export RISCV_PATH=/opt/riscv64-unknown-elf-gcc-8.2.0-2019.05.3-x86_64-linux-ubuntu14/
make BSP=metal PROGRAM=first TARGET=sifive-hifive1-revb debug
# run
# riscv-sifive-elf-gdb software/first/debug/first.elf
# then: target remote localhost:3333 to connect to GDB debugger