Source：http://shantonu.blogspot.jp/2014/10/building-xnu-for-os-x-1010-yosemite.html

The OS X kernel source (xnu) has been released for OS X 10.10 Yosemite: 

Building xnu requires Xcode and some additional open-source (but not pre-installed) dependencies. You can build xnu manually by doing:

1. Install OS X Yosemite and Xcode 6.1 from the Mac App Store, make sure the Xcode license has been agreed-to with "sudo xcodebuild -license"
2. Download the source for the dtrace and AvailabilityVersions projects, which are required dependencies, as well as xnu itself

   $ curl -O http://opensource.apple.com/tarballs/dtrace/dtrace-147.tar.gz$ curl -O http://opensource.apple.com/tarballs/AvailabilityVersions/AvailabilityVersions-9.tar.gz$ curl -O http://opensource.apple.com/tarballs/xnu/xnu-2782.1.97.tar.gz

3. Build and install CTF tools from dtrace

   $ tar zxf dtrace-147.tar.gz$ cd dtrace-147$ mkdir -p obj sym dst$ xcodebuild install -target ctfconvert -target ctfdump -target ctfmerge ARCHS="x86_64" SRCROOT=$PWD OBJROOT=$PWD/obj SYMROOT=$PWD/sym DSTROOT=$PWD/dst...$ sudo ditto $PWD/dst/usr/local /usr/localPassword:$ cd ..

4. Install AvailabilityVersions

   $ tar zxf AvailabilityVersions-9.tar.gz$ cd AvailabilityVersions-9$ mkdir -p dst$ make install SRCROOT=$PWD DSTROOT=$PWD/dst$ sudo ditto $PWD/dst/usr/local `xcrun -sdk macosx -show-sdk-path`/usr/local$ cd ..

5. Build xnu

   $ tar zxf xnu-2782.1.97.tar.gz$ cd xnu-2782.1.97$ make SDKROOT=macosx ARCH_CONFIGS=X86_64 KERNEL_CONFIGS=RELEASE

See xnu's top-level README for additional build variables that can be passed on the command-line, such as BUILD_LTO=0 .

Update: If you are attempting to add system calls, you may also need to build Libsyscall.

1. Download the Libsystem source

   $ curl -O http://opensource.apple.com/tarballs/Libsystem/Libsystem-1213.tar.gz

2. Install Libsystem headers

   $ tar zxf Libsystem-1213.tar.gz $ cd Libsystem-1213$ xcodebuild installhdrs -sdk macosx ARCHS='x86_64 i386' SRCROOT=$PWD OBJROOT=$PWD/obj SYMROOT=$PWD/sym DSTROOT=$PWD/dst$ sudo ditto $PWD/dst `xcrun -sdk macosx -show-sdk-path`$ cd ..

3. Install xnu and Libsyscall headers

   $ cd xnu-2782.1.97$ mkdir -p BUILD.hdrs/obj BUILD.hdrs/sym BUILD.hdrs/dst$ make installhdrs SDKROOT=macosx ARCH_CONFIGS=X86_64 SRCROOT=$PWD OBJROOT=$PWD/BUILD.hdrs/obj SYMROOT=$PWD/BUILD.hdrs/sym DSTROOT=$PWD/BUILD.hdrs/dst$ xcodebuild installhdrs -project libsyscall/Libsyscall.xcodeproj -sdk macosx ARCHS='x86_64 i386' SRCROOT=$PWD/libsyscall OBJROOT=$PWD/BUILD.hdrs/obj SYMROOT=$PWD/BUILD.hdrs/sym DSTROOT=$PWD/BUILD.hdrs/dst$ sudo ditto BUILD.hdrs/dst `xcrun -sdk macosx -show-sdk-path`

4. Build Libsyscall

   $ mkdir -p BUILD.libsyscall/obj BUILD.libsyscall/sym BUILD.libsyscall/dst$ xcodebuild install -project libsyscall/Libsyscall.xcodeproj -sdk macosx ARCHS='x86_64 i386' SRCROOT=$PWD/libsyscall OBJROOT=$PWD/BUILD.libsyscall/obj SYMROOT=$PWD/BUILD.libsyscall/sym DSTROOT=$PWD/BUILD.libsyscall/dst