although both those arguments are restrict-qualified in POSIX,
pthread_create does not actually dereference its fourth argument; it's
an opaque pointer passed to the thread start routine.  Thus, the
aliasing is actually valid in this case, and it's deliberate in the
test.  So this patch makes the test disable -Wrestrict for the two
pthread_create calls in question.  (-Wrestrict was added in GCC 7,
hence the __GNUC_PREREQ conditions, but the particular warning in
question is new in GCC 8.)

Tested compilation with build-many-glibcs.py for aarch64-linux-gnu.

	* nptl/tst-attr3.c: Include <libc-diag.h>.
	(do_test) [__GNUC_PREREQ (7, 0)]: Ignore -Wrestrict for two tests.

(cherry picked from commit 40c4162df6766fb1e8ede875ca8df25d8075d3a5)

2 files changed, 24 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index d4223dbb9e..c6dfc5e677 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2017-12-18  Joseph Myers  <joseph@codesourcery.com>
+
+	* nptl/tst-attr3.c: Include <libc-diag.h>.
+	(do_test) [__GNUC_PREREQ (7, 0)]: Ignore -Wrestrict for two tests.
+
 2017-11-14  Joseph Myers  <joseph@codesourcery.com>
 
 	* string/bug-strncat1.c: Include <libc-diag.h>.
diff --git a/nptl/tst-attr3.c b/nptl/tst-attr3.c
index bc23386daf..420a7dba8b 100644
--- a/nptl/tst-attr3.c
+++ b/nptl/tst-attr3.c
@@ -26,6 +26,7 @@
 #include <unistd.h>
 
 #include <stackinfo.h>
+#include <libc-diag.h>
 
 static void *
 tf (void *arg)
@@ -362,7 +363,16 @@ do_test (void)
       result = 1;
     }
 
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 8 warns about aliasing of the restrict-qualified arguments
+     passed &a.  Since pthread_create does not dereference its fourth
+     argument, this aliasing, which is deliberate in this test, cannot
+     in fact cause problems.  */
+  DIAG_IGNORE_NEEDS_COMMENT (8, "-Wrestrict");
+#endif
   err = pthread_create (&th, &a, tf, &a);
+  DIAG_POP_NEEDS_COMMENT;
   if (err)
     {
       error (0, err, "pthread_create #2 failed");
@@ -388,7 +398,16 @@ do_test (void)
       result = 1;
     }
 
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 8 warns about aliasing of the restrict-qualified arguments
+     passed &a.  Since pthread_create does not dereference its fourth
+     argument, this aliasing, which is deliberate in this test, cannot
+     in fact cause problems.  */
+  DIAG_IGNORE_NEEDS_COMMENT (8, "-Wrestrict");
+#endif
   err = pthread_create (&th, &a, tf, &a);
+  DIAG_POP_NEEDS_COMMENT;
   if (err)
     {
       error (0, err, "pthread_create #3 failed");