Just to clear things up - I'm definitely not responsible for anything. This patch will not work on devices with locked bootloaders.
This patch was made by Mike Kasick for Samsung Epic 4G. Since that, it was ported to several devices, one of them is Asus Transformer TF201 - I used patch from TF201 and modified it a bit (basically just changed few SoC specific constants). People at #ubuntu-arm helped me out with that, thanks.
For flo, I've improved the patch a bit - only the host needs to be patched now and I also fixed a bug with /proc/atags not reading all tags.
Special thanks to Tasssadar for his kexec-hardboot patch for the Nexus 4. Also thanks to alvinhochun and krabappel2548. I borrowed some of their code.
It is syscall of Linux kernel, which allows you to boot another Linux kernel without restarting the device - "Linux boots itself". The functionality is equivalent to fastboot -c *cmdline* boot zImage initrd.img, but without PC and fastboot. It is fairly known thing, so more info at wikipedia and man kexec.
Standard kexec call unfortunatelly does not work on Nexus 4. It freezes somewhere, and it is very difficult to find out where - probably some of the drivers are not shut down/re-initialized properly, it is a commong thing among Android devices, which is why kexec-hardboot was made.
What is the difference between normal and hardboot kexec?
Kexec-hardboot patch adds a real device restart to that process, so that all the drivers can be properly reinitialized. It stores new kernel to RAM, reboots the device as usual, and kernel from boot partition immediately jumps to the one which was stored to RAM before reboot.
Unlike grouper's kexec-hardboot patch, this one only requires the host kernel to be patched. This is one of the improvements I made, and I think it is pretty significant.
To sumarize the process:
- kexec --load-hardboot.... is called and kernel it loaded into RAM.
- kexec -e is called. Special info is written to memory (to area which is not overwritten on reboot) and the device is rebooted.
- After reboot, very early in the boot process, kernel checks if that special info is present in RAM and if so, it loads new kernel from RAM and jumps to it.
- Kexecd' kernel starts and boots.
- Download kexec-hardboot-yuga.zip and unzip it
- Flash my patched host kernel (kexec-kernel-20140808-yuga.zip)
- Push initrd.img, kexec, kexec.sh and zImage to /cache
- Use a terminal to do the following:
adb shell su cd cache chmod 0755 kexec sh ./kexec.sh
Kexec-hardboot patch for Sony Xperia Z, Tool/Utility for the Sony Xperia Z
Last Updated 2014-08-08