commit 520dcf39f7b78a3b1db93c9be6a1c120eda699cd
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Feb 12 17:04:34 2016 +0100

    bits/socket.h: Define struct sockaddr with may_alias attribute [BZ #19622]
    
    As suggested by Marek Polacek.
    
    Using struct sockaddr with aliasing violations is quite common, and the
    POSIX interfaces more or less encourage it.

diff --git a/bits/socket.h b/bits/socket.h
index ab9f242..666842b 100644
--- a/bits/socket.h
+++ b/bits/socket.h
@@ -144,7 +144,7 @@ enum __socket_type
 #include <bits/sockaddr.h>
 
 /* Structure describing a generic socket address.  */
-struct sockaddr
+struct __attribute_may_alias__ sockaddr
   {
     __SOCKADDR_COMMON (sa_);	/* Common data: address family and length.  */
     char sa_data[14];		/* Address data.  */
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 7fd4154..aee6ae3 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -407,6 +407,12 @@
       [!!sizeof (struct { int __error_if_negative: (expr) ? 2 : -1; })]
 #endif
 
+#if __GNUC_PREREQ (4,0)
+# define __attribute_may_alias__ __attribute__ ((__may_alias__))
+#else
+# define __attribute_may_alias__
+#endif
+
 #include <bits/wordsize.h>
 
 #if defined __LONG_DOUBLE_MATH_OPTIONAL && defined __NO_LONG_DOUBLE_MATH
diff --git a/sysdeps/mach/hurd/bits/socket.h b/sysdeps/mach/hurd/bits/socket.h
index 02c5dac..bc26a28 100644
--- a/sysdeps/mach/hurd/bits/socket.h
+++ b/sysdeps/mach/hurd/bits/socket.h
@@ -148,7 +148,7 @@ enum __socket_type
 #include <bits/sockaddr.h>
 
 /* Structure describing a generic socket address.  */
-struct sockaddr
+struct __attribute_may_alias__ sockaddr
   {
     __SOCKADDR_COMMON (sa_);	/* Common data: address family and length.  */
     char sa_data[14];		/* Address data.  */
diff --git a/sysdeps/unix/sysv/linux/bits/socket.h b/sysdeps/unix/sysv/linux/bits/socket.h
index 0581c79..a1fc921 100644
--- a/sysdeps/unix/sysv/linux/bits/socket.h
+++ b/sysdeps/unix/sysv/linux/bits/socket.h
@@ -150,7 +150,7 @@ typedef __socklen_t socklen_t;
 #include <bits/sockaddr.h>
 
 /* Structure describing a generic socket address.  */
-struct sockaddr
+struct __attribute_may_alias__ sockaddr
   {
     __SOCKADDR_COMMON (sa_);	/* Common data: address family and length.  */
     char sa_data[14];		/* Address data.  */