The LLVM C Library

LLVM-libc is a from-scratch implementation of the C standard library, built as part of the LLVM project. It is designed to be modular (any piece can be used independently), multiplatform (Linux, GPU, baremetal embedded, UEFI, macOS, Windows), and written in modern C++ for correctness, performance, and safety.

What Works Today

LLVM-libc is actively used in production for a targeted set of use cases, though coverage is still growing and many programs that depend on the full C standard library (regex, locale, wide-character I/O, etc.) will not yet compile against it:

• Static-linked Linux servers and containers — used in production at Google (servers and Pixel Buds) on x86-64 and AArch64.
• GPU compute (AMDGPU, NVPTX) — libc functions available in GPU kernels via LLVM's offloading runtime. {doc}GPU docs <gpu/index>
• Baremetal embedded (ARM, RISC-V, AArch64) — minimal footprint builds for microcontrollers and custom hardware.
• UEFI applications — experimental support for firmware development. {doc}UEFI docs <uefi/index>
• LLVM ecosystem internals — libc++ and the offloading runtime consume LLVM-libc directly via {doc}Hand-in-Hand <hand_in_hand>.
• Toolchain integrations — pieces of LLVM-libc are used in Android Bionic, Fuchsia, Emscripten, and the ARM embedded toolchain.

Coverage is still growing. See the {doc}implementation status <headers/index> pages for per-header detail, and the {doc}platform support <platform_support> page for OS/architecture coverage.

Getting Started

If you are new to LLVM-libc, {doc}getting_started is the right first stop. It covers cloning, building, testing, and verifying your installation in one place.

Want to use LLVM-libc alongside your system libc instead of replacing it? See {doc}overlay_mode.

Get Involved

LLVM-libc is an active project and welcomes contributors of all experience levels. See {doc}contributing to learn how to help.

• Source code
• Bug reports
• Discourse
• Discord (invite)
• Buildbot

:caption: Using LLVM-libc
:hidden: true
:maxdepth: 1

getting_started
build_concepts
overlay_mode
full_host_build
full_cross_build
configure
hand_in_hand

:caption: Platforms
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:maxdepth: 1

gpu/index
uefi/index

:caption: Implementation Status
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:maxdepth: 1

headers/index
arch_support
platform_support
compiler_support

:caption: Development
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:maxdepth: 1

contributing
build_and_test
dev/index
porting
Maintainers

:caption: Links
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:maxdepth: 1

talks
Source Code <https://github.com/llvm/llvm-project/tree/main/libc>
Bug Reports <https://github.com/llvm/llvm-project/labels/libc>
Discourse <https://discourse.llvm.org/c/runtimes/libc>
Join the Discord <https://discord.gg/xS7Z362>
Discord Channel <https://discord.com/channels/636084430946959380/636732994891284500>
Buildbot <https://lab.llvm.org/buildbot/#/builders?tags=libc>