Make sure you followed the install instructions to prepare the system and install the compiler toolchain.
$ cd $REPO_TOP/sw/hello_world $ make CC=/tools/riscv/bin/riscv32-unknown-elf-gcc
The build process produces a variety of output files.
.elf: the linked program in ELF format.bin: the linked program as plain binary.dis: the disassembled program.vmem: a Verilog memory file which can be read by $readmemh() in Verilog code