alset0326 / kgdb-android

Patches to the Nexus 5/6 kernel source to allow KGDB over serial debug cable

kgdb-android

Kernel patches to get KGDB working on the Nexus 5.

For background, please see associated blog post at http://www.contextis.com/resources/blog/kgdb-android-debugging-kernel-boss

0. Root your Nexus 5!

1. Download the stock Nexus 5 kernel (kernel/msm) using instructions from https://source.android.com/source/building.html, and then cd msm

2. Run git checkout 7717f76 to switch to the proper kernel version

3. Download this repo

4. Run git apply ./path/to/nexus5-7717f76-kgdb-patch to apply patch

5. Run make hammerhead_defconfig to create .config file

6. Copy .config from this repo to replace the one in the msm directory. Or you can Run make menuconfig to enable CONFIG_KGDB and CONFIG_KGDB_SERIAL_CONSOLE options, modify option CONFIG_STRICT_MEMORY_RWX to n.

7. Run make to build your kernel source.

8. Create your boot image, passing console arguments (IMPORTENT!)

   abootimg -u boot.img -k zImage-dtb -c 'cmdline=console=ttyHSL0,115200,n8 androidboot.console=ttyHSL0 kgdboc=ttyHSL0,115200 kgdbretry=4 androidboot.hardware=hammerhead user_debug=31 maxcpus=2 msm_watchdog_v2.enable=0'

9. Boot your phone into the bootloader (adb reboot bootloader)

10. Plug in your debug cable (see blog)

11. Boot or flash your image e.g. fastboot flash boot boot.img

12. Open a shell (adb shell), su to root, then type:

    echo -n g > /proc/sysrq-trigger

13. Hit enter

14. On your host machine fire up GDB (you'll need a working version of GDB cross-compiled for ARM):

    arm-eabi-gdb ./vmlinux
    (gdb) set remoteflow off
    (gdb) set remotebaud 115200   # or use 'set serial baud 115200' after gdb7.7
    (gdb) target remote /dev/ttyUSB0

You should hit the KGDB breakpoint and be able to continue, examine memory, etc.