Getting an ERROR: Unrecognized core:

[cghalibkhan]

Hi

 Am working in RISCV Arch (Hifive Unleashed Board), i have useen this repo to build  a gdbserver, it build successfully but not able to Run on Target Machine.
  If i Run 
 $ ./riscv32-gdbserver --core rv32gc 12345 

Error:-
ERROR: Unrecognized core: rv32gc: exiting

Can you pealse help to run on my Target Machine RISCV Hifive unleash Board.

Thank's & Regards
Ghalib khan C