why is va_arg returning wrong data?

Question

I am trying to port an embedded OS to a new platform and I am facing some problems with the filesystem component. I stepped in the code to finally localize the problem: The function call relevant to my case is

    // int64_t vnid = 1;
    // int32_t vid = 0;
    ...
    vnode = queue_lookup (& vnode_manager . vnode_list,
                vnode_id_inspector, vnid, vid);

And here is the queue_lookup declaration:

    void * queue_lookup (queue_t * queue, queue_inspector_t inspector, ...)
    {
      bool result;
      va_list list, list_copy;
      queue_link_t * item = NULL;

      va_start (list, inspector);

      if (queue -> status != 0)
      {
        for (item = queue -> head; item != NULL; item = item -> next)
        {
          result = false;

          va_copy (list_copy, list);
          result = inspector (item, list_copy);
          va_end (list_copy);

          if (result) break;
        }
      }

      va_end (list);
      return item;
    }

and finally, here is the vnode_id_inspector declaration:

    bool vnode_id_inspector (void * node, va_list list)
    {
      vnode_t vnode = node;
      int64_t vnid = va_arg (list, int64_t);
      int32_t vid = va_arg (list, int32_t);

      watch (bool)
      {
        ensure (vnode != NULL, false);
        return vnode -> id == vnid && vnode -> volume -> id == vid;
      }
    }

Now the problem is when I call queue_lookup with vnid=1 and vid=0, I get vnid=1 and vid=1145248 in the vnode_id_inspector !

How can I fix this issue with as minimum code change as possible ?

Regards,

Edit: add some debug info

    (gdb) p vnode_manager . vnode_list
    $44 = {lock = 1, head = 0x167770, tail = 0x167770, status = 1}
    (gdb) p vnode_manager . vnode_list ->head
    $45 = (queue_link_t *) 0x167770
    (gdb) p *(vnode_t)vnode_manager . vnode_list ->head
    $46 = {link = {next = 0x0}, id = 1, volume = 0x166370, destroy = false, 
      usage_counter = 1, data = 0x166430}
    (gdb) p *(volume_t)((vnode_t)vnode_manager . vnode_list ->head)->volume
    $47 = {link = {next = 0x0}, id = 0, root_vnid = 1, lock = 0, host_volume = 0x0, 
      host_vnid = -1, cmd = 0x13a768 <rootfs_cmd>, data = 0x1663d0}

Answer 1

I solved this issue, there was a problem in the stack alignment. I fixed it by making some adjustment in the cpu_context_switch.s to align the stack to 8bytes instead of 4bytes .