cffs / app-helloworld-rust

How to use a rust program in unikraft?

Note that rust support in unikraft is ongoing work.

Goal

Any rust program/library that you can compile with cargo as a static library should be supported, provided that:

• it does tries to load libraries dynamically with dlopen();
• it does not issue unsupported syscalls.

I.e., most rust-only code should work, most rust wrappers around other libraries won't.

Principle

To build the rust program, we turn it into a library, that exports its main entry point as a C-callable function (see helloworld/src/lib.rs).

We complement it with a simple C main() function, that calls that entry point.

The rust library is built using the x86_64-unknown-linux-musl target, asking for a staticlib, i.e. an ar archive. By default, rustc would provide a full runtime, including the musl C library, in that static library. However, you can pass it the flag -C target-feature=-crt-static to avoid that. In the latter case, rustc will include the rust runtime, but not the C runtime it depends on. This allows us to latter link the unikraft runtime (with its musl port) instead of the rust-provided musl one. This flag can be passed through RUSTFLAGS environment variable, or through .cargo/config in your rust project (see helloworld/.cargo/config).

Once the rust components have been built as static libraries, they can be added to your unikraft project through UKALIBS-y.

How to use this example

You need to install a version of rustc more recent than 1.43.1 with the x86_64-unknown-linux-musl target:

rustup install 1.46.0
rustup default 1.46.0
rustup target add x86_64-unknown-linux-musl

You'll need the following structure and branches:

• apps/helloworld-rust, csoldani/rust
• libs/compiler-rt, csoldani/rust
• libs/libcxx, csoldani/rust
• libs/libcxxabi, staging
• libs/librust, staging
• libs/libunwind, staging
• libs/musl, ggain/features
• unikraft, fix_tls_align_issue

In apps/helloworld-rust, you'll need to do a make menuconfig. Select desired targets (linuxu or kvm) and libcxx (required by libunwind).

You should then be able to build the application with make.

If the application blocks after printing "Welcome to ", disable the ukboot banner in make menuconfig.

Limitations

The port of musl on unikraft is ongoing work, and is not fully functional. More specifically, musl uses some Linux syscalls which have not yet been re-routed through the syscall shim layer, or for which the functionality has not yet been implemented.

The KVM platform currently does not work properly, due to relocation linking problems. The Xen platform has not been tested.