VSM data are aligned to 32/64 bit boundary

Till now the VSM buffer was aligned to 16 bit boundary
which could possibly cause problems on RISC architectures
when accessing the message data in unsafe manner.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/config.hpp

@@ -39,10 +39,6 @@ namespace zmq
         //  Commands in pipe per allocation event.
         command_pipe_granularity = 16,
 
-        //  Size in bytes of the largest message that is still copied around
-        //  rather than being reference-counted.
-        max_vsm_size = 29,
-
         //  Determines how often does socket poll for new commands when it
         //  still has unprocessed messages to handle. Thus, if it is set to 100,
         //  socket will process 100 inbound messages before doing the poll.

src/msg.cpp

@@ -19,6 +19,7 @@
 */
 
 #include "msg.hpp"
+#include "../include/zmq.h"
 
 #include <string.h>
 #include <errno.h>
@@ -29,6 +30,11 @@
 #include "likely.hpp"
 #include "err.hpp"
 
+//  Check whether the sizes of public representation of the message (zmq_msg_t)
+//  and private represenation of the message (zmq::msg_t) match.
+typedef char zmq_msg_size_check
+    [2 * ((sizeof (zmq::msg_t) == sizeof (zmq_msg_t)) != 0) - 1];
+
 bool zmq::msg_t::check ()
 {
      return u.base.type >= type_min && u.base.type <= type_max;

src/msg.hpp

@@ -77,6 +77,10 @@ namespace zmq
 
     private:
 
+        //  Size in bytes of the largest message that is still copied around
+        //  rather than being reference-counted.
+        enum {max_vsm_size = 29};
+
         //  Shared message buffer. Message data are either allocated in one
         //  continuous block along with this structure - thus avoiding one
         //  malloc/free pair or they are stored in used-supplied memory.
@@ -109,21 +113,24 @@ namespace zmq
         //  the union.
         union {
             struct {
+                unsigned char unused [max_vsm_size + 1];
                 unsigned char type;
                 unsigned char flags;
             } base;
             struct {
+                unsigned char data [max_vsm_size];
+                unsigned char size;
                 unsigned char type;
                 unsigned char flags;
-                unsigned char size;
-                unsigned char data [max_vsm_size];
             } vsm;
             struct {
+                content_t *content;
+                unsigned char unused [max_vsm_size + 1 - sizeof (content_t*)];
                 unsigned char type;
                 unsigned char flags;
-                content_t *content;
             } lmsg;
             struct {
+                unsigned char unused [max_vsm_size + 1];
                 unsigned char type;
                 unsigned char flags;
             } delimiter;