# GDB Debugging

## Compile a correct Linux kernel

Clone a Linux tree and run `make ARCH=arm defconfig` to make a generic kernel configuration suited for qemu. Now edit the kernel configuration (`.config`) and add the following lines at the bottom:

```
CONFIG_DEBUG_INFO=y
CONFIG_GDB_SCRIPTS=y
```

Now run `make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j$(nproc)` to compile the kernel. If you get asked about anything, just press enter to use the standard value.

Copy the output zImage (`arch/arm/boot/zImage`) to `efi/boot/bootarm.efi` on your EFI partition folder in your qemu directory.

## Prepare GDB for debugging

### Install

Run `sudo apt-get install gdb-multiarch` to install GDB on Ubuntu. `gdb-mutliarch` is required because normal `gdb` package doesn't have support for ARM.

### Run

Open up the terminal you want GDB to run in, and change directory to your Linux compilation directory. Then run `gdb-multiarch vmlinux`., it will open GDB you and you can now connect to a target with `target remote localhost:1234`. At this point GDB will wait for qemu to start. After that you can now debug with qemu, there are tutorials online to show you how to do this.

## Run qemu

Go to the directory where your qemu files are located, start qemu as described in [Qemu emulation](https://open-rt.gitbook.io/open-surfacert/development/please-read/leander-devnotes/efi-linux-booting/qemu-emulation/..#run-qemu), only change is that you need to add a `-s` parameter, this lets qemu know that it starts a GDB server.