Bug 20137 - Fix alignment usage when demarshaling basics

We can't safely type-pun from e.g. char * to DBusBasicValue *, because
the latter has higher alignment requirements.  Instead, create an
explicit pointer for each case.

Also, we mark each one volatile to sidestep strict aliasing issues, for
the future when we turn on strict aliasing support.

Original patch and review from Jay Estabrook <jay.estabrook@hp.com>.

diff --git a/dbus/dbus-marshal-basic.c b/dbus/dbus-marshal-basic.c
index 724d94b..38fbe2d 100644 (file)
--- a/dbus/dbus-marshal-basic.c
+++ b/dbus/dbus-marshal-basic.c
@@ -508,59 +508,74 @@ _dbus_marshal_read_basic (const DBusString      *str,
                           int                   *new_pos)
 {
   const char *str_data;
-  DBusBasicValue *vp;
 
   _dbus_assert (dbus_type_is_basic (type));
 
   str_data = _dbus_string_get_const_data (str);
-  vp = value;
 
+  /* Below we volatile types to avoid aliasing issues;
+   * see http://bugs.freedesktop.org/show_bug.cgi?id=20137
+   */
+  
   switch (type)
     {
     case DBUS_TYPE_BYTE:
-      vp->byt = _dbus_string_get_byte (str, pos);
+      {
+      volatile unsigned char *vp = value;
+      *vp = (unsigned char) _dbus_string_get_byte (str, pos);
       (pos)++;
+      }
       break;
     case DBUS_TYPE_INT16:
     case DBUS_TYPE_UINT16:
+      {
+      volatile dbus_uint16_t *vp = value;
       pos = _DBUS_ALIGN_VALUE (pos, 2);
-      vp->u16 = *(dbus_uint16_t *)(str_data + pos);
+      *vp = *(dbus_uint16_t *)(str_data + pos);
       if (byte_order != DBUS_COMPILER_BYTE_ORDER)
-       vp->u16 = DBUS_UINT16_SWAP_LE_BE (vp->u16);
+       *vp = DBUS_UINT16_SWAP_LE_BE (*vp);
       pos += 2;
+      }
       break;
     case DBUS_TYPE_INT32:
     case DBUS_TYPE_UINT32:
     case DBUS_TYPE_BOOLEAN:
+      {
+      volatile dbus_uint32_t *vp = value;
       pos = _DBUS_ALIGN_VALUE (pos, 4);
-      vp->u32 = *(dbus_uint32_t *)(str_data + pos);
+      *vp = *(dbus_uint32_t *)(str_data + pos);
       if (byte_order != DBUS_COMPILER_BYTE_ORDER)
-       vp->u32 = DBUS_UINT32_SWAP_LE_BE (vp->u32);
+       *vp = DBUS_UINT32_SWAP_LE_BE (*vp);
       pos += 4;
+      }
       break;
     case DBUS_TYPE_INT64:
     case DBUS_TYPE_UINT64:
     case DBUS_TYPE_DOUBLE:
+      {
+      volatile dbus_uint64_t *vp = value;
       pos = _DBUS_ALIGN_VALUE (pos, 8);
 #ifdef DBUS_HAVE_INT64
       if (byte_order != DBUS_COMPILER_BYTE_ORDER)
-        vp->u64 = DBUS_UINT64_SWAP_LE_BE (*(dbus_uint64_t*)(str_data + pos));
+        *vp = DBUS_UINT64_SWAP_LE_BE (*(dbus_uint64_t*)(str_data + pos));
       else
-        vp->u64 = *(dbus_uint64_t*)(str_data + pos);
+        *vp = *(dbus_uint64_t*)(str_data + pos);
 #else
-      vp->u64 = *(DBus8ByteStruct*) (str_data + pos);
+      *vp = *(DBus8ByteStruct*) (str_data + pos);
       swap_8_octets (vp, byte_order);
 #endif
       pos += 8;
+      }
       break;
     case DBUS_TYPE_STRING:
     case DBUS_TYPE_OBJECT_PATH:
       {
         int len;
+        volatile char **vp = value;
 
         len = _dbus_marshal_read_uint32 (str, pos, byte_order, &pos);
 
-        vp->str = (char*) str_data + pos;
+        *vp = (char*) str_data + pos;
 
         pos += len + 1; /* length plus nul */
       }
@@ -568,11 +583,12 @@ _dbus_marshal_read_basic (const DBusString      *str,
     case DBUS_TYPE_SIGNATURE:
       {
         int len;
+        volatile char **vp = value;
 
         len = _dbus_string_get_byte (str, pos);
         pos += 1;
 
-        vp->str = (char*) str_data + pos;
+        *vp = (char*) str_data + pos;
 
         pos += len + 1; /* length plus nul */
       }