libc++ is the C++ standard library implemented by LLVM and an essential part of the clang-based\u00a0toolchain we’re going to build. In this post I’ll demonstrate\u00a0how to build a freestanding libc++ on Gentoo.<\/p>\n
A complete C++ runtime stack consists of three components, from top to bottom:<\/p>\n
As stated in my introductory\u00a0post, in this GSoC project these roles will be taken by libc++, libc++abi and libunwind, respectively. As higher-level libraries depend on lower-level ones, we need to build them from bottom to top, i.e. :<\/p>\n
All of the above, of course, should\u00a0be linked with musl instead of glibc. So first of all, we need a proper toolchain that can link binaries with musl. Luckily, Gentoo’s developers already prepared such a toolchain for us; just type the following commands: Here we use Build libunwind:<\/strong> Note: I want to statically link libunwind into libc++abi, so I disable the building of\u00a0shared library through Build libc++abi:<\/strong> Build libc++:<\/strong> Note: libgcc is GCC’s stack unwinding library and should\u00a0not be used in our C++ runtime stack, so I explicitly disable it through Now the C++ runtime stack is complete; it’s time to verify our work: libunwind is statically linked so is not shown. Dependencies on libc++abi and libc (musl) look correct. So far, so good \ud83d\ude42<\/p>\n In the following post, I’ll demonstrate how to link an actual C++ program with this freshly built libc++.\u00a0See you!<\/p>\n","protected":false},"excerpt":{"rendered":" libc++ is the C++ standard library implemented by LLVM and an essential part of the clang-based\u00a0toolchain we’re going to build. In this post I’ll demonstrate\u00a0how to build a freestanding libc++ on Gentoo. A complete C++ runtime stack consists of three components, from top to bottom: a C++ standard library a C++ ABI library a stack … Continue reading Build a freestanding libc++<\/span><\/a><\/p>\n","protected":false},"author":161,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[2],"tags":[],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/posts\/11"}],"collection":[{"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/users\/161"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/comments?post=11"}],"version-history":[{"count":13,"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/posts\/11\/revisions"}],"predecessor-version":[{"id":46,"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/posts\/11\/revisions\/46"}],"wp:attachment":[{"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/media?parent=11"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/categories?post=11"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.gentoo.org\/gsoc2016-native-clang\/wp-json\/wp\/v2\/tags?post=11"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\n
\n$ emerge layman crossdev && layman -a musl && \\
\ncrossdev -t x86_64-pc-linux-musl
\n<\/code><\/p>\nlayman<\/code> to create a layout\u00a0for musl, and then use crossdev<\/code> to auto-magically build the toolchain. Check out all needed respositories and we are ready to build the libraries:
\n<\/code><\/p>\n$ cd $REPOS
\n$ svn co http:\/\/llvm.org\/svn\/llvm-project\/llvm\/trunk llvm
\n$ svn co http:\/\/llvm.org\/svn\/llvm-project\/libunwind\/trunk libunwind
\n$ svn co http:\/\/llvm.org\/svn\/llvm-project\/libcxxabi\/trunk libcxxabi
\n$ svn co http:\/\/llvm.org\/svn\/llvm-project\/libcxx\/trunk libcxx
\n<\/code><\/p>\n
\n
\n$ cd $REPOS\/libunwind && mkdir build && cd build
\n$ cmake -DCMAKE_C_COMPILER=x86_64-pc-linux-musl-gcc \\
\n-DCMAKE_CXX_COMPILER=x86_64-pc-linux-musl-g++ \\
\n-DLIBUNWIND_ENABLE_SHARED=0 \\
\n-DLLVM_PATH=\"$REPOS\/llvm\" ..
\n$ make
\n<\/code><\/p>\nLIBUNWIND_ENABLE_SHARED<\/code>. You may safely omit this option if you want a shared version.<\/p>\n
\n
\n$ cd $REPOS\/libc++abi && mkdir build && cd build
\n$ cmake -DCMAKE_C_COMPILER=x86_64-pc-linux-musl-gcc \\
\n-DCMAKE_CXX_COMPILER=x86_64-pc-linux-musl-g++ \\
\n-DCMAKE_SHARED_LINKER_FLAGS=\"-L$REPOS\/libunwind\/build\/lib\"
\n-DLIBCXXABI_USE_LLVM_UNWINDER=1 \\
\n-DLIBCXXABI_LIBUNWIND_PATH=\"$REPOS\/libunwind\" \\
\n-DLIBCXXABI_LIBCXX_INCLUDES=\"$REPOS\/libcxx\/include\" \\
\n-DLLVM_PATH=\"$REPOS\/llvm\" ..
\n$ make
\n<\/code><\/p>\n
\n
\n$ cd $REPOS\/libc++ && mkdir build && cd build
\n$ cmake -DCMAKE_C_COMPILER=x86_64-pc-linux-musl-gcc \\
\n-DCMAKE_CXX_COMPILER=x86_64-pc-linux-musl-g++ \\
\n-DLIBCXX_HAS_MUSL_LIBC=1 \\
\n-DLIBCXX_HAS_GCC_S_LIB=0 \\
\n-DLIBCXX_CXX_ABI=libcxxabi \\
\n-DLIBCXX_CXX_ABI_INCLUDE_PATHS=\"$REPOS\/libcxxabi\/include\" \\
\n-DLIBCXX_CXX_ABI_LIBRARY_PATH=\"$REPOS\/libcxxabi\/build\/lib\" \\
\n-DLLVM_PATH=\"$REPOS\/llvm\" \\
\n$ make
\n<\/code><\/p>\nLIBCXX_HAS_GCC_S_LIB<\/code>\u00a0; otherwise it’ll sneak into our library.<\/p>\n
\n
\n$ readelf -d $REPOS\/libcxx\/build\/lib\/libc++.so.1 | grep NEEDED
\n0x0000000000000001 (NEEDED) Shared library: [libc++abi.so.1]
\n0x0000000000000001 (NEEDED) Shared library: [libc.so]
\n<\/code><\/p>\n