crabc libc

crabc is a BSD-3-Clause licensed implementation of the musl C library ABI and dynamic linker for Linux, written in Rust. It runs unmodified musl-linked binaries on x86_64, aarch64 and riscv64 when libldso.so is used as the interpreter, and provides libc.a for static linking. crabc is built on the principle that a libc should be small, easy to audit and safe to maintain; unsafe is confined to syscalls and pointer glue.

crabc tracks musl 1.2.6 and exports its full public symbol surface. It is validated with musl's own libc-test and a differential harness that runs the same binaries under musl and crabc. CI also checks that every musl ABI macro is present on x86_64, aarch64 and riscv64, expands to the same tokens as musl in both C and C++, and that numeric header macros agree with the corresponding Rust constants. It is faster than musl on both x86_64 and riscv64 (qemu-user) in the microbenchmark suite; process startup is the one structural exception. See docs/performance.md.

Real, unmodified Alpine binaries are tracked in the workload matrix: BusyBox, curl, Git, SQLite, nginx, Redis, CPython, Node.js and PostgreSQL all run under crabc, with a per-project report and baseline comparison. The LTP report records the syscalls, math, memory-management, scheduler, threading and SysV IPC suites against the same binaries under musl and crabc; the shared suites have identical failure lists. Release APKs are split the same way as Alpine's musl packages: crabc (runtime), crabc-dev (headers, libc.a, Rust-built CRT objects) and crabc-utils (getconf, getent, iconv, ldd, ldconfig). See docs/packages.md. A Docker image that uses crabc as the system libc is built from docker/Dockerfile.

crabc is not the first C library written in Rust, and it is not a musl fork: it is an independent implementation tracking the musl ABI. See docs/comparison.md for how it relates to musl, relibc, eyra, and other projects.

Status and scope

crabc is experimental (0.7.x). It is not a production-ready drop-in replacement for musl. The validated scope is the workload matrix and LTP report above; functionality outside that scope is not claimed.

An earlier README overstated Rust's safety guarantees, implying that the implementation was free of buffer overflows, use-after-free, or undefined behavior. That was inaccurate. Like every libc, crabc contains unsafe code at the syscall and pointer boundary. Rust reduces the unsafe surface; it does not eliminate it. Claims in this repository are limited to what the test suites and workload matrix demonstrate.

Build and cross-compilation instructions are in AGENTS.md. Release builds are size-optimized and stripped, and are produced from v* tags; the workspace is published as the crabc, crabc-libc and crabc-ldso crates.

Documentation: comparison, workloads, LTP, performance.

crabc is licensed under BSD-3-Clause.