meta-clang (a C language family frontend and LLVM compiler backend)

This layer provides clang/llvm as alternative to your system C/C++ compiler for OpenEmbedded based distributions along with gcc

Getting Started

git clone git://github.com/openembedded/openembedded-core.git
cd openembedded-core
git clone git://github.com/openembedded/bitbake.git
git clone git://github.com/kraj/meta-clang.git

$ . ./oe-init-build-env

Add meta-clang overlay

bitbake-layers add-layer ../meta-clang

Check conf/bblayers.conf to see that meta-clang is added to layer mix e.g.

Default Compiler Switch

Note that by default gcc will remain the system compiler, however if you wish clang to be the default compiler then set

TOOLCHAIN ?= "clang"

in local.conf, this would now switch default cross-compiler to be clang you can select clang per recipe too by writing bbappends for them containing

TOOLCHAIN = "clang"

Default C++ Standard Library Switch

Note that by default clang libc++ is default C++ standard library, however if you wish to keep GNU libstdc++ to be the default then set

LIBCPLUSPLUS = ""

in local.conf. You can select libstdc++ per package too by writing bbappends for them containing

LIBCPLUSPLUS_toolchain-clang_pn-<recipe> = ""

Default Compiler Runtime ( Compiler-rt + libc++ )

By default, clang build from meta-clang uses clang runtime ( compiler-rt + libc++ + libunwind ) out of box However, it is possible to switch to using gcc runtime as default, In order to do that following settings are needed in site configurations e.g. in local.conf

TOOLCHAIN ?= "clang"
LIBCPLUSPLUS = ""
COMPILER_RT = ""
UNWINDLIB = ""

Removing clang from generated SDK toolchain

clang based cross compiler is automatically included into the generated SDK using bitbake meta-toolchain or bitbake -cpopulate_sdk <image> in circumstanced where clang is not expected to be part of SDK, then reset CLANGSDK variable in local.conf

CLANGSDK = ""

Building

Below we build for qemuarm machine as an example

$ MACHINE=qemuarm bitbake core-image-full-cmdline

Running

$ runqemu nographic

Limitations

Few components do not build with clang, if you have a component to add to that list simply add it to conf/nonclangable.inc e.g.

TOOLCHAIN_pn-<recipe> = "gcc"

and OE will start using gcc to cross compile that recipe.

And if a component does not build with libc++, you can add it to conf/nonclangable.inc e.g.

CXX_remove_pn-<recipe>_toolchain-clang = " -stdlib=libc++ "

Dependencies

URI: git://github.com/openembedded/openembedded-core.git
branch: master
revision: HEAD

URI: git://github.com/openembedded/bitbake.git
branch: master
revision: HEAD

Contributing

You are encouraged to follow Github Pull request workflow to share changes and following commit message guidelines are recommended OE patch guidelines

Layer Maintainer: Khem Raj