Porting Rust standard library: Difference between revisions

{{template:In_Progress}}

By the end you should be able to compile a project with

cargo +dev-x86_64-unknown-myos r --target x86_64-unknown-myos

===Get sources===

git clone https://github.com/rust-lang/rust

===Configuration===

# config.toml

profile = "compiler"

[rust]

incremental = true

===Adding the target===

In addition, the rust compiler must be given a path to a valid crt0 object file. Rustc does not supply a <code>_start</code> symbol of its own, and the defalt linker doesn't provide one either, so we must provide our own. (TODO: Figure out self-contained linking of the crt0).

// compiler/rustc_target/src/spec/base/myos.rs

use crate::spec::crt_objects;

}

}

// compiler/rustc_target/src/spec/targets/x86_64_unknown_myos.rs

use crate::spec::{base, PanicStrategy, Target, TargetMetadata};

}

}

--- a/compiler/rustc_target/src/spec/base/mod.rs

+++ b/compiler/rustc_target/src/spec/base/mod.rs

pub(crate) mod nto_qnx;

pub(crate) mod openbsd;

--- a/compiler/rustc_target/src/spec/mod.rs

+++ b/compiler/rustc_target/src/spec/mod.rs

+

}

--- a/compiler/rustc_target/src/spec/crt_objects.rs

+++ b/compiler/rustc_target/src/spec/crt_objects.rs

===Adapt library/std===

--- a/library/std/build.rs

+++ b/library/std/build.rs

// See src/bootstrap/src/core/build_steps/synthetic_targets.rs

|| env::var("RUSTC_BOOTSTRAP_SYNTHETIC_TARGET").is_ok()

Copy <code>library/std/src/sys/pal/unsupported</code> to <code>library/std/src/sys/pal/myos</code>.

--- a/library/std/src/sys/pal/mod.rs

+++ b/library/std/src/sys/pal/mod.rs

mod unsupported;

pub use self::unsupported::*;

===Add toolchain===

rustup toolchain link dev-x86_64-unknown-myos ~/Documents/rust/rust/build/x86_64-unknown-linux-gnu/stage2

==Making the standard library functional==

====Global statics (easiest, single-threaded only) ====

{{Warning | This WILL not work on multi-threaded systems.}}

--- a/library/std/src/sys/thread_local/mod.rs

+++ b/library/std/src/sys/thread_local/mod.rs

====Native ELF TLS (fastest)====

--- a/compiler/rustc_target/src/spec/base/myos.rs

+++ b/compiler/rustc_target/src/spec/base/myos.rs

Adding print support is fairly simple given the architecture of the PAL, and merly requires filling out the Write implementations of stdout/err in <code>stdio.rs</code>. In addition, the panic_output function shoudl be set to the desired output stream for panic messages, usually stderr.

--- a/library/std/src/sys/pal/myos/stdio.rs

+++ b/library/std/src/sys/pal/myos/stdio.rs

+ Some(Stderr::new())

}

==Runtime==

If you use a crate for the runtime (e.g. <code>myos_rt</code>), you can add it as a dependency to the standard library:

[target.'cfg(target_os = "myos")'.dependencies]

myos_rt = { version = "*", features = ["rustc-dep-of-std"] }

The <code>rustc-dep-of-std</code> feature is necessary since <code>libcore</code> et al. don't exist yet.

Modify the <code>Cargo.toml</code> of your runtime library to include the feature and propagate it up, e.g.:

[dependencies]

cfg-if = "1.0"

"cfg-if/rustc-dep-of-std"

]

Do keep in mind that the same crate with different feature flags are seen as [https://github.com/rust-lang/cargo/issues/2363 <strong>different crates</strong> by the compiler]. This means that if you any globals in the runtime crate and have a project that uses both stdlib and your runtime crate there will be two separate sets of those globals. One way to work around this is by giving these globals an explicit name with <code>#[export_name = "__rt_whatever"]</code> and weakly linking them with <code>#[linkage = "weak"]</code>.

Add <code>compiler_builtins</code> as a dependency for the crates you use in stdlib, e.g.:

[dependencies]

core = { version = "1.0.0", optional = true, package = "rustc-std-workspace-core" }

"compiler_builtins/rustc-dep-of-std", # <--

]

[[Category:Rust]]