Make padding in struct sockaddr_storage explicit [BZ #20111]

This avoids aliasing issues with GCC 6 in -fno-strict-aliasing
mode.  (With implicit padding, not all data is copied.)

This change makes it explicit that struct sockaddr_storage is
only 126 bytes large on m68k (unlike elsewhere, where we end up
with the requested 128 bytes).  The new test case makes sure that
this does not happen on other architectures.

2 files changed, 46 insertions, 4 deletions

diff --git a/sysdeps/unix/sysv/linux/bits/socket.h b/sysdeps/unix/sysv/linux/bits/socket.h
index a57048c04d..2eb95f7e20 100644
--- a/sysdeps/unix/sysv/linux/bits/socket.h
+++ b/sysdeps/unix/sysv/linux/bits/socket.h
@@ -175,16 +175,16 @@ struct sockaddr
 
 
 /* Structure large enough to hold any socket address (with the historical
-   exception of AF_UNIX).  We reserve 128 bytes.  */
+   exception of AF_UNIX).  */
 #define __ss_aligntype	unsigned long int
-#define _SS_SIZE	128
-#define _SS_PADSIZE	(_SS_SIZE - (2 * sizeof (__ss_aligntype)))
+#define _SS_PADSIZE \
+  (_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
 
 struct sockaddr_storage
   {
     __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
-    __ss_aligntype __ss_align;	/* Force desired alignment.  */
     char __ss_padding[_SS_PADSIZE];
+    __ss_aligntype __ss_align;	/* Force desired alignment.  */
   };
 
 
diff --git a/sysdeps/unix/sysv/linux/m68k/bits/sockaddr.h b/sysdeps/unix/sysv/linux/m68k/bits/sockaddr.h
new file mode 100644
index 0000000000..5721f99fd9
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/m68k/bits/sockaddr.h
@@ -0,0 +1,42 @@
+/* Definition of struct sockaddr_* members and sizes, Linux/m68k version.
+   Copyright (C) 1995-2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/*
+ * Never include this file directly; use <sys/socket.h> instead.
+ */
+
+#ifndef _BITS_SOCKADDR_H
+#define _BITS_SOCKADDR_H	1
+
+
+/* POSIX.1g specifies this type name for the `sa_family' member.  */
+typedef unsigned short int sa_family_t;
+
+/* This macro is used to declare the initial common members
+   of the data types used for socket addresses, `struct sockaddr',
+   `struct sockaddr_in', `struct sockaddr_un', etc.  */
+
+#define	__SOCKADDR_COMMON(sa_prefix) \
+  sa_family_t sa_prefix##family
+
+#define __SOCKADDR_COMMON_SIZE	(sizeof (unsigned short int))
+
+/* Size of struct sockaddr_storage.  */
+#define _SS_SIZE 126
+
+#endif	/* bits/sockaddr.h */