anchor.diff:  #######################################
   # Spike (ISA simulator) builder image #
   #######################################
  -FROM ubuntu:18.04 AS spikebuilder
  +FROM ubuntu:rolling AS spikebuilder
   
   # specify work directory and RISC-V install directory
   ENV TOP=/opt RISCV=/opt/riscv PATH=$PATH:/opt/riscv/bin
  
positive.code: ###################################
  # PK (Proxy kernel) builder image #
  ###################################
  FROM ubuntu:18.10 AS pkbuilder
  
  # specify work directory and RISC-V install directory
  ENV TOP=/opt RISCV=/opt/riscv PATH=$PATH:/opt/riscv/bin
  
negative.code: ########################################
  # Boolector (SMT solver) builder image #
  ########################################
  FROM ubuntu:rolling AS boolectorbuilder
  
  # specify work directory and RISC-V install directory
  ENV TOP=/opt RISCV=/opt/riscv PATH=$PATH:/opt/riscv/bin
  