Linux Development Environment

This repository contains one workflow for building and modifying the Linux kernel. It consists of two main components. The first is a docker container that contains all the requirements to build the Linux kernel, as well as the requirements to run QEMU. The second is a QEMU script that boots a virtual machine running a custom version of the Linux kernel. Using these together allows you to easily make and test changes to the Linux kernel without needing to manage all the packages locally.

This repository is cloned and modified from rosalab@Virginia Tech

Build Docker Container

make docker

Update git submodules

The linux directory contains a forked linux kernel source tree as a git submodule. The below commands help you to update it.

git submodule init

# This will take some time.
git submodule update

Update remote urls for linux

Update your own forks

git remote set-url origin [email protected]:torvalds/linux.git
git remote -v
git remote add bpf [email protected]:kernel-patches/bpf.git
git remote -v

Copy config file to linux folder

cp linux-config/.config ./linux Feel free to make changes to the config based on the usecase

Build linux

make vmlinux

Run Qemu

make qemu-run

If you want to ssh into the qemu

make qemu-ssh

If you want to enter the docker container where qemu is running

make enter-docker

If you want to debug the kernel using gdb

In an another terminal

cd linux
gdb vmlinux
target remote:1234
c

then set your breakpoints and debug more

Adding Ports to QEMU

By default host port 52223 is connected to port 52223 inside the QEMU virtual machine. If you need to be able to connect to more than one port (or a specific port) on your custom kernel from the host, you will have to add new rules. The needed rules are in q-script/yifei-q and in the Makefile.

Makefile modifications

You must add a line that maps a host port to a Docker port. In the Makefile you must add a line -p 127.0.0.1:HOST_PORT:DOCKER_PORT This will map the host port to the docker port.

q-script modifications

You must modify the q-script to connect the DOCKER_PORT to a QEMU_PORT. In the q-script you must append a new rule. Find the line that starts with "net += -netdev user...". Then at the end of the line add the text "hostfwd=tcp::DOCKER_PORT-:QEMU_PORT"

BPF Enabled

This branch has BPF enabled. You can use make libbpf to build libbpf inside the docker container. You can use make bpftool to build bpftool inside the docker container. Both have a respective clean target to clean these.

There is also a bpf-progs directory that has a make file to make building bpf programs easy. There is a naming scheme where programs of the form *.kern.c are built as BPF objects, while programs of the form *.user.c are built as user space programs.

Running BPF sample

make qemu-run

cd bpf-progs

make

./load.user helloworld.kern.o bpf_demo &

./trigger.user
<ENTER>

bpftool prog tracelog

at this point you should be able to see the prints