Re: [hurd-amd64] ibus test failures

[Diego Nieto Cid]

On Tue, Dec 31, 2024 at 08:32:47PM +0000, Diego Nieto Cid wrote:
> 
> Adding the following line to the program:
> 
>     printf("cmsghdr: %lu\n", sizeof (struct cmsghdr));
> 
> shows 12 on Hurd and 16 on Linux. I think I'm closer :)

The only difference in the structure definition is the cmsg_len field type
which happens to be the 4 missing bytes.

--- >8 --- >8 ---
Linux
=====

    /* Structure used for storage of ancillary data object information.  */
    struct cmsghdr
     {
        size_t cmsg_len;            /* Length of data in cmsg_data plus length
                                       of cmsghdr structure.
                                       !! The type should be socklen_t but the
                                       definition of the kernel is incompatible
                                       with this.  */
        int cmsg_level;             /* Originating protocol.  */
        int cmsg_type;              /* Protocol specific type.  */
    #if __glibc_c99_flexarr_available
        __extension__ unsigned char __cmsg_data __flexarr; /* Ancillary data.  
*/
    #endif
      };

Hurd
====

    /* 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.  */
        int cmsg_level;             /* Originating protocol.  */
        int cmsg_type;              /* Protocol specific type.  */
    #if __glibc_c99_flexarr_available
        __extension__ unsigned char __cmsg_data __flexarr; /* Ancillary data.  
*/
    #endif
  };
--- >8 --- >8 ---

So, while CMSG_LEN aligns the cmsghdr structure, CMSG_DATA don't. I think 
that's the problem.