Libc-rs 🦀#

All-Rust libc substrate for Linux — the vendored Eyra lineage, adopted into the monorepo.

Directory rust/libc follows the repo convention (the component being replaced); the code keeps its upstream crate identities:

Vendored crate	Role	Upstream
`origin`	Program & thread startup/shutdown in Rust (asm minimized)	sunfishcode/origin
`c-ward` (`c-scape`, `c-gull`)	ABI-compatible libc functions implemented in Rust	sunfishcode/c-ward
`eyra`	Facade crate that slides the above under `std`	sunfishcode/eyra

Not vendored: rustix (and friends) stay normal crates.io dependencies — it is the one layer that remains large and very actively maintained.

Why#

Whole-process Fe-C coverage. Rewriting doesn't eliminate danger; it converts opaque C into instrumentable unsafe Rust. With this substrate, ../fe-c checks the entire process — libc included — and the unchecked residue shrinks to syscall stubs and a few lines of asm.
The Rust-userspace trajectory. This is the libc row of the NixOS-rs plan: a userland that is Rust all the way down to the syscall.
Upstream's own reasons: whole-program LTO through the libc, the set_var soundness fix, and fully static linking that still honors the platform NSS/DNS config.

Constraints (upstream-honest)#

Nightly Rust only; Linux only (x86-64, x86, aarch64, riscv64).
No dynamic linking.
Cannot run under Miri (syscalls issued from asm are not recognized), though the code targets strict provenance and I/O safety throughout.
Contains substantial unavoidable unsafe; per upstream's own README it should not be presumed safer than mature C until proven — proving it is exactly what Fe-C case mode is for (see ../fe-c).

Provenance & licensing#

Each vendored tree carries an UPSTREAM file: repo URL, commit hash, date, local patch list. Plain source import at a pinned commit — no submodules (jj-friendly).
Upstream is quiescent, not dead: repo unarchived, last tagged release 0.16.0 (Oct 2023), sparse crates.io pushes since. Policy: adopt-and-patch here, diff upstream periodically, send patches back while it answers.
Licenses preserved verbatim: Apache-2.0 / Apache-2.0 WITH LLVM-exception / MIT, plus the upstream COPYRIGHT notice.

Usage#

Classic Eyra hookup (works with plain cargo build on the pinned nightly):

# Cargo.toml
[dependencies]
std = { package = "eyra", path = "../libc/eyra" }

// build.rs
fn main() { println!("cargo:rustc-link-arg=-nostartfiles"); }

All-from-source (the Fe-C path): -Zbuild-std + extern crate eyra; instead of the rename trick. Fully static: -C target-feature=+crt-static (experimental-relocate for static-PIE + ASLR).

Nix ❄️#

nix build .#libc-hello — smoke binary, plus -static and -static-pie variants
nix build .#libc-sysroot — the eyra-linked std as a derivation, consumed by other rust/ projects (and by fe-c-sysroot-* once P2 lands)
nix flake check: hello, static DNS resolution, upstream example subset (ripgrep/coreutils smoke), and — phase-gated — the Fe-C case-mode build
Shares the repo-wide pinned nightly with ../fe-c.

Status#

Pre-vendor. See PLAN.md for the import procedure and bring-up phases.

Monorepo table row:

| [Libc-rs 🦀](https://tangled.org/@overby.me/overby.me/tree/main/rust/libc) | All-Rust libc substrate (vendored Eyra/origin/c-ward lineage) |

Configure Feed