How to build XNU:

1) Type: "make"

  This builds all the components for all architectures defined in 
  ARCH_CONFIGS and for all kernel configurations defined in KERNEL_CONFIGS.
  By default, ARCH_CONFIGS contains one architecture, the build machine 
  architecture, and KERNEL_CONFIGS is set to build for RELEASE.
  This will also create a bootable image, mach_kernel,  and a kernel binary 
  with symbols, mach_kernel.sys.

  Example:
    $(OBJROOT)/RELEASE_PPC/osfmk/RELEASE/osfmk.o: pre-linked object for osfmk component
    $(OBJROOT)/RELEASE_PPC/mach_kernel: bootable image

2) Building a Component

  Go to the top directory in your XNU project.

  If you are using a sh-style shell, run the following command:
     $ . SETUP/setup.sh

  If you are using a csh-style shell, run the following command:
     % source SETUP/setup.csh

  This will define the following environmental variables:
    SRCROOT, OBJROOT, DSTROOT, SYMROOT

  From a component top directory:

    $ make all

  This builds a component for all architectures defined in ARCH_CONFIGS 
  and for all kernel configurations defined in KERNEL_CONFIGS. 
  By default, ARCH_CONFIGS contains one architecture, the build machine 
  architecture, and KERNEL_CONFIGS is set to build for RELEASE .

  Example:
    $(OBJROOT)/RELEASE_PPC/osfmk/RELEASE/osfmk.o: pre-linked object for osfmk component

  From the component top directory:

    $ make mach_kernel

  This includes your component in the bootable image, mach_kernel,  and 
  in the kernel binary with symbols, mach_kernel.sys.

  WARNING: If a component header file has been modified, you will have to do 
           the above procedure 1.

3) Building DEBUG

  Define KERNEL_CONFIGS to DEBUG in your environment or when running a 
  make command.  Then, apply procedures 4, 5

  $ make KERNEL_CONFIGS=DEBUG all

  or

  $ export KERNEL_CONFIGS=DEBUG
  $ make all

  Example:
    $(OBJROOT)/DEBUG_PPC/osfmk/DEBUG/osfmk.o: pre-linked object for osfmk component
    $(OBJROOT)/DEBUG_PPC/mach_kernel: bootable image

4) Building fat

  Define ARCH_CONFIGS in your environment or when running a make command.
  Apply procedures 3, 4, 5

  $ make ARCH_CONFIGS="PPC I386" exporthdrs all

  or

  $ export ARCH_CONFIGS="PPC I386"
  $ make exporthdrs all

5) Build check before integration

  From the top directory, run:

    $ ~rc/bin/buildit . -arch ppc -arch i386 -noinstallsrc -nosum

6) Creating tags and cscope

  Set up your build environment as per instructions in 2a

  From the top directory, run:

    $ make tags		# this will build ctags and etags

    $ make cscope	# this will build cscope database