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Installing LLVMs libcxx on linux

libcxx on linux

Currently Clang is shipped using GNUs STL by default, which is basically a C++98 library with some C++11 features added. libc++ is LLVMs C++11 implementation of the C++ Standard Library, which is written for C++11 and thus might provide some benefits for C++11 code. Also there are some license concerns with GNUs STL, however, as of today, you don't really get rid of GNU dependencies it if you use Clang on linux.

While Clang support for libc++ and the library itself is envoling, you still need to compile libc++ and libc++abi on your own. At least i don't know about any distributions which package Clang with libc++ included.


Installing libc++ is easy. For this article, i ignore packaging as well as any distro-specific concerns, you should easily be able to adjust the steps to your distribution. You need to install Clang first and need to know where Clangs prefix is, i assume /usr

export BASEDIR="$PWD"
svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx
cd libcxx/lib
sudo cp libc++.so.1.0 /usr/lib/
sudo cp -R ../include /usr/include/c++/v1
sudo ln -s libc++.so.1.0 /usr/lib/libc++.so
sudo ldconfig


libc++abi apperas to be not very well tested on linux, the primary developmentplatform is Mac OS-X. To compile it, you'll need to copy gccs internal unwind.h, that will be found in the libdir of gcc. Also i needed to replace __unwind_word__ with __word__, which might or might not be identically on your platform

svn co http://llvm.org/svn/llvm-project/libcxxabi/trunk libcxxabi
cd libcxxabi/include
sed 's/__unwind_word__/__word__/g' /usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.1/include/unwind.h > unwind.h
cd ../lib
sudo cp libcxxabi/lib/libc++abi.so.1.0 /usr/lib
sudo ln -s libc++abi.so.1.0 /usr/lib/libc++abi.so
sudo ldconfig


Now you can use libc++ it if you add the right paramenters to clang++

clang++ -std=c++11 -stdlib=libc++ -lc++abi -o test test.cpp

Unfortunately the implementation is still incomplete. However, it might be complete enough for you to play arround with some features. If you run the test, you'll see what is working.

cd $BASEDIR/libcxx/test
export OPTIONS="-std=c++11 -stdlib=libc++ -lc++abi"

Most tests are passing allready, however, there are some important features that are not working and of course, there is no evidence, that the tests cover the full featureset of C++11.

Results for libcxx/test:
using clang version 3.1 (branches/release_31)
Target: x86_64-unknown-linux-gnu
Thread model: posix
with -std=c++11 -stdlib=libc++ -lc++abi  
sections without tests   : 0
sections with failures   : 51
sections without failures: 1013
                       +   ----
total number of sections : 1064
number of tests failed   : 186
number of tests passed   : 4153
                       +   ----
total number of tests    : 4339
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