Re: [hurd-amd64] ibus test failures

[Diego Nieto Cid]

On Wed, Jan 01, 2025 at 06:51:47PM +0100, Samuel Thibault wrote:
> > 
> >     /* Structure used for storage of ancillary data object information.  */
> >     struct cmsghdr
> >       {
> >         socklen_t cmsg_len;         /* Length of data in cmsg_data plus 
> > length
> >                                        of cmsghdr structure.  */
> 
> That's the correct type according to posix:
> 
> ./basedefs/sys_socket.h.html:<tt>socklen_t  cmsg_len   </tt> Data byte count, 
> including the <b>cmsghdr</b>. <tt>
>

Ok, but we are giving unaligned data pointers with the current implementation
of CMSG_DATA.

GLib has the following code to parse control messages

    control_message = g_socket_control_message_deserialize (cmsg->cmsg_level,
                    cmsg->cmsg_type,
                    cmsg->cmsg_len - ((char *)CMSG_DATA (cmsg) - (char *)cmsg),

the third parameter is the size of the ancillary data. And CMSG_DATA should
align the header structure size for it to work (bacause cmsg_len was computed
with CMSG_LEN which aligns the header).

Something like the definition below could work, (except for when felxarr are
available):

    #define CMSG_DATA(cmsg) ((unsigned char *) (cmsg) + (CMSG_ALIGN (sizeof 
(struct cmsghdr))))