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Project Sparrow: KataOS

Sparrow is a project to build a low-power secure embeded platform for Ambient ML applications. The target platform leverages RISC-V and OpenTitan.

The Sparrow software includes a home-grown operating system named KataOS, that runs on top of seL4 and (ignoring the seL4 kernel) is written almost entirely in Rust.

This is a CAmkES project that assembles the entire KataOS. It exists outside the seL4 source trees since it contains code not intended to go to upstream seL4.

This uses the standard CAmkES build system by symlinking CMakeLists.txt and assumes the CAmkES dependencies are already installed. It also symlinks settings.cmake, and so retains the notion of "apps," which enables the build system to switch which assembly it builds using the CAMKES_APP CMake cache value. KataOS just has one app, system.

Sparrow Rust crates (what's included here).

[More software will be published as we deem it ready for sharing until eventually all of Sparrow (software and hardware designs) will be available.]

Many KataOS Rust crates are in the apps/system/components directory. Common/shared code is in kata-os-common:

  • allocator: a heap allocator built on the linked-list-allocator crate
  • camkes: support for writing CAmkES components in Rust
  • capdl: support for reading the capDL specification generated by capDL-tool
  • copyregion: a helper for temporarily mapping physical pages into a thread's VSpace
  • cspace-slot: an RAII helper for the slot-allocator
  • logger: seL4 integration with the Rust logger crate
  • model: support for processing capDL; used by the kata-os-rootserver
  • panic: an seL4-specific panic handler
  • sel4-config: build glue for seL4 kernel configuration
  • sel4-sys: seL4 system interfaces & glue
  • slot-allocator: an allocator for slots in the top-level CNode

Depending on Rust crates

To use crates from Sparrow you can reference them from a local repository or directly from GitHub using git; e.g. in a Config.toml:

kata-os-common = { path = "../system/components/kata-os-common" }
kata-os-common = { git = "https://github.com/AmbiML/sparrow-kata" }

NB: the git usage depends on cargo's support for searching for a crate named "kata-os-common" in the kata repo. When using a git dependency a git tag can be used to lock the crate version.

Note that many Sparrow crates need the seL4 kernel configuration (e.g. to know whether MCS is configured). This is handled by the kata-os-common/sel4-config crate that is used by a build.rs to import kernel configuration parameters as Cargo features. In a Cargo.toml create a features manifest with the kernel parameters you need e.g.

[features]
default = []
# Used by sel4-config to extract kernel config
CONFIG_PRINTING = []

then specify build-dependencies:

[build-dependencies]
# build.rs depends on SEL4_OUT_DIR = "${ROOTDIR}/out/kata/kernel"
sel4-config = { path = "../../kata/apps/system/components/kata-os-common/src/sel4-config" }

and use a build.rs that includes at least:

extern crate sel4_config;
use std::env;

fn main() {
    // If SEL4_OUT_DIR is not set we expect the kernel build at a fixed
    // location relative to the ROOTDIR env variable.
    println!("SEL4_OUT_DIR {:?}", env::var("SEL4_OUT_DIR"));
    let sel4_out_dir = env::var("SEL4_OUT_DIR")
        .unwrap_or_else(|_| format!("{}/out/kata/kernel", env::var("ROOTDIR").unwrap()));
    println!("sel4_out_dir {}", sel4_out_dir);

    // Dredge seL4 kernel config for settings we need as features to generate
    // correct code: e.g. CONFIG_KERNEL_MCS enables MCS support which changes
    // the system call numbering.
    let features = sel4_config::get_sel4_features(&sel4_out_dir);
    println!("features={:?}", features);
    for feature in features {
        println!("cargo:rustc-cfg=feature=\"{}\"", feature);
    }
}

Note how build.rs expects an SEL4_OUT_DIR environment variable that has the path to the top of the kernel build area. The build-sparrow.sh script sets this for you but, for example, if you choose to run ninja directly you will need it set in your environment.

Similar to SEL4_OUT_DIR the kata-os-common/src/sel4-sys crate that has the seL4 system call wrappers for Rust programs requires an SEL4_DIR envronment variable that has the path to the top of the kernel sources. This also is set by build-sparrow.sh.

Source Code Headers

Every file containing source code includes copyright and license information. For dependent / non-Google code these are inherited from the upstream repositories. If there are Google modifications you may find the Google Apache license found below.

Apache header:

Copyright 2022 Google LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.