# Linux Kernel Module Cheat

### 4.3. KDB

KDB is a way to use KDB directly in your main console, without GDB.

Advantage over KGDB: you can do everything in one serial. This can actually be important if you only have one serial for both shell and .

Disadvantage: not as much functionality as GDB, especially when you use Python scripts. Notably, TODO confirm you can’t see the the kernel source code and line step as from GDB, since the kernel source is not available on guest (ah, if only debugging information supported full source, or if the kernel had a crazy mechanism to embed it).

Run QEMU as:

    ./run --kdb

This passes `kgdboc=ttyS0` to the Linux CLI, therefore using our main console. Then QEMU:

    [0]kdb> go

And now the `kdb>` prompt is responsive because it is listening to the main console.

After boot finishes, run the usual:

    ./count.sh &
    ./kgdb.sh

And you are back in KDB. Now you can count with:

    [0]kdb> bp __x64_sys_write
    [0]kdb> go
    [0]kdb> go
    [0]kdb> go
    [0]kdb> go

And you will break whenever `__x64_sys_write` is hit.

You can get see further commands with:

    [0]kdb> help

The other KDB commands allow you to step instructions, view memory, registers and some higher level kernel runtime data similar to the superior GDB Python scripts.

- KDB graphic

- KDB ARM