Cross-Compilation, `x` Commands, Cleaning, and Disk Space

target = ["x86_64-unknown-linux-gnu", "wasm32-wasip1"] ``` Note that building for some targets requires having external dependencies installed (e.g. building musl targets requires a local copy of musl). Any target-specific configuration (e.g. the path to a local copy of musl) will need to be provided by your `bootstrap.toml`. Please see `bootstrap.example.toml` for information on target-specific configuration keys. For examples of the complete configuration necessary to build a target, please visit [the rustc book](https://doc.rust-lang.org/rustc/platform-support.html), select any target under the "Platform Support" heading on the left, and see the section related to building a compiler for that target. For targets without a corresponding page in the rustc book, it may be useful to [inspect the Dockerfiles](../tests/docker.md) that the Rust infrastructure itself uses to set up and configure cross-compilation. If you have followed the directions from the prior section on creating a rustup toolchain, then once you have built your compiler you will be able to use it to cross-compile like so: ```bash cargo +stage1 build --target wasm32-wasip1 ``` ## Other `x` commands Here are a few other useful `x` commands. We'll cover some of them in detail in other sections: - Building things: - `./x build` – builds everything using the stage 1 compiler, not just up to `std` - `./x build --stage 2` – builds everything with the stage 2 compiler including `rustdoc` - Running tests (see the [section on running tests](../tests/running.html) for more details): - `./x test library/std` – runs the unit tests and integration tests from `std` - `./x test tests/ui` – runs the `ui` test suite - `./x test tests/ui/const-generics` - runs all the tests in the `const-generics/` subdirectory of the `ui` test suite - `./x test tests/ui/const-generics/const-types.rs` - runs the single test `const-types.rs` from the `ui` test suite ### Cleaning out build directories Sometimes you need to start fresh, but this is normally not the case. If you need to run this then bootstrap is most likely not acting right and you should file a bug as to what is going wrong. If you do need to clean everything up then you only need to run one command! ```bash ./x clean ``` `rm -rf build` works too, but then you have to rebuild LLVM, which can take a long time even on fast computers. ## Remarks on disk space Building the compiler (especially if beyond stage 1) can require significant amounts of free disk space, possibly around 100GB. This is compounded if you have a separate build directory for rust-analyzer (e.g. `build-rust-analyzer`). This is easy to hit with dev-desktops which have a [set disk quota](https://github.com/rust-lang/simpleinfra/blob/8a59e4faeb75a09b072671c74a7cb70160ebef50/ansible/roles/dev-desktop/defaults/main.yml#L7) for each user, but this also applies to local development as well. Occasionally, you may need to: - Remove `build/` directory. - Remove `build-rust-analyzer/` directory (if you have a separate rust-analyzer build directory). - Uninstall unnecessary toolchains if you use `cargo-bisect-rustc`. You can check which toolchains are installed with `rustup toolchain list`.

The text discusses configuring build targets in `bootstrap.toml` and the external dependencies needed for certain targets, referencing the `rustc` book and Dockerfiles for configuration examples. It then covers using the built compiler for cross-compilation and introduces other useful `x` commands for building and testing. The section details the `x clean` command for removing build directories, advising caution in its use. Finally, it highlights the significant disk space requirements for building the compiler, especially beyond stage 1, and provides tips for freeing up space, such as removing build directories and uninstalling unnecessary toolchains.