GNU AS for ARM help

[Scott, Gary]

Hi
  Im am trying to get the GNU AS to work on ARM Cortex-A53 asembler files
Note these work with armasm tool but fail with GNU ASM due to System register access
The code is
MRS x0, ELR_EL1
As an example

The errors is
Error: unknown or missing system register name at operand 2 -- `mrs x0, ELR_EL1'

Can u help - Is there a missing include file I need for System Registers that maybe map
ELR_ELI to an actual internal address mechanism

Thanks

Gary