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)
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.
- Armv6-M
- Armv7-M
- Armv7E-M
- Armv8-M Mainline
- Armv8.1-M Mainline
- Armv4T (experimental)
- Armv5TE (experimental)
- Armv6 (experimental, using the Armv5TE library variant)
- AArch64 armv8.0 (experimental)
C++ is partially supported with the use of libc++ and libc++abi from LLVM. Features that are not supported include:
- Exceptions
- RTTI
- Multithreading
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 |
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.
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 are provided for major LLVM releases for Linux and Windows.
Download a release of the toolchain for your platform from Github releases and extract the archive into an arbitrary directory.
On Ubuntu 20.04 and later libtinfo5
is required: apt install libtinfo5
.
(This requirement will be removed in LLVM Embedded Toolchain for Arm 17.)
Prior to LLVM Embedded Toolchain for Arm 17, on macOS the toolchain binaries are quarantined by com.apple.quarantine. To run the executables change directory to bin and run the following command to remove the com.apple.quarantine:
find . -type f -perm +0111 | xargs xattr -d com.apple.quarantine
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.
- Disabling C++ exceptions and RTTI that are not supported by the standard library provided yet.
- The C runtime library: either
crt0
orcrt0-semihost
. - The semihosting library, if using
crt0-semihost
. - A linker script specified with
-T
. Defaultpicolibcpp.ld
andpicolibc.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 \
--target=armv6m-none-eabi \
-fno-exceptions \
-fno-rtti \
-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=<install-dir>/LLVMEmbeddedToolchainForArm-<revision>/lib/clang-runtimes/arm-none-eabi/armv6m_soft_nofp \
--target=armv6m-none-eabi \
-fno-exceptions \
-fno-rtti \
-lcrt0-semihost \
-lsemihost \
-T picolibc.ld \
-o example example.c
See Migrating from Arm GNU Toolchain for advice on using LLVM Embedded Toolchain for Arm with existing projects relying on the Arm GNU Toolchain.
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.
Please raise an issue via Github issues.
Please see the Contribution Guide for details.