The Little Kernel Embedded Operating System

The LK kernel is an SMP-aware kernel designed for small systems ported to a variety of platforms and cpu architectures.

See https://github.com/littlekernel/lk for the latest version.

High Level Features

• Fully-reentrant multi-threaded preemptive kernel
• Portable to many 32 and 64 bit architectures
• Support for wide variety of embedded and larger platforms
• Powerful modular build system
• Large number of utility components selectable at build time

Supported architectures

• ARM32
  • Cortex-M class cores (armv6m - armv8m)
  • ARMv7+ Cortex-A class cores
• ARM64
  • ARMv8 and ARMv9 cores
• RISC-V 32 and 64bit bit in machine and supervisor mode
• x86-32 and x86-64
• Motorola 68000
• Microblaze
• MIPS
• OpenRISC 1000
• VAX (experimental)

TODO

To build and test for ARM64 on linux

1. install or build qemu. v2.4 and above is recommended.
2. install gcc for arm64 (see note 1)
3. run scripts/do-qemuarm -6 (from the lk directory)
4. you should see 'welcome to lk/MP'

This will get you a interactive prompt into LK which is running in qemu arm64 machine 'virt' emulation. type 'help' for commands.

Note: for ubuntu x86-64 sudo apt-get install gcc-aarch64-linux-gnu or fetch a prebuilt toolchain from https://newos.org/toolchains/aarch64-elf-14.1.0-Linux-x86_64.tar.xz

Building with LLVM-based toolchains

To build LK with a LLVM-based toolchain you will have to manually specify the compiler and linker in the environemnt. Unlike GCC clang is a cross-compiler by default, so the target needs to be specified as part of the CC/CXX/CPP variables. For example, assuming LLVM is in /opt/llvm/bin/, the following command will work to build for 64-bit RISC-V:

gmake qemu-virt-riscv64-test 'CC=/opt/llvm/bin/clang --target=riscv64-unknown-elf' 'CPP=/opt/llvm/bin/clang-cpp --target=riscv64-unknown-elf' 'CXX=/opt/llvm/bin/clang++ --target=riscv64-unknown-elf' 'LD=/opt/llvm/bin/ld.lld' TOOLCHAIN_PREFIX=/opt/llvm/bin/llvm- CPPFILT=/opt/llvm/bin/llvm-cxxfilt

TOOLCHAIN_PREFIX can be set to use the LLVM binutils, but due to the different naming of llvm-cxxfilt vs c++filt it needs to be set explicitly.

To build for AArch64 the command looks similar, just with a different --target= flag.

gmake qemu-virt-arm64-test 'CC=/opt/llvm/bin/clang --target=aarch64-unknown-elf' 'CPP=/opt/llvm/bin/clang-cpp --target=aarch64-unknown-elf' 'CXX=/opt/llvm/bin/clang++ --target=aarch64-unknown-elf' 'LD=/opt/llvm/bin/ld.lld' TOOLCHAIN_PREFIX=/opt/llvm/bin/llvm- CPPFILT=/opt/llvm/bin/llvm-cxxfilt