xtensa: reading privileged special registers

[Max Filippov <jcmvbkbc@gmail.com>]

Hello.

I'm trying to read privileged SRs from a remote gdbserver by the gdb configured for the elf target. All gdb versions that I've tried (6.8, 7.2 and 7.3) return 0 for those registers.
Running gdb under gdb showed that reading those registers ends inside xtensa_pseudo_register_read in the following block:

[...]
  /* We have to find out how to deal with priveleged registers.
     Let's treat them as pseudo-registers, but we cannot read/write them.  */

  else if (regnum < gdbarch_tdep (gdbarch)->a0_base)
    {
      buffer[0] = (gdb_byte)0;
      buffer[1] = (gdb_byte)0;
      buffer[2] = (gdb_byte)0;
      buffer[3] = (gdb_byte)0;
    }
[...]

The question is is there any reason we cannot read/write them with the elf target?
What would be the right way to make privileged SRs available to gdb?

Thanks.
-- Max