Step 0: Checkout and Compile the Kernel

In the preparation phase, we checkout and compile the repositories needed to get started with working with LITMUS^RT.

First, obtain a copy of the LITMUS^RT kernel.

$ git clone http://www.litmus-rt.org/src/litmus-rt.git
Cloning into litmus-rt...                                                                                                                                                                                       
$ cd litmus-rt/                                                                                                                                                               
$ ls
COPYING  Documentation  Kconfig      Makefile  REPORTING-BUGS  block   drivers   fs       init  kernel  litmus  net      scripts   sound  usr
CREDITS  Kbuild         MAINTAINERS  README    arch            crypto  firmware  include  ipc   lib     mm      samples  security  tools  virt

Next, obtain a working kernel configuration. For this tutorial, we are going to use the default KVM configuration.

$ wget http://www.litmus-rt.org/releases/2014.2/x86_64-config                                                                                                       
[...]
2014-06-12 15:52:49 (8.31 MB/s) - "x86_64-config" saved [65001/65001]
$ cp x86_64-config .config

Compile the kernel. On x86, the kernel build target is bzImage. Note that we do not compile modules for the default KVM configuration because all necessary drivers are statically compiled into the kernel image.

$ make -j16 bzImage
[...]
  CC      arch/x86/boot/compressed/cmdline.o
  CC      arch/x86/boot/compressed/early_serial_console.o
  OBJCOPY arch/x86/boot/compressed/vmlinux.bin
  HOSTCC  arch/x86/boot/compressed/mkpiggy
  GZIP    arch/x86/boot/compressed/vmlinux.bin.gz
  MKPIGGY arch/x86/boot/compressed/piggy.S
  AS      arch/x86/boot/compressed/piggy.o
  LD      arch/x86/boot/compressed/vmlinux
  ZOFFSET arch/x86/boot/zoffset.h
  OBJCOPY arch/x86/boot/vmlinux.bin
  AS      arch/x86/boot/header.o
  LD      arch/x86/boot/setup.elf
  OBJCOPY arch/x86/boot/setup.bin
  BUILD   arch/x86/boot/bzImage
Root device is (8, 1)
Setup is 14908 bytes (padded to 15360 bytes).
System is 3334 kB
CRC 3e3102d9
Kernel: arch/x86/boot/bzImage is ready  (#1)

(The exact numbers don't matter and will differ depending the configuration, the current version of LITMUS^RT, your compiler version, etc.)

Next, obtain a copy of liblitmus, the corresponding userspace library

$ git clone http://www.litmus-rt.org/src/liblitmus.git
Cloning into liblitmus...
$ cd liblitmus/
$ ls
INSTALL  Makefile  README  arch  bin  inc  include  setsched  showsched  src  tests

You can run make doc to get browsable documentation in docs/.

Finally, compile liblitmus. Note that this must occur after checking out the kernel since the liblitmus build system pulls some headers out of the kernel repository.

$ make
cp ../litmus-rt/include/litmus/rt_param.h include/litmus/rt_param.h
[...]
gcc -o runtests -m64  core_api.o fdso.o locks.o pcp.o runner.o   -L. -llitmus

We are now ready to start hacking LITMUS^RT.

On to the next step.