# LLVM-embedded-toolchain-for-Arm **Repository Path**: mirrors_ARM-software/LLVM-embedded-toolchain-for-Arm ## Basic Information - **Project Name**: LLVM-embedded-toolchain-for-Arm - **Description**: A project dedicated to building LLVM toolchain for Arm and AArch64 embedded targets. - **Primary Language**: Unknown - **License**: Apache-2.0 - **Default Branch**: main - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 1 - **Forks**: 0 - **Created**: 2020-10-13 - **Last Updated**: 2025-10-04 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README > [!WARNING] > This repository is deprecated! > > LLVM Embedded Toolchain for Arm is now > [Arm Toolchain for Embedded](https://github.com/arm/arm-toolchain/tree/arm-software/arm-software/embedded) > maintained in the unified Arm Toolchain [repository](https://github.com/arm/arm-toolchain) > hosting embedded and Linux toolchains. > > 19.1.5 is the last release of the LLVM Embedded Toolchain for Arm. > Use Arm Toolchain for Embedded [releases](https://github.com/arm/arm-toolchain/releases) for LLVM 20 and later. # 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, or optionally newlib or LLVM's libc ## 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 and Baseline - Armv8.1-M Mainline and Baseline - Armv4T (experimental) - Armv5TE (experimental) - Armv6 (experimental, using the Armv5TE library variant) - Armv7-A - Armv7-R - AArch32 Armv8-A - AArch32 Armv8-R - AArch64 Armv8-A ## C++ support C++ is partially supported with the use of libc++ and libc++abi from LLVM. Features that are not supported include: - Multithreading LLVM Embedded Toolchain for Arm uses the unstable libc++ ABI version. This ABI uses all the latest libc++ improvements and bugfixes, but may result in link errors when linking against objects compiled against older versions of the ABI. For more information see https://libcxx.llvm.org/DesignDocs/ABIVersioning.html. ## 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 ## License Content of this repository is licensed under Apache-2.0, see [LICENSE.txt](LICENSE.txt). Individual patch files under the [patches](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/tree/main/patches) folder may contain code under the upstream project license, if they are cherry-picks of upstream commits into the LLVM Embedded Toolchain for Arm release branches, see corresponding pull requests for references. The resulting binaries are covered under their respective open source licenses, see component links above. Testing for some targets uses the freely-available but not open-source Arm FVP models, which have their own licenses. These are not used by default, see [Building from source](docs/building-from-source.md) for details. ## Host platforms LLVM Embedded Toolchain for Arm is built and tested on Ubuntu 18.04 LTS. The Windows version is built on Windows Server 2019 and lightly tested on Windows 10. Building on macOS is functional for x86_64 and Apple Silicon. [Binary packages](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/releases) are provided for major LLVM releases for Linux and Windows. ## Getting started Download a release of the toolchain for your platform from [Github releases](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/releases) and extract the archive into an arbitrary directory. ### Pre-requisite for using toolchain on Windows Install appropriate latest supported Microsoft Visual C++ Redistributable package, such as from [Microsoft Visual C++ Redistributable latest supported downloads](https://learn.microsoft.com/en-us/cpp/windows/latest-supported-vc-redist?view=msvc-170). ### Using the toolchain > *Note:* If you are using the toolchain in a shared environment with untrusted input, > make sure it is sufficiently sandboxed. To use the toolchain, on the command line you need to provide the following options: * The target triple. * The FPU to use. * Disabling/enabling C++ exceptions and RTTI. * The C runtime library: either `crt0` or `crt0-semihost`. `crt0` will be linked automatically, but this can be suppressed with the `-nostartfiles` option so that `crt0-semihost` can be used. * The semihosting library, if using `crt0-semihost`. * A [linker script]( https://sourceware.org/binutils/docs/ld/Scripts.html) specified with `-T`. Default `picolibcpp.ld` and `picolibc.ld` scripts are provided and can be used directly or included from a [custom linker script]( https://github.com/picolibc/picolibc/blob/main/doc/linking.md#using-picolibcld). For example: ``` $ PATH=/LLVMEmbeddedToolchainForArm-/bin:$PATH $ clang \ --target=armv6m-none-eabi \ -mfpu=none \ -fno-exceptions \ -fno-rtti \ -nostartfiles \ -lcrt0-semihost \ -lsemihost \ -T picolibc.ld \ -o example example.c ``` `clang`'s multilib system will automatically select an appropriate set of libraries based on your compile flags. `clang` will emit a warning if no appropriate set of libraries can be found. To display the directory selected by the multilib system, add the flag `-print-multi-directory` to your `clang` command line options. To display all available multilibs run `clang` with the flag `-print-multi-lib` and a target triple like `--target=aarch64-none-elf` or `--target=arm-none-eabi`. It's possible that `clang` will choose a set of libraries that are not the ones you want to use. In this case you can bypass the multilib system by providing a `--sysroot` option specifying the directory containing the `include` and `lib` directories of the libraries you want to use. For example: ``` $ clang \ --sysroot=/LLVMEmbeddedToolchainForArm-/lib/clang-runtimes/arm-none-eabi/armv6m_soft_nofp \ --target=armv6m-none-eabi \ -mfpu=none \ -fno-exceptions \ -fno-rtti \ -nostartfiles \ -lcrt0-semihost \ -lsemihost \ -T picolibc.ld \ -o example example.c ``` The FPU selection can be skipped, but it is not recommended to as the defaults are different to GCC ones. The builds of the toolchain come packaged with two config files, Omax.cfg and OmaxLTO.cfg. When used, these config files enable several build optimisation flags to achieve highest performance on typical embedded benchmarks. OmaxLTO.cfg enables link-time optimisation (LTO) specific flags. These configs can be optionally passed using the `--config` flag. For example: ``` $ clang \ example.c \ ... --config=Omax.cfg \ --config=OmaxLTO.cfg \ -o example ``` Users should be warned that Omax.cfg enables `-ffast-math` which breaks IEEE compliance and enables maths optimisations which can affect code correctness. LTOs are kept separately in OmaxLTO.cfg as users may not want LTOs due to potential increase in link time and/or increased memory usage during linking. Some of the options in the config files are undocumented internal LLVM options. For these undocumented options please see the source code of the corresponding optimisation passes in the [LLVM project](https://github.com/llvm/llvm-project) to find out more. Users are also encouraged to create their own configs and tune their own flag parameters. Information on LLVM Embedded Toolchain for Arm specific optimization flags is available in [Optimization Flags](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/blob/main/docs/optimization-flags.md) Binary releases of the LLVM Embedded Toolchain for Arm are based on release branches of the upstream LLVM Project, thus can safely be used with all tools provided by LLVM [releases](https://github.com/llvm/llvm-project/releases) of matching version. See [Migrating from Arm GNU Toolchain](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/blob/main/docs/migrating.md) and [Experimental newlib support](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/blob/main/docs/newlib.md) for advice on using LLVM Embedded Toolchain for Arm with existing projects relying on the Arm GNU Toolchain. > *Note:* `picolibc` provides excellent > [support for Arm GNU Toolchain](https://github.com/picolibc/picolibc/blob/main/doc/using.md), > so projects that require using both Arm GNU Toolchain and LLVM Embedded Toolchain for Arm > can choose either `picolibc` or `newlib`. ## 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](docs/building-from-source.md) guide for detailed instructions. ## Providing feedback and reporting issues Please raise an issue via [Github issues](https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/issues). ## Contributions and Pull Requests Please see the [Contribution Guide](docs/contributing.md) for details.