Build Xinu

The new MIPS port of Embedded XINU has been released. See the Downloads tab for more information. A revision of Doug Comer's venerable Operating System Design - The XINU Approach textbook is in progress.

Cross-Compiler

In order to compile Embedded MIPS kernels on a workstation that is not itself a MIPS processor, it is necessary to build and install an appropriate cross compiler. There are many ways to accomplish this; for reference, we list the specific versions and steps we used for our installation.

As always, one should be wary of installing unfamilar software as the root user of the system. All of the steps below have been carried out as a lesser-privileged user with write access to the necessary directories.

First, we downloaded, compiled, and installed the appropriate binary utilities. We downloaded binutils version 2.18, untarred the source code, and ran the following commands inside the new directory created by untarring the download:

  ./configure  --prefix=/usr/local/project/mipsel-dev --target=mipsel
  make
  make install

We have chosen the path "/usr/local/project/mipsel-dev" to host our cross-compiler installation. Whatever path is used here must be reflected in the XINU build configuration file, "compile/makeVars" when you arrive at that step.

We are not building a true, full-blown UNIX cross-compiler here, and do not need a proper installation of the platform-specific C libraries; XINU has its own small libraries that compile with the kernel. However, the GCC compilation will want to see appropriate library headers, so we cheat here by linking the platform-specific include directory to the host machine's include directory.

  mkdir -p /usr/local/project/mipsel-dev/mipsel/usr
  ln -s /usr/include /usr/local/project/mipsel-dev/mipsel/usr/include

Second, we downloaded, patched, compiled and installed the GNU C Compiler. We downloaded GCC version 3.4.6. We applied a short patch to correct some kind of obscure fixproto error. We added the newly compiled binutils into the shell path (/usr/local/project/mipsel-dev/bin) for the gcc compilation to find them. This is also known to work with GCC version 4.1.2 and 4.2.0 unpatched, using this script to get around installing a bunch of platform-specific UNIX libraries.

  ./configure  --prefix=/usr/local/project/mipsel-dev --target=mipsel --with-sysroot=/usr/local/project/mipsel-dev/mipsel/ --enable-languages=c
  make
  make install

If all has gone well, you should now have a gcc cross-compiler from your host's native architecture to little-endian MIPS:

  /usr/local/project/mipsel-dev/bin/mipsel-gcc

Remember the path to this file because later you'll need to double check some building variables to make sure they point to the correct location of your cross-compiler.

Building the XINU image

Once you have downloaded and extracted the xinu tarball, you will see a basic directory structure:

AUTHORS   include/  LICENSE   README  system/  tty/
compile/  lib/      loader/   shell/  test/    uart/

AUTHORS is a brief history of contributors to the XINU operating system in it's varying iterations.

compile/ contains the Makefile and other necesities for building the XINU system once you have a cross-compiler.

include/ contains all the header files used by XINU.

lib/ contains a folder (libxc/) with a Makefile and source for the library, as well as a binary blob which contains the pre-compiled library.

LICENSE is the license under which this project falls.

loader/ contains assembly files and is where the bootloader will begin execution of O/S code.

README is this document.

shell/ contains the source for all shell related functions.

system/ contains the source for all system functions such as the nulluser process (initialize.c) as well as code to set up a C environment (startup.S).

test/ contains a number of testcases (which can be run using the shell command testsuite).

tty/ contains the source for the tty driver.

uart/ contains the source for the uart driver.

---

First, it is a good idea to read up on building the XINU system. Next, you'll want to check your mipsVars file in the compile directory. The file should look something like this:

MIPS_ROOT = /usr/local/project/mipsel-dev/bin
MIPS_PREFIX = mipsel-

COMPILER_ROOT = ${MIPS_ROOT}/${MIPS_PREFIX}

CC       = ${COMPILER_ROOT}gcc
CPP      = ${COMPILER_ROOT}cpp
LD       = ${COMPILER_ROOT}ld
AS       = ${COMPILER_ROOT}as
AR       = ${COMPILER_ROOT}ar
MAKEDEP  = `which makedepend`

DOCGEN   = doxygen

# DETAIL   = -DDETAIL

DEFS     =
INCLUDE  = -I../include

#flag for producing GDB debug information
BUGFLAG = -ggdb

CFLAGS = -O0 -Wall -Werror -Wstrict-prototypes -Wno-trigraphs            \
             -nostdinc -fno-builtin -fno-strict-aliasing -fno-common \
         -fomit-frame-pointer -fno-pic -ffunction-sections -G 0  \
         -mlong-calls -mno-abicalls -mabi=32 -march=mips32       \
         -Wa,-32 -Wa,-march=mips32 -Wa,-mips32 -Wa,--trap        \
         ${DEBUG} ${INCLUDE} ${DETAIL} ${DEFS} -c


ASFLAGS  = ${INCLUDE} ${DEBUG} -march=mips32 -mips32

The important thing to note on this file is the MIPS_ROOT variable. It needs to point to the directory containing the cross-compiler. If you followed the commands in the tutorial exactly, then the value of the MIPS_ROOT variable in the code above should be the correct value.

What to do next?

Now that you have successfully built a XINU boot image you're ready to use that file to actually boot XINU on your backend router.