Development kernel for kernel developers

[tom3q]

--- This shouldn't be specially dangerous, but as usual: ---
WARNING: THIS METHOD CAN BE DANGEROUS. DON’T DO ANYTHING IF YOU DO NOT KNOW WHAT YOU DO.
I AM NOT RESPONSIBLE IF YOU TRANSFORM YOUR SPICA INTO A BRICK

I've made a specially prepared kernel to allow testing new kernels without flashing, using kexec.

Features:

• kexec inside the initramfs
• no recovery utility, just kernel output on the screen (ADB still available)
• always boots to recovery
• screen is kept enabled on kernel shutdown (kexec shuts the old kernel down first)

Bugs: (will be probably tracked down and fixed in some near future)

• CPU frequency has to be changed to 400 MHz or less before running kexec.(ie. echo 400000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq)

Usage:

1. Flash the development kernel
2. Upload new kernel to your phone (preferably with adb push and to /tmp)
3. Limit CPU frequency (echo 400000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq)
4. Load the kernel with kexec -l kernel_image
5. Boot the kernel with kexec -e

Notes:

• Kernel can be flashed to the phone by issuing the following command in adb shell:
  

  bml_flash boot kernel_image

  where kernel_image is the path to the kernel located somewhere on the phone (in /tmp preferably)
• If you want to make your own kernel supporting kexec, gunzip the attached kexec.gz file, put it in /sbin of your initramfs source tree, enable "kexec system call" support in your kernel configuration and rebuild it.
• utils.tar.gz contains physical memory manipulation utilities to allow dumping and modification of RAM contents, for example android ram console data.

[LeshaK]

allow testing new kernels without flashing, using kexec.

THANK YOU!!!

[darth_llamah]

For which Android is it?

[tom3q]

Any. It's not supposed to boot Android, only a special recovery terminal to load another kernel.

[criminal]

How can I dump dmesg into screen?
I've disabled log and progress bar, enabled framebuffer console, 4x6 mini font...
I've got android text (and reset, which I need to debug)

[tom3q]

It depends on kernel version, but generally you have to bypass the command line passed by the bootloader, which says that the console should go to ttyS2, which is a serial port.

In 2.6.29 you have to open arch/arm/kernel/setup.c and comment a call to strlcpy in parse_tag_cmdline, in newer kernels there is an option in config for that. Then independently of kernel version you have to edit the built-in command line (in config) to include console=tty1 instead of ttyS2* .

[criminal]

Thanks, it's working... Now, I need to read it fast I saw somewhere a settings some timeout before reset

[tom3q]

If the reset is caused by a kernel panic then you can set the panic timeout value by appending "panic=XX" to the kernel command line, where XX is the timeout value in seconds.