Unikernel Linux (UKL)

Unikernel Linux (UKL) is a small patch to Linux and glibc which allows you to build many programs, unmodified, as unikernels. That means they are linked with the Linux kernel into a final vmlinuz and run in kernel space. You can boot these kernels on baremetal or inside a virtual machine. Almost all features and drivers in Linux are available for use by the unikernel.

Requirements

• autoconf & automake
• GCC or Clang
• GNU make
• GNU sed
• Docker
• All the prerequisites for building the 6.3 Linux Kernel on your distro
• qemu, if you want to test boot in a virtual machine

Building the included programs

git clone https://github.com/unikernelLinux/ukl
cd ukl
git submodule update --init
autoreconf -i
./configure --with-program=hello
make -j`nproc`

To test it (requires qemu):

make boot

If the program requires incoming network connections, use this target instead. Note this runs qemu with sudo:

make boot-priv

hello is a simple hello world example. You can try one of the other programs (see subdirectories in the source) by adjusting ./configure --with-program=...

Currently you must make clean -C linux if you change the program. (This is a bug which we should fix.)

Configuration options

Some additional options are available to turn on and off features of UKL:

$ ./configure --help
...
  --enable-bypass         enable glibc bypass (UKL_BP) [default=no]
  --enable-same-stack     enable same stack (CONFIG_UKL_SAME_STACK)
                          [default=no]
  --enable-use-ret        use ret instead of iret (CONFIG_UKL_USE_RET)
                          [default=no]
  --enable-use-ist-pf     use IST for PF instead of DF (CONFIG_UKL_USE_IST_PF)
                          [default=no]
  --enable-afterspace     enable afterspace (CONFIG_UKL_CREATE_AFTERSPACE)
                          [default=no]

Building into a separate build directory

If you want to build different configurations of UKL from the same source tree, you can do this by creating separate build directories, eg:

mkdir build-hello
pushd build-hello
../configure --with-program=hello
make -j`nproc`
popd

mkdir build-redis
pushd build-redis
../configure --with-program=redis
make -j`nproc`
popd

Building your own program

We would strongly recommend looking at the example hello world program in the hello/ subdirectory.

1. You need to build it (not link) with two flags: -mno-red-zone -mcmodel=kernel
2. Then you need to do a partial link with the required libraries, glibc, libgcc etc.
3. Your partially linked application binary should be named UKL.a and needs to be copied to the top build directory for the final kernel link stage.