Tutorial:Booting XNU on A4 Devices
Hello, I am 3x7R00Tripper and in this post I will present how can you boot xnu on all apple a4 devices. I do it with my iPhone 4 iOS 6.1.3
You find this post on my website also: 
First you must install CTF tools etc.
I present it with Mavericks and Mountain Lion.
$ curl -O http://opensource.apple.com/tarballs/dtrace/dtrace-118.tar.gz $ curl -O http://opensource.apple.com/tarballs/AvailabilityVersions/AvailabilityVersions-6.tar.gz $ git clone https://github.com/3x7R00Tripper/xnu $ tar zxf dtrace-118.tar.gz $ cd dtrace-118 $ 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/local $ cd .. $ tar zxf AvailabilityVersions-6.tar.gz $ cd AvailabilityVersions-6 $ mkdir -p dst $ make install SRCROOT=$PWD DSTROOT=$PWD/dst $ sudo ditto $PWD/dst/usr/local `xcrun -sdk / -show-sdk-path`/usr/local $ cd .. $ cd xnu
For Mountain Lion read this post.
Now you are in the xnu folder Know you must make it for Apple A4:
$ make TARGET_CONFIGS="debug arm S5L8930X"
After the process navigate to BUILD/obj/DEBUG_ARM_S5L8930X In this folder are many files. mach_kernel is the bootable image.
For booting the kernel you need redsn0w. Open terminal and navigate to the redsn0w folder. Now you write this commands:
$ cd redsn0w.app/Contents/MacOS $ ./redsn0w -i <'4.1 iPSW'> -k <'mach_kernel'>
Here a example command:
$ ./redsn0w -i /Users/Louis/Desktop/iOS\:Mac\ hack/XNU_Kernel_Panic_Apple_A4-Booting/iPhone3\,1_4.1_8B117_Restore.ipsw -k /Users/Louis/Desktop/xnu/BUILD/obj/DEBUG_ARM_S5L8930X/mach_kernel
-graphics-mode Enables graphics mode. Boots with an apple logo and a white spinner, kernel panics show the panic dialog
Now you must get your iDevice(A4) in the DFU mode. Wait a few seconds and a white screen will flashes on your iDevice. Now you see the pineapple on your iDevice. 30 secounds - 1 minute later the kernel is booted on your iDevice. A long time you see 'Still waiting for root device'. But If you wait more than 10 - 30 minutes, appears a kernel panic. Ok you are finished and have fun :)