Greenforce Clang

Greenforce Clang is an LLVM toolchain designed to simplify Linux kernel compilation, particularly for Android. This toolchain is customized to reduce reliance on AOSP binutils and offer a more flexible developer experience.

Host Compatibility

This toolchain is built on Ubuntu using the default glibc version. Compatibility with older distributions is not guaranteed. Other libc implementations (such as musl) are currently not supported.

Installation

To install and initialize Greenforce Clang on your server, run the following command:

bash <(wget -qO- https://raw.githubusercontent.com/greenforce-project/greenforce_clang/refs/heads/main/get_clang.sh)

Ensure the toolchain is included in your PATH:

export PATH="$(pwd)/greenforce-clang/bin:$PATH"

Building Linux

For an AArch64 cross-compilation setup, the following variables must be set. While some can be defined as environment variables, it is highly recommended to pass all of them directly to make to avoid unexpected behavior:

• CC=clang (must be passed directly to make)
• CROSS_COMPILE=aarch64-linux-gnu-
• For 32-bit vDSO: CROSS_COMPILE_ARM32=arm-linux-gnueabi-

Optionally, you may use LLVM-based tools to minimize reliance on GNU binutils:

• AR=llvm-ar
• NM=llvm-nm
• OBJCOPY=llvm-objcopy
• OBJDUMP=llvm-objdump
• STRIP=llvm-strip

To leverage Clang's integrated assembler and LLVM's linker (lld), you can enable the following build options:

• LLVM:1 (Use Clang and LLVM tools e.g., clang, lld instead of GNU tools.)
• LLVM_IAS:1 (Use Clang's built-in assembler instead of GNU as.(

Note: Some older kernel versions or architectures may not be fully compatible with the integrated assembler. Disable LLVM_IAS or apply necessary patches if build errors occur.

Older Android kernels (pre-4.14) require specific patches to be built with any Clang-based toolchain. Refer to android-kernel-clang for guidance.

For Android kernels 4.19 and newer, use the upstream variable CROSS_COMPILE_COMPAT in place of CROSS_COMPILE_ARM32.

Kernel Compatibility

Greenforce Clang aims to support the latest Linux kernel versions with minimal friction. Below are notes regarding kernel version compatibility:

• Linux 5.15+: Fully supported and builds successfully with LLVM 15 or newer.
• Linux 6.1 LTS: Tested with standard configurations.
• Linux 6.6 / 6.8 (Mainline): May require patches when using lld or Clang as the integrated assembler. Falling back to GNU binutils is advised if issues arise.
• Clang’s integrated assembler is not fully compatible with all inline assembly used in the kernel. Selective use of GNU tools is recommended when needed.

Make sure all required build dependencies are installed (e.g., bc, flex, bison, libssl-dev, libncurses-dev).

Differences from Other Toolchains

Greenforce Clang is designed to be easier to use compared to toolchains like AOSP Clang. Key improvements include:

• CLANG_TRIPLE does not need to be set because we don't use AOSP binutils.
• LD_LIBRARY_PATH does not need to be set because we set library load paths in the toolchain.