diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 44ace04..4f40ea8 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,14 @@
+2019-11-12  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdbsupport/format.c (format_pieces::format_pieces): Support
+	printf 'z' size modifier.
+	* gdbsupport/format.h (enum argclass): Add size_t_arg.
+	* printcmd.c (ui_printf):  Handle size_t_arg.
+	* ui-out.c (ui_out::vmessage): Likewise.
+	* unittests/format_pieces-selftests.c (test_format_int_sizes): New
+	function.
+	(run_tests): Call test_format_int_sizes.
+
 2019-11-12  Christian Biesinger  <cbiesinger@google.com>
 
 	* ada-exp.y (write_ambiguous_var): Update.
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 9d0afaa..e17a7ca 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,7 @@
+2019-11-12  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* ax.c (ax_printf): Handle size_t_arg.
+
 2019-11-06  Christian Biesinger  <cbiesinger@google.com>
 
 	* linux-tdep.c (linux_info_proc): Use strtok_r instead of strtok.
diff --git a/gdb/gdbserver/ax.c b/gdb/gdbserver/ax.c
index 2c096ef..21fde5e 100644
--- a/gdb/gdbserver/ax.c
+++ b/gdb/gdbserver/ax.c
@@ -904,6 +904,14 @@
 	    break;
 	  }
 
+	case size_t_arg:
+	  {
+	    size_t val = args[i];
+
+	    printf (current_substring, val);
+	    break;
+	  }
+
 	case literal_piece:
 	  /* Print a portion of the format string that has no
 	     directives.  Note that this will not include any
diff --git a/gdb/gdbsupport/format.c b/gdb/gdbsupport/format.c
index 1e80350..2e2d90a 100644
--- a/gdb/gdbsupport/format.c
+++ b/gdb/gdbsupport/format.c
@@ -123,6 +123,7 @@
 	int seen_space = 0, seen_plus = 0;
 	int seen_big_l = 0, seen_h = 0, seen_big_h = 0;
 	int seen_big_d = 0, seen_double_big_d = 0;
+	int seen_size_t = 0;
 	int bad = 0;
 	int n_int_args = 0;
 
@@ -234,6 +235,12 @@
 	    else
 	      seen_big_d = 1;
 	  }
+	/* For size_t or ssize_t.  */
+	else if (*f == 'z')
+	  {
+	    seen_size_t = 1;
+	    f++;
+	  }
 
 	switch (*f)
 	  {
@@ -251,7 +258,9 @@
 
 	  case 'd':
 	  case 'i':
-	    if (lcount == 0)
+	    if (seen_size_t)
+	      this_argclass = size_t_arg;
+	    else if (lcount == 0)
 	      this_argclass = int_arg;
 	    else if (lcount == 1)
 	      this_argclass = long_arg;
diff --git a/gdb/gdbsupport/format.h b/gdb/gdbsupport/format.h
index e2a47ba..07374db 100644
--- a/gdb/gdbsupport/format.h
+++ b/gdb/gdbsupport/format.h
@@ -38,7 +38,7 @@
 enum argclass
   {
     literal_piece,
-    int_arg, long_arg, long_long_arg, ptr_arg,
+    int_arg, long_arg, long_long_arg, size_t_arg, ptr_arg,
     string_arg, wide_string_arg, wide_char_arg,
     double_arg, long_double_arg,
     dec32float_arg, dec64float_arg, dec128float_arg
diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index 27aaf7a..323a5d0 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -2663,6 +2663,16 @@
 	      DIAGNOSTIC_POP
 	      break;
 	    }
+	  case size_t_arg:
+	    {
+	      size_t val = value_as_long (val_args[i]);
+
+	      DIAGNOSTIC_PUSH
+	      DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL
+              fprintf_filtered (stream, current_substring, val);
+	      DIAGNOSTIC_POP
+	      break;
+	    }
 	  /* Handles floating-point values.  */
 	  case double_arg:
 	  case long_double_arg:
diff --git a/gdb/ui-out.c b/gdb/ui-out.c
index 6b0b5ac..80845f4 100644
--- a/gdb/ui-out.c
+++ b/gdb/ui-out.c
@@ -688,6 +688,24 @@
 	      }
 	  }
 	  break;
+	case size_t_arg:
+	  {
+	    size_t val = va_arg (args, size_t);
+	    switch (piece.n_int_args)
+	      {
+	      case 0:
+		call_do_message (style, current_substring, val);
+		break;
+	      case 1:
+		call_do_message (style, current_substring, intvals[0], val);
+		break;
+	      case 2:
+		call_do_message (style, current_substring,
+				 intvals[0], intvals[1], val);
+		break;
+	      }
+	  }
+	  break;
 	case double_arg:
 	  call_do_message (style, current_substring, va_arg (args, double));
 	  break;
diff --git a/gdb/unittests/format_pieces-selftests.c b/gdb/unittests/format_pieces-selftests.c
index ed83d96..3971201 100644
--- a/gdb/unittests/format_pieces-selftests.c
+++ b/gdb/unittests/format_pieces-selftests.c
@@ -76,12 +76,56 @@
     }, true);
 }
 
+/* Test the different size modifiers that can be applied to an integer
+   argument.  Test with different integer format specifiers too.  */
+
+static void
+test_format_int_sizes ()
+{
+  check ("Hello\\t %hu%lu%llu%zu", /* ARI: %ll */
+    {
+      format_piece ("Hello\t ", literal_piece, 0),
+      format_piece ("%hu", int_arg, 0),
+      format_piece ("%lu", long_arg, 0),
+      format_piece ("%llu", long_long_arg, 0), /* ARI: %ll */
+      format_piece ("%zu", size_t_arg, 0)
+    });
+
+  check ("Hello\\t %hx%lx%llx%zx", /* ARI: %ll */
+    {
+      format_piece ("Hello\t ", literal_piece, 0),
+      format_piece ("%hx", int_arg, 0),
+      format_piece ("%lx", long_arg, 0),
+      format_piece ("%llx", long_long_arg, 0), /* ARI: %ll */
+      format_piece ("%zx", size_t_arg, 0)
+    });
+
+  check ("Hello\\t %ho%lo%llo%zo", /* ARI: %ll */
+    {
+      format_piece ("Hello\t ", literal_piece, 0),
+      format_piece ("%ho", int_arg, 0),
+      format_piece ("%lo", long_arg, 0),
+      format_piece ("%llo", long_long_arg, 0), /* ARI: %ll */
+      format_piece ("%zo", size_t_arg, 0)
+    });
+
+  check ("Hello\\t %hd%ld%lld%zd", /* ARI: %ll */
+    {
+      format_piece ("Hello\t ", literal_piece, 0),
+      format_piece ("%hd", int_arg, 0),
+      format_piece ("%ld", long_arg, 0),
+      format_piece ("%lld", long_long_arg, 0), /* ARI: %ll */
+      format_piece ("%zd", size_t_arg, 0)
+    });
+}
+
 static void
 run_tests ()
 {
   test_escape_sequences ();
   test_format_specifier ();
   test_gdb_formats ();
+  test_format_int_sizes ();
 }
 
 } /* namespace format_pieces */
