The LLVM C Library


The libc is not complete. If you need a fully functioning C library right now, you should continue to use your standard system libraries.


The libc aspires to a unique place in the software ecosystem. The goals are:

  • Fully compliant with current C standards (C17 and upcoming C2x) and POSIX.

  • Easily decomposed and embedded: Supplement or replace system C library functionality easily. This is useful to get consistent math precision across systems, or updated memory operations for newer microarchitectures. These pieces will work on Linux, MacOS, Windows, and Fuchsia.

  • The creation of fully static binaries without license implications.

  • Increase whole program optimization opportunities for static binaries through ability to inline math and memory operations.

  • Reduce coding errors by coding in modern C++ through the use of lightweight containers during coding that can be optimized away at runtime.

  • Permit fuzzing and sanitizer instrumentation of user binaries including the libc functions.

  • A complete testsuite that tests both the public interface and internal algorithms.

  • Fuzzing

Platform Support

Most development is currently targeting x86_64 and aarch64 on Linux. Several functions in the libc have been tested on Windows. The Fuchsia platform is slowly replacing functions from its bundled libc with functions from this project.

ABI Compatibility

The libc is written to be ABI independent. Interfaces are generated using LLVM’s tablegen, so supporting arbitrary ABIs is possible. In it’s initial stages there is no ABI stability in any form.