Friday, December 11, 2015

Building xnu for OS X 10.11 El Capitan

The OS X kernel source (xnu) has been released for OS X 10.11 El Capitan: here

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 El Capitan and Xcode 7.0, 7.1, or 7.2 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
    $ curl -O
    $ curl -O
  3. Build and install CTF tools from dtrace
    $ tar zxf dtrace-168.tar.gz
    $ cd dtrace-168
    $ 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/Applications/ /Applications/
    $ cd ..
  4. Install AvailabilityVersions
    $ tar zxf AvailabilityVersions-20.tar.gz 
    $ cd AvailabilityVersions-20
    $ 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-3247.1.106.tar.gz
    $ cd xnu-3247.1.106
See xnu's top-level README for additional build variables that can be passed on the command-line, such as BUILD_LTO=0 or KERNEL_CONFIGS=DEVELOPMENT .

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

  1. Download the Libsystem source
    $ curl -O
  2. Install Libsystem headers
    $ tar zxf Libsystem-1225.1.1.tar.gz
    $ cd Libsystem-1225.1.1
    $ 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-3247.1.106
    $ 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
    $ sudo 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
    $ sudo 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
  5. To install custom OS components, System Integrity Protection must be disabled.
  6. To install the resulting new binaries, execute:
    1. xnu:
      $ sudo cp BUILD/obj/RELEASE_X86_64/kernel /System/Library/Kernels/
      $ sudo kextcache -invalidate /
      / locked; waiting for lock.
      Lock acquired; proceeding.
      $ sudo reboot
    2. Libsyscall:
      $ sudo cp BUILD.libsyscall/dst/usr/lib/system/libsystem_kernel.dylib /usr/lib/system/
      $ sudo update_dyld_shared_cache
      $ sudo reboot