In iconvconfig.h, there are

typedef uint16_t gidx_t;


struct gconvcache_header
{
  uint32_t magic;
  gidx_t string_offset;
  gidx_t hash_offset;
  gidx_t hash_size;
  gidx_t module_offset;
  gidx_t otherconv_offset;
};

But in iconvconfig.c, there are

/* Format of the output file.

   Offset   Length       Description
   0000     4            Magic header bytes
   0004     4            Offset of string table (stoff)
   0008     4            Offset of name hashing table (hoff)
   000C     4            Hashing table size (hsize)
   0010     4            Offset of module table (moff)
   0014     4            Offset of other conversion module table (ooff)

   stoff    ???          String table

The lengths of stoff, hoff, hsize, moff and ooff are 2 not 4.

Also compiler may put padding in struct gconvcache_header, which may not
be initialized. When write_output does

  iov[0].iov_base = &header;
  iov[0].iov_len = sizeof (struct gconvcache_header);
  total = iov[0].iov_len;

we may get different values in padding for different compilers.