RISC-V Developer Environment

This archive includes a 6.6-rc7 kernel and Gentoo Linux userspace configured for RISC-V to enable development and testing of RVV optimizations to OSS projects.

Getting Started

This setup has been tested with qemu-8.1.2. To boot the VM simply run:

$ ./start.sh

There are two accounts available on the system, root and negge. Both have the same password: rise

At boot, the VM starts sshd on port 22. The start.sh script includes a setting to map host port 10000 to VM port 22. You can ssh in with the user account:

$ ssh -p 10000 negge@localhost

Installed Software

This machine has the latest developer tools installed. The full list of installed programs built for RISC-V can be found in packages.txt.

Testing RISC-V Extensions

There are two programs in the negge user directory:

$ ls test
hwcap  hwcap.c  testrvv  testrvv.as  testrvv.o

1. The hwcap program tests that the 'V' bit is set by getauxval(AT_HWCAP)
2. The testrvv program executes the vsetvli instruction and returns

These can be used to confirm that the 6.6-rc7 kernel is properly built with CONFIG_RISCV_ISA_V=y and CONFIG_RISCV_ISA_V_DEFAULT_ENABLE=y.

Advanced Use

It is possible to use qemu-binfmt to mount and run the system in a chroot. This has the advantage of using the host kernel and MMU and is significantly faster. If you have not set up binfmt_misc before, see the section Setting up binfmt_misc.

As root, configure and start the qemu-binfmt service. You can confirm this is done correctly with:

$ cat /proc/sys/fs/binfmt_misc/qemu-riscv64
enabled
interpreter /usr/bin/qemu-riscv64
...

The VM already contains a staticly compiled x86_64 QEMU 8.1.2 user binary at:

/usr/bin/qemu-riscv64

To create the chroot, run the following commands as root:

mount -o loop,offset=1048576 gentoo.img /mnt/gentoo
cp /etc/resolv.conf /mnt/gentoo/etc
mount --bind /proc /mnt/gentoo/proc
mount --bind /sys /mnt/gentoo/sys
mount --bind /dev /mnt/gentoo/dev
mount --bind /dev/pts /mnt/gentoo/dev/pts
mount --bind /dev/shm /mnt/gentoo/dev/shm

You can enter the chroot with:

chroot /mnt/gentoo /bin/bash
env-update && source /etc/profile

Using the chroot is recommend for building and installing new packages into the VM with the emerge command.

Note, there are some differences between a qemu-user chroot and qemu-system

1. The host kernel is still x86_64 so /proc/cpuinfo will not show the RISC-V ISA extensions
2. Process concurrency is handled by the host kernel

For this reason it is recommended to develop and test RVV optimizations in the emulated VM.

Setting up binfmt_misc

The way in which binfmt_misc is set up depends on the system that is used, but requires root access in all cases.

At the end of this, the binfmt_misc entry for qemu-riscv64 will point to the path that is expected in the chroot. The entry will also point to a standard installation path for the QEMU binaries.

Ubuntu

It is assumed that the QEMU interpreter required is the one installed from the package manager.

sudo apt install qemu-user-static

The path to the interpreter stored in binfmt_misc then points to a symlink, where we want to point to the actual interpreter.

sudo apt install binfmt-support
sudo sed -i 's|interpreter .*|interpreter /usr/bin/qemu-riscv64-static|' /usr/share/binfmts/qemu-riscv64
sudo update-binfmts --importdir /usr/share/binfmts --import qemu-riscv64
cat /proc/sys/fs/binfmt_misc/qemu-riscv64
# enabled
# interpreter /usr/bin/qemu-riscv64-static
# ...

You should now be able to follow the remaining instructions from the previous section to launch the chroot.