The Cervus Subsystem for Linux
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.cargo Lots of work May 27, 2018
cvctl Lots of work May 27, 2018
glue glue: better mm Jun 3, 2018
src Lots of work May 27, 2018
.gitignore Init Apr 29, 2018
Cargo.toml Trace branches instead of opcodes May 4, 2018
LICENSE Add license Apr 30, 2018 Add Gitter badge Jun 1, 2018
Xargo.toml Core refactor Apr 30, 2018 Lots of work May 27, 2018
x86_64-unknown-kernel.json Refactor API impl May 20, 2018


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A WebAssembly subsystem for Linux.


What is it?

Cervus implements a WebAssembly "usermode" on top of the Linux kernel (which tries to follow the CommonWA specification), enabling wasm applications to run directly in ring 0, while still ensuring safety and security.

But why?

  • Managed execution (making it possible to perform optimizations based on tracing/partial evaluation)
  • Avoid performance overhead introduced by system calls & address space switches
  • Zero-copy I/O is possible

Things that are working and not working


  • An interpreter based on HexagonE
  • Binary translation & loading based on wasm-core
  • Most of CommonWA ("everything is a URL", file I/O, command-line arguments)
  • IPC (only broadcast supported by now, with URL prefix ipc-broadcast://)

Not working:

  • Floating point
  • JIT
  • Everything else


Kernel module


  • xargo
  • latest nightly rust
  • kernel headers
  • gnu make & gcc
sudo insmod glue/cervus.ko

Loader (cvctl)

This installs the cvload and cvrun binaries:

cd cvctl
cargo install


Cervus implements most of CommonWA (tracked at #2), whose examples can be found at cwa-rs/examples.

For example, to build and run the cat example:

sudo chmod 666 /dev/cvctl
cd cwa-rs
cargo build --target wasm32-unknown-unknown --release --example cat
cvrun target/wasm32-unknown-unknown/release/examples/cat.wasm file:///etc/lsb-release

To launch an IPC broadcast sender and then read from it:

cargo build --target wasm32-unknown-unknown --release --example broadcast_sender
cvrun target/wasm32-unknown-unknown/release/examples/broadcast_sender.wasm your_broadcast

(in another terminal)

cvrun target/wasm32-unknown-unknown/release/examples/cat.wasm ipc-broadcast://your_broadcast | dd of=/dev/null bs=4K


I'm busy with my College Entrance Examination until ~June 10, 2018, before which I cannot actively maintain this project. However, there are a few things that can be relatively easily worked on:

  • A JIT based on Cretonne

Since Cretonne supports no_std, this should be relatively easy compared to other JIT approaches.

Interface with the rest of the system by implementing the Backend trait, for which the interpreter-based backend located in src/backend/hexagon_e is a good example to start with.

  • Network API

Blocking network APIs can be added as virtual system calls.


Cervus itself has to use the GPL 2.0 license because it links to the Linux kernel. However, user code that runs on Cervus is not limited by this.