I’m very glad that I’m accepted by Gentoo as a participant of Google Summer of Code this year. During this summer, I’ll be working on building a clang-based toolchain for Gentoo.
Clang is a modern C/C++ compiler developed by LLVM, famous for its modular design and non-intrusive license. The ideal result of this project is to provide a Gentoo profile, where clang is the default compiler in place of gcc.
As clang is written in C++, it needs a C++ runtime to work, which are basically a C standard library, a C++ standard library, a C++ ABI library and a stack unwinder. On a typical Linux host, glibc and libstdc++ are the de facto C and C++ standard libraries respectively. The functionality of C++ ABI library is also integrated in libstdc++; the stack unwinder is implemented in libgcc.
libstdc++ and libgcc are both parts of GCC, which won’t be available when we deploy clang as the default compiler. Luckily, besides clang, LLVM also developed a complete implementation of the C++ runtime, consisting of three libraries: libc++, libc++abi and libunwind. Unlike GCC, the C++ ABI library is implemented separately. To decouple our toolchain further from the GNU toolset, we’ll use musl as the libc.
Sum it up
In this project, we’ll build a toolchain with clang as the compiler, musl as libc and a C++ runtime composed of libc++, libc++abi and libunwind. If everything goes smoothly, this setup will be offered as a Gentoo profile; users who like the neat features of clang thus have the chance to say goodbye to GCC 
I’ll update this blog regularly to reflect my most recent progress and share technical stuff that might be helpful to others. Stay tuned !