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 or Yocto Project 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
If using poky ( Yocto project reference Distribution )
git clone https://git.yoctoproject.org/git/poky
cd poky
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