LLVM Embedded Toolchain for Arm

This repository contains build scripts and auxiliary material for building a bare-metal LLVM based toolchain targeting Arm based on:

• clang + llvm
• lld
• libc++abi
• libc++
• compiler-rt
• picolibc (newlib in versions 14 and earlier)

Goal

The goal is to provide an LLVM based bare-metal toolchain that can target the Arm architecture family from Armv6-M and newer. The toolchain follows the ABI for the Arm Architecture and attempts to provide typical features needed for embedded and realtime operating systems.

Supported architectures

• Armv6-M
• Armv7-M
• Armv7E-M
• Armv8-M Mainline
• Armv8.1-M Mainline
• AArch64 armv8.0 (experimental)

C++ support

C++ is partially supported with the use of libc++ and libc++abi from LLVM. Features that are not supported include:

• Exceptions
• RTTI
• Multithreading

Components

The LLVM Embedded Toolchain for Arm relies on the following upstream components

Component	Link
LLVM	https://github.com/llvm/llvm-project
picolibc	https://github.com/picolibc/picolibc

Windows runtime DLLs

On Windows the toolchain also uses several DLLs that are part of the Mingw-w64 project (based on GCC):

Library	Project	Link
libstdc++-6.dll	GCC	https://gcc.gnu.org
libgcc_s_seh-1.dll	GCC	https://gcc.gnu.org
libwinpthread-1.dll	Mingw-w64	http://mingw-w64.org

License

Content of this repository is licensed under Apache-2.0. See LICENSE.txt.

The resulting binaries are covered under their respective open source licenses, see component links above.

Host platforms

The LLVM Embedded Toolchain for Arm has been built and tested on Linux/Ubuntu 18.04.5 LTS, including cross-building for Windows.

Binary packages are provided for major LLVM releases for Linux and Windows.

Getting started

Download a release of the toolchain for your platform from Github releases and extract the archive into an arbitrary directory.

Using the toolchain

To use the toolchain, on the command line you need to provide:

• A configuration file specified with --config.
• A linker script specified with -T. Default picolibcpp.ld & picolibc.ld scripts are provided and can be used directly or included from a custom linker script.

For example:

$ PATH=<install-dir>/LLVMEmbeddedToolchainForArm-<revision>/bin:$PATH
$ clang --config armv6m_soft_nofp_semihost.cfg -T picolibc.ld -o example example.c

The available configuration files can be listed using:

$ ls <install-dir>/LLVMEmbeddedToolchainForArm-<revision>/bin/*.cfg

Note: If you are using the toolchain in a shared environment with untrusted input, make sure it is sufficiently sandboxed.

Building from source

LLVM Embedded Toolchain for Arm is an open source project and thus can be built from source. Please see the Building from source guide for detailed instructions.

Providing feedback and reporting issues

Please raise an issue via Github issues.

Contributions and Pull Requests

Please see the Contribution Guide for details.