On Wed, Jan 01, 2025 at 08:07:04PM +0000, Diego Nieto Cid wrote:
> 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.
>
On the other hand, nothing says the pointer shall be aligned:
CMSG_DATA(cmsg) [1]
If the argument is a pointer to a cmsghdr structure, this macro
shall return an unsigned character pointer to the data array
associated with the cmsghdr structure.
[1] https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_socket.h.html
and GLib computation is relying on undefined behaviour.
