Cosix

Cosix is a fully capability-based operating system. It is written from scratch and consists of a small kernel that provides memory management and inter-process communication, and a userland that provides an IP stack and filesystems. It runs only on x86, but there are plans to support x86-64 and arm7 in future releases.

The capability enforcing mechanism comes from implementing only CloudABI[0] as an Application Binary Interface between the userland and the kernel. CloudABI takes POSIX, adds capability-based security, and removes everything that's incompatible with that. For more information, see https://nuxi.nl/.

Cosix has been tested on bochs, qemu and VirtualBox. Notably, it has not been tested on real hardware yet.

[0] http://nuxi.nl/cloudabi

How to build it

To compile the Cosix world including the kernel, you need the following dependencies:

• A supported linker, choose either:
  • The GNU linker with x86 support. If you build binutils with --target i686 you'll have it as i686-elf-ld which is the default name CMake looks for. If your GNU ld is named differently, just give -DCMAKE_GLD_LINKER=ld.
  • The LLVM linker (ldd). Set -DCMAKE_GLD_LINKER=ld.ldd to find it.
• An objcopy binary with x86 support, including llvm-objcopy. The build looks for a binary called objcopy but does not check early if it has x86 support. If you get objcopy-related errors, try giving -DCMAKE_OBJCOPY=llvm-objcopy or build binutils with --target i686 and use -DCMAKE_OBJCOPY=i686-elf-objcopy.
• Tools to build a disk image: sfdisk or fdisk, qemu-img, genext2fs and dd.
• The CloudABI toolchain, see instructions at https://nuxi.nl/. The toolchain is based on Clang/LLVM and is available for many operating systems. After installation, you'll have Clang in your path as i686-unknown-cloudabi-cc.
• At least the following CloudABI ports packages:
  • i686-unknown-cloudabi-cxx-runtime
  • i686-unknown-cloudabi-libircclient
  • i686-unknown-cloudabi-mstd
  • i686-unknown-cloudabi-python
  • i686-unknown-cloudabi-flower

Other compile flags to use:

• -DCLOUDABI_PYTHON_BINARY and -DCLOUDABI_PYTHON_LIBRARIES. The initrd cannot be built without CloudABI Python, so the make boot target cannot be run without this. Use the two flags, with absolute directories to the Python3 binary and its libraries, to be able to boot.
• -DCLOUDABI_FLOWER_SWITCHBOARD_BINARY. As above, this is a necessary dependency to run Cosix.
• -DCLOUDABI_UNITTEST_BINARY can be pointed at the unittest binary of cloudlibc, so you can run it by entering run_unittests() at the Python shell. Note that because not all system calls are (fully) implemented, the default binary will have a lot of failing tests.

Use the i686-elf toolchain file to set up your build directory for a native build easily:

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Debug \
 -DCMAKE_TOOLCHAIN_FILE=../cmake/Toolchain-i686-elf.cmake \
 -DCLOUDABI_PYTHON_BINARY=... \
 -DCLOUDABI_PYTHON_LIBRARIES=... \
 ..
make

There are various targets to build or run the kernel in various ways:

boot      - run inside qemu
fastboot  - run inside qemu, don't build first
gdbboot   - run inside qemu with -S -s, i.e. wait for debugger to attach
iso       - build an ISO file using mkisofs/genisoimage/xorriso
isoboot   - boot ISO using qemu
bochsboot - run inside bochs

Once it's running, it will try to get a DHCP lease and start listening on TCP port 26. In the default qemu configuration, host port 2626 is forwarded to this port. Once you connect you'll be presented with a Python shell with these useful utility commands (implemented in misc/python):

this_conn(): gives a Socket object to your current connection
rm_rf(name, dir_fd): recursively removes the given name from the directory fd
run_unittests(): run the CloudABI unittests exactly once, with 1 thread
run_unittests_count(count): run the unittests $count times
run_leak_analysis(): run the unittests 4 times, then present kernel memory leak analysis
run_tests(): run all userland binary tests and the unittests once

Unit tests

To run the native tests, compile cosix with a native compiler:

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Debug ..
make
make test

Note that the unit test suite is all but complete. Tests with better coverage are available as userland binaries that can be started when the kernel is running.

Author & contributors

See the LICENSE file for license information.

Author: Sjors Gielen sjors@sjorsgielen.nl