Debugging Android

Kernel logs

While booted into Android

1. Run dmesg as root.

Failed boot

1. Reboot into recovery and check for /proc/last_kmsg or /sys/fs/pstore/*

Userspace

Stuck at boot animation (getting regular logs)

1. (Recovery) Mount System and delete file /system/phh/secure. Reboot.

2. Connect phone to PC.

3. Run

   adb logcat -d all > logs.txt

   while on bootsplash

Override ADB authentication to capture logs during boot

1. Reboot into recovery.

2. Mount system in recovery.

3. Connect to PC.

4. Run:

   adb shell mount -o rw,remount /system_root

   adb pull /system_root/system/build.prop

5. Use a text editor to change the following props in build.prop

   ro.adb.secure=0

   ro.debuggable=1

   ro.secure=0

   persist.service.adb.enable=1

   persist.service.debuggable=1

   persist.sys.usb.config=adb

   or if GNU sed is available on your system:

   sed -i 's/^ro\.adb\.secure=.*/ro.adb.secure=0/' build.prop
   sed -i 's/^ro\.debuggable=.*/ro.debuggable=1/' build.prop
   sed -i 's/^ro\.secure=.*/ro.secure=0/' build.prop
   sed -i 's/^persist\.service\.adb\.enable=.*/persist.service.adb.enable=1/' build.prop
   sed -i 's/^persist\.service\.debuggable=.*/persist.service.debuggable=1/' build.prop
   sed -i 's/^persist\.sys\.usb\.config=.*/persist.sys.usb.config=adb/' build.prop

6. Now copy the modified build.prop to /system by running:

   adb push build.prop /system_root/system/

Pull /data/boot_lc_main.txt

1. Reboot into TWRP.
2. adb pull /data/boot_lc_main.txt (if it exists).

ADB not authorized

1. Reboot into recovery.

2. Connect to PC.

3. Run:

   Linux/Unix:

   adb push ~/.android/adbkey.pub /data/misc/adb/adb_keys

   Windows:

   adb push C:\Users\%PutHereYourUsername%\.android\adbkey.pub /data/misc/adb/adb_keys

4. Now ADB should be allowed.

Early-boot (bootloop at splash/OEM logo)

Checking pstore and last_kmsg

1. Reboot to TWRP.

2. Check

   /sys/fs/pstore/*

   /proc/last_kmsg

3. Copy logs to PC (Ex: adb pull /proc/last_kmsg lastkmsg.txt)

   Note: This only works if the kernel is built with

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

Using FBCon

FBCon enables kernel output to the display. Use this as a second to the last resort if the above mentioned methods don't work.

1. Build kernel with config options:

   CONFIG_VT=y
   CONFIG_FB_SIMPLE=y
   CONFIG_FRAMEBUFFER_CONSOLE=y
   CONDIG_DRM_FBDEV_EMULATION=y

2. Modify kernel cmdline to include

   androidboot.console=tty0 console=tty0

3. Reboot into fastboot or recovery.

4. Grab another phone, make some contraption to keep it pointed at screen.

5. Adjust exposure and focus to make the text visible.

6. Run

   adb reboot

   OR

   fastboot reboot

   depending on which mode you are in.

7. Pray that the recording is clear enough. If not, try again.

8. Import it into pc, flip it (if needed), start playing it slowed down and zoomed in.

Using UART / JTAG (or better known as Serial)

This is the ONLY WAY to grab logs if all of the aforementioned methods do not work.

This assumes your kernel has UART logging enabled, and your DTS has it enabled.

Disclaimer

I (the author), or OpenDroid are not responsible for any damage done to your board, whether it be a bad soldering job, scratched pcb, or fried board.

Prerequisites

• A gadget that does UART/TTL (for most devices)

• A multimeter

• Probes (or anything that lets you reach the UART points on the board)

• Oscilloscope (if your board has undocumented serial)

1. Find your device's points

If your device has its points documented (usually somewhere in the postmarketOS wiki), then you're in luck.

If your device doesn't have the points, you can hook an oscilloscope to any points of interest and hope that your kernel has UART output enabled by default.

2. Hooking up your hardware

Attach your probes (or solder a wire to said points, NOT RECOMMENDED!!)

Before plugging in your serial gadget, make sure you're using the right voltage AS THIS CAN FRY THE BOARD!

3. Grabbing the logs

Fire up your serial reading program. The baud rate can be either found by cmdline passed by abl/preloader (or in defconfig.) If you can't find the baud rate then 115200 may be the default.

Now, power up your device. You may see early logs from abl/lk.

If all goes well, you should be able to find the root cause of your hang. If not, you can refer to the postmarketOS wiki as serial debugging is well documented there.