Booting RISC-V Linux with qemu

There are various open source ISAs and chip designs. I’ve previously run OpenRISC 1200 on an FPGA. Another effort is the RISC-V (“RISC Five”) project, which is developing an open, patent-free 64 bit ISA. It has a sister project lowRISC which aims to produce a synthesizable RISC-V FPGA design “in 6 months”, and tape out by the end of this year (I’m a little skeptical of the timeframes).

RISC-V has added support to a fork of qemu:

$ git remote add riscv https://github.com/riscv/riscv-qemu
$ git fetch riscv
$ git checkout -b riscv-master --track riscv/master
$ ./configure --target-list="riscv-softmmu"
$ make
$ ./riscv-softmmu/qemu-system-riscv -cpu \?
RISCV 'riscv-generic'
$ ./riscv-softmmu/qemu-system-riscv -machine \?
Supported machines are:
board                RISCV Board (default)
none                 empty machine

To save yourself a world of pain, download a RISC-V Linux kernel binary and root image from here.

$ file ~/vmlinux
/home/rjones/vmlinux: ELF 64-bit LSB executable, UCB RISC-V, version 1 (SYSV), statically linked, BuildID[sha1]=d0a6d680362018e0f3b9208a7ea7f79b2b403f7c, not stripped

Then you can boot the image in the usual way:

$ ./riscv-softmmu/qemu-system-riscv \
    -display none \
    -kernel ~/vmlinux \
    -hda ~/root.bin \
    -serial stdio

The root filesystem is very sparse:

# uname -a
Linux ucbvax 3.14.15-g4073e84-dirty #4 Sun Jan 11 07:17:06 PST 2015 riscv GNU/Linux
# ls /bin
ash       chgrp     dd        ln        mv        rmdir     touch
base64    chmod     df        ls        nice      sleep     true
busybox   chown     echo      mkdir     printenv  stat      uname
cat       cp        false     mknod     pwd       stty      usleep
catv      date      fsync     mount     rm        sync
# ls /sbin
init
# ls /usr/bin
[          dirname    groups     mkfifo     sha1sum    tac        uniq
[[         dos2unix   head       nohup      sha256sum  tail       unix2dos
basename   du         hostid     od         sha3sum    tee        uudecode
cal        env        id         printf     sha512sum  test       uuencode
cksum      expand     install    readlink   sort       tr         wc
comm       expr       logname    realpath   split      tty        whoami
cut        fold       md5sum     seq        sum        unexpand   yes

Obligatory comic strip