Author Archives: Xi Chen

Blog is back up.

We have just moved servers, because the old server has decided to quit its day job to become a full-time potato.

Mr. Potato

Sorry for the downtimes! The new server is much faster, is close to where I live, and is by the seemingly reputable guys over at

RefOS Released!

The project I’ve been working on all year has finally been released open source!

Take a look and shoot me any bugs you find!

Original email announcement below:

Today we announce the release of the RefOS project. RefOS is an OS
personality that runs on seL4. RefOS stands for “Reference OS”, the
aspirational goal of the project, which is to provide a reference OS
personality for seL4.

RefOS is a student project built as a case study to explore more
dynamic virtual memory (VM) management systems than the typical static
systems architected on separation kernels. When compared to statically
allocated systems, a key difference (and complexity) of dynamic VM
management is relaxing the assumption that virtual memory (and memory
objects) are managed by a single task upon the microkernel (or by the
microkernel itself).

RefOS has a distributed VM framework inspired by the Sawmill VM
framework [1], though differing in the centralisation of some core
book-keeping into a single server (mainly fault forwarding and mapping
authorisation). An additional goal of the project was to create
tension between user-level and kernel-level VM primitives to enable
ongoing kernel experimentation in the area of higher-level VM

The current functionality of RefOS consists of processes, an
in-memory boot-image file server, and console support. Additionally,
some games and test applications have been ported to the system.

RefOS is available at under a
“BSD 2-Clause” license.

[1] Mohit Aron, Jochen Liedtke, Kevin Elphinstone, Yoonho Park, Trent
Jaeger, and Luke Deller. 2001. The sawmill framework for virtual
memory diversity. In Proceedings of the 6th Australasian conference on
Computer systems architecture (ACSAC ’01). IEEE Computer Society,
Washington, DC, USA, 3-10.