Badger Kernel is a kernel providing multithreading on Arm platforms. (Badger because badgers have stripes and stripes are vaguely like threads)

A minimal userspace is included to show how to use the kernel and test its functionality. There is no filesystem, this is provided by semihosting.

Current targets are:

• Arm (Armv7A Cortex A-15 virt)
• Thumb (Armv7E-M Cortex-M4)
• AArch64 (Cortex A-57 virt, Raspberry Pi 4)

For implementation details see the design doc.

Features

• Cooperative multitasking
• Timer based thread switching
• Loading ELF programs, including position independent code
• Message passing
• Mutexes and condition variables
• Thread local storage
• Memory allocation
• File handling (via semihosting)
• Signal handling
• Permissions and errno for error handling
• Access to thread registers for tracing
• User space threads (fibers)
• Stack under/overflow detection

Building

Install cmake, make and an arm-none-eabi or aarch64-none-elf toolchain. Arm developer releases are the best way to get these.

AArch64:

https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-a/downloads

Arm/Thumb:

https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm/downloads

Install QEMU with Arm support (comes with AArch64 as well):

sudo apt-get install qemu-system-arm

See the CI config for the currently tested versions of all of the tools.

Then configure and build according to which toolchain you installed:

cmake . -DBUILD_PLATFORM=aarch64
<or>
cmake . -DBUILD_PLATFORM=arm
<or>
cmake . -DBUILD_PLATFORM=thumb

make

Demos

Demos are how we test Badger Kernel. For example, to run the yielding demo:

make run_yielding

Each demo has run_<demo>, debug_<demo> and test_<demo> make targets.

To test all the demos use lit (https://pypi.org/project/lit/) or just run make.

For a full list see the demos.md.

Shell

There is a interactive shell, do make run_shell to use it. There's some basic commands provided and it can run loadable programs as commands. (see demos/shell for examples)

--------------------
----- BK Shell -----
--------------------
$ help
Builtins:
help quit run
Programs:
echo ps ls
$ echo hello BK
hello BK
$ run ps
|-----------|
| Thread 0
|-----------|
| Name      | shell
| State     | suspended (2)
| Child     | run (1)
|-----------|
|-----------|
| Thread 1
|-----------|
| Name      | run
| State     | suspended (2)
| Child     | ps (2)
|-----------|
|-----------|
| Thread 2
|-----------|
| Name      | ps
| State     | running (1)
|-----------|