pstore

see also ​https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/ramoops.rst

do debug the boot process the pstore driver is used to create a persitant storage area that survives boot.

The principle idea is:

• boot the boot image that you want to debug and write the boot log to pstore
• generate a kernel panic
• boot a recovery boot image that also has pstore enabled to analyze the log

In the TWRP recovery image for the chiron pstore is enabled and pstore is automatically mounted to /sys/fs/pstore/

Kernel

The following options have to be enabled in the kernel config (in both boot images)

CONFIG_PSTORE=y
CONFIG_PSTORE_CONSOLE=y
CONFIG_PSTORE_PMSG=y
CONFIG_PSTORE_RAM=y

Mounting pstore

To read the info in pstore it has to be mounted (in the boot image that is used to analyze the pstore) with something like

mount -t pstore pstore /sys/fs/pstore

In the TWRP recovery image for the chiron pstore is automatically mounted to /sys/fs/pstore/

Writing to pstore

When CONFIG_PSTORE_PMSG is enabled it defines a device /dev/pmsg0 to which one can write messages

echo "Hello Guhl" > /dev/pmsg0

After the kernel panic and reboot the result should be in /sys/fs/pstore/pmsg-ramoops-X

Kernel panic

For what ever reason the standard way to generate a kernel panic

echo c > /proc/sysrq-trigger

did not work for me so I created a kernel module that I can insmod to generate a panic.

I am using the attached kernel module to create a kernel panic (modprobe the module)

See also ​https://github.com/guhl/android_kernel_xiaomi_msm8998-1/commit/50c8d7f1ba19002b6743b96b6ce043470e4bbb87

The files are placed in a directory "panic" in the kernel directory and enabled in kernel config with

CONFIG_GUHL_PANIC=m

In addition the following line has to be added to the Makefile in the kernel directory.

obj-y += panic/

and the following line has to be added to the to the Kconfig in the root of the kernel directory

source "kernel/panic/Kconfig"

Kernel panic in boot image

To use the kernel panic in the boot image it has to be added to the initramfs.

See ​https://github.com/guhl/hybris-boot_chiron/commit/3dc13787ed18abcd1a9f76c81a67d1e489603320

Changes in hybris/hybris-boot/Android.mk

• define a variable for the panic module (next to BB_STATIC)

  PM_STATIC := $(PRODUCT_OUT)/vendor/lib/modules/panic.ko
  

• copy the PM_STATIC to the /bin directory (next to "@cp $(BB_STATIC) $(BOOT_INTERMEDIATE)/initramfs/bin/")

  @cp $(PM_STATIC) $(BOOT_INTERMEDIATE)/initramfs/bin/
  

Usage in init

See also ​https://github.com/guhl/hybris-boot_chiron/commit/3dc13787ed18abcd1a9f76c81a67d1e489603320

To write to pstore and cause a kernel panic add something like

    # first test of pstore / panic
    cat /init.log > /dev/pmsg0
    /bin/busybox insmod /bin/panic.ko

to hybris/hybris-boot/init-script where ever you want to see the init.log or output additional information.

Then build the boot image using make hybrs-boot in HABUILD and boot it using fastboot boot. After the kernel panic and the reboot boot to recovery or LOS and check the files in /sys/fs/pstore

/sys/fs/pstore/console-ramoops-0 and /sys/fs/pstore/dmesg-ramoops-0 should contain

<0>[    3.596679] Kernel panic - not syncing: Guhl caused a kernel panic!

/sys/fs/pstore/pmsg-ramoops-0 should contain the init.log of mer and look something like

+ exec
+ echo Running Mer Boat Loader
Running Mer Boat Loader
+ BOOTLOGO=
+ ALWAYSDEBUG=
+ DATA_PARTITION=/dev/sda17
+ DEFAULT_OS=sailfishos
+ export PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin
+ USB_FUNCTIONS=rndis
+ ANDROID_USB=/sys/class/android_usb/android0
+ GADGET_DIR=/config/usb_gadget
+ LOCAL_IP=192.168.2.15
+ DONE_SWITCH=no
+ [ /init = /init-debug ]
+ [ no = no ]
+ EXPLICIT_BUSYBOX=
+ TELNET_DEBUG_PORT=23
+ /bin/busybox --install -s
+ date
Sat Nov 28 00:15:15 UTC 1970
+ do_mount_devprocsys
+ echo ########################## mounting devprocsys
########################## mounting devprocsys
+ mkdir /dev
mkdir: can't create directory '/dev': File exists
+ mount -t devtmpfs devtmpfs /dev
+ mkdir /dev/pts
+ mount -t devpts devpts /dev/pts
+ mkdir /proc
+ mkdir /sys
+ mount -t sysfs sysfs /sys
+ mount -t proc proc /proc
+ mkdir /config
+ mount -t configfs none /config
+ do_hotplug_scan
+ echo /sbin/mdev
+ mdev -s
+ sleep 2
+ cat /init.log