Setup Windbg KdCom

Tips

Suggest using KdNet for better experience if you can not access your device's uart pins easily.
KdCom does not support rdp over it.

Preparation

• A dev board, or any device with uart test points
• An UART->USB bridge, or on board bridge.(Notice: Qualcomm use 1.8V as VDDIO)
• Debugging slave installed windows
• Debugging host installed Windbg Preview

Setup BCD

• Mount ESP Partition on your phone with root permission in adb shell or termux.
  • Simply jump this step if you are using USB mass storage mode.

  # Execute on phone
  mkdir /dev/esp_mnt
  mount /dev/block/by-name/esp /dev/esp_mnt

• Copy BCD to your host computer.
  • If you are using UMS, find the BCD file and copy it to D: or anywhere you want in explorer.
  • Copy to /sdcard

  # Execute on phone
  cp /dev/esp_mnt/EFI/Microsoft/Boot/BCD /sdcard

  • Pull to computer.

  # Execute on computer, assuming installed adb.
  # Assuming copy to D:, you can set any path you want.
  adb pull /sdcard/BCD D:\

• Open an administrator terminal and set bcd configurations.

  cd D:\
  bcdedit /store BCD /set "{default}" testsigning on
  bcdedit /store BCD /set "{default}" nointegritychecks on
  bcdedit /store BCD /set "{default}" debug on 
  bcdedit /store BCD /dbgsettings serial baudrate:115200 debugport:1

• Push BCD back to your phone.
  • If you are using UMS, simply replace the original BCD file.

  # Execute on computer
  adb push BCD /sdcard
  # Delete BCD after pushing
  del D:\BCD

  # Execute on phone
  # Backup normal BCD
  cp /dev/esp_mnt/EFI/Microsoft/Boot/BCD /dev/esp_mnt/EFI/Microsoft/Boot/NMBCD
  # Backup kdnet enabled BCD
  cp /sdcard/BCD /dev/esp_mnt/EFI/Microsoft/Boot/DBGBCD
  # Replace active BCD
  cp /sdcard/BCD /dev/esp_mnt/EFI/Microsoft/Boot/BCD

Setup KdCom in Windbg

• Open device manager on your computer.
• Connect UART->USB bridge to computer, and check the COMXX Number under Serial section in device manager
• Open Windbg Preview, Click File button on the top left corner.
• Click Attach to kernel under Start debugging(default section).
• Choose COM section
  • Fill Baud Rate with 115200
  • Fill Port with COMXX, which you saw in device manager
  • Others keep default
• Click OK button and windbg will start waiting for connection.

Connect KdCom

• Ensure DBG2 configuration is correct(No need worry because the address in dbg2 was fixed generally here).
• Reboot your phone, and connect it to computer with a usb cable.

# Execute on computer, boot uefi
fastboot boot uefi.img

• Phone booting windows and hang up for several seconds, you can see windbg print logs if successfully connected.

Notice

• You can close Windbg and open a serial tool like PuTTY or SecureCRT to check if the phone printed some unrecognized messages while windows booting. If it isn't that means BCD configurations were wrong