New test case to verify padding usage.

diff --git a/nptl/Makefile b/nptl/Makefile
index ff4d590f11c38277..9a56d34313d06444 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -319,6 +319,8 @@ tests-internal := tst-robustpi8 tst-rwlock19 tst-rwlock20 \
 		  tst-barrier5 tst-signal7 tst-mutex8 tst-mutex8-static \
 		  tst-mutexpi8 tst-mutexpi8-static \
 		  tst-setgetname \
+		  tst-nptl-padding \
+		  # tests-internal
 
 xtests = tst-setuid1 tst-setuid1-static tst-setuid2 \
 	tst-mutexpp1 tst-mutexpp6 tst-mutexpp10 tst-setgroups \
diff --git a/nptl/tst-nptl-padding.c b/nptl/tst-nptl-padding.c
new file mode 100644
index 0000000000000000..5bb64f4a54335e36
--- /dev/null
+++ b/nptl/tst-nptl-padding.c
@@ -0,0 +1,57 @@
+/* Downstream-only test for verifying that fields that have been
+   relocated into struct pthread padding actually use the padding.
+
+   At present, only rtld_catch (downstream: rtld_catch_f) has been
+   placed into padding.  */
+
+#include <descr.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  struct pthread descr;
+
+  /* Mark the entire descriptor as used.  */
+  memset (&descr, 0xff, sizeof (descr));
+
+  /* Mark the padding as unused.  */
+#ifdef __x86_64__
+  /* Special case: Usable padding is in the header.   */
+  memset (&descr.header.__padding, 0, sizeof (descr.header.__padding));
+#else
+  /* The padding should be directly adjacent to the first real
+     struct field.  */
+  TEST_COMPARE (sizeof (descr.__padding), offsetof (struct pthread, list));
+
+  /* Clear the unused tail of the padding.  */
+  {
+    char *base = (char *) &descr;
+    char *end_of_header = base + sizeof (descr.header);
+    char *end_of_padding = base + sizeof (descr.__padding);
+    memset (end_of_header, 0, end_of_padding - end_of_header);
+  }
+#endif
+
+  /* These fields are not in padding and should remain marked as used.   */
+  TEST_COMPARE (descr.header.gscope_flag, -1);
+  TEST_COMPARE ((intptr_t) descr.list.next, -1);
+  TEST_COMPARE ((intptr_t) descr.list.prev, -1);
+
+  /* But this field remains in padding.  */
+  TEST_COMPARE ((intptr_t) descr.rtld_catch_f, 0);
+
+  /* Write to all padding-relocated fields below to show that they
+     have independent locations.  */
+  struct rtld_catch *rtld_catch_dummy = (void *) "rtld_catch_dummy";
+  descr.rtld_catch_f = rtld_catch_dummy;
+
+  TEST_VERIFY (descr.rtld_catch_f == rtld_catch_dummy);
+
+  return 0;
+}
+
+#include <support/test-driver.c>