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| 1 | +# `*-unknown-hermit` |
| 2 | + |
| 3 | +**Tier: 3** |
| 4 | + |
| 5 | +The [Hermit] unikernel target allows compiling your applications into self-contained, specialized unikernel images that can be run in small virtual machines. |
| 6 | + |
| 7 | +[Hermit]: https://github.com/hermitcore |
| 8 | + |
| 9 | +Target triplets available so far: |
| 10 | + |
| 11 | +- `x86_64-unknown-hermit` |
| 12 | +- `aarch64-unknown-hermit` |
| 13 | +- `riscv64gc-unknown-hermit` |
| 14 | + |
| 15 | +## Target maintainers |
| 16 | + |
| 17 | +- Stefan Lankes ([@stlankes](https://github.com/stlankes)) |
| 18 | +- Martin Kröning ([@mkroening](https://github.com/mkroening)) |
| 19 | + |
| 20 | +## Requirements |
| 21 | + |
| 22 | +These targets only support cross-compilation. |
| 23 | +The targets do support std. |
| 24 | + |
| 25 | +When building binaries for this target, the Hermit unikernel is built from scratch. |
| 26 | +The application developer themselves specializes the target and sets corresponding expectations. |
| 27 | + |
| 28 | +The Hermit targets follow Linux's `extern "C"` calling convention. |
| 29 | + |
| 30 | +Hermit binaries have the ELF format. |
| 31 | + |
| 32 | +## Building the target |
| 33 | + |
| 34 | +You can build Rust with support for the targets by adding it to the `target` list in `config.toml`. |
| 35 | +To run the Hermit build scripts, you also have to enable your host target. |
| 36 | +The build scripts rely on `llvm-tools` and binaries are linked using `rust-lld`, so those have to be enabled as well. |
| 37 | + |
| 38 | +```toml |
| 39 | +[build] |
| 40 | +build-stage = 1 |
| 41 | +target = [ |
| 42 | + "<HOST_TARGET>", |
| 43 | + "x86_64-unknown-hermit", |
| 44 | + "aarch64-unknown-hermit", |
| 45 | + "riscv64gc-unknown-hermit", |
| 46 | +] |
| 47 | + |
| 48 | +[rust] |
| 49 | +lld = true |
| 50 | +llvm-tools = true |
| 51 | +``` |
| 52 | + |
| 53 | +## Building Rust programs |
| 54 | + |
| 55 | +Rust does not yet ship pre-compiled artifacts for these targets. |
| 56 | +To compile for these targets, you will either need to build Rust with the targets enabled |
| 57 | +(see “Building the targets” above), or build your own copy of `core` by using `build-std` or similar. |
| 58 | + |
| 59 | +Building Rust programs can be done by following the tutorial in our starter application [rusty-demo]. |
| 60 | + |
| 61 | +[rusty-demo]: https://github.com/hermitcore/rusty-demo |
| 62 | + |
| 63 | +## Testing |
| 64 | + |
| 65 | +The targets support running binaries in the form of self-contained unikernel images. |
| 66 | +These images can be chainloaded by Hermit's [loader] or hypervisor ([Uhyve]). |
| 67 | +QEMU can be used to boot Hermit binaries using the loader on any architecture. |
| 68 | +The targets do not support running the Rust test suite. |
| 69 | + |
| 70 | +[loader]: https://github.com/hermitcore/rusty-loader |
| 71 | +[Uhyve]: https://github.com/hermitcore/uhyve |
| 72 | + |
| 73 | +## Cross-compilation toolchains and C code |
| 74 | + |
| 75 | +The targets do not yet support C code and Rust code at the same time. |
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