docs/BuildingLibcxx.rst - libcxx - Git at Google

 .. _BuildingLibcxx:

 ===============
 Building libc++
 ===============

 .. contents::
   :local:

 .. _build instructions:

 Getting Started
 ===============

 On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install
 Xcode 4.2 or later.  However if you want to install tip-of-trunk from here
 (getting the bleeding edge), read on.

 The basic steps needed to build libc++ are:

 #. Checkout and configure LLVM (including libc++ and libc++abi), according to the `LLVM
    getting started <https://llvm.org/docs/GettingStarted.html>`_ documentation. Make sure
    to include ``libcxx`` and ``libcxxabi`` in the ``LLVM_ENABLE_PROJECTS`` option passed
    to CMake.

    For more information about configuring libc++ see :ref:`CMake Options`.

    * ``make cxx`` --- will build libc++ and libc++abi.
    * ``make check-cxx check-cxxabi`` --- will run the test suites.

    Shared libraries for libc++ and libc++ abi should now be present in llvm/build/lib.
    See :ref:`using an alternate libc++ installation <alternate libcxx>`

 #. **Optional**: Install libc++ and libc++abi

    If your system already provides a libc++ installation it is important to be
    careful not to replace it. Remember Use the CMake option ``CMAKE_INSTALL_PREFIX`` to
    select a safe place to install libc++.

    * ``make install-cxx install-cxxabi`` --- Will install the libraries and the headers

    .. warning::
      * Replacing your systems libc++ installation could render the system non-functional.
      * macOS will not boot without a valid copy of ``libc++.1.dylib`` in ``/usr/lib``.


 The instructions are for building libc++ on
 FreeBSD, Linux, or Mac using `libc++abi`_ as the C++ ABI library.
 On Linux, it is also possible to use :ref:`libsupc++ <libsupcxx>` or libcxxrt.

 It is sometimes beneficial to build separately from the full LLVM build. An
 out-of-tree build would look like this:

 .. code-block:: bash

   $ cd where-you-want-libcxx-to-live
   $ # Check out the sources (includes everything, but we'll only use libcxx)
   $ ``git clone https://github.com/llvm/llvm-project.git``
   $ cd where-you-want-to-build
   $ mkdir build && cd build
   $ export CC=clang CXX=clang++
   $ cmake -DLLVM_PATH=path/to/separate/llvm \
           -DLIBCXX_CXX_ABI=libcxxabi \
           -DLIBCXX_CXX_ABI_INCLUDE_PATHS=path/to/separate/libcxxabi/include \
           path/to/llvm-project/libcxx
   $ make
   $ make check-libcxx # optional


 Experimental Support for Windows
 --------------------------------

 The Windows support requires building with clang-cl as cl does not support one
 required extension: `#include_next`.  Furthermore, VS 2015 or newer (19.00) is
 required.  In the case of clang-cl, we need to specify the "MS Compatibility
 Version" as it defaults to 2014 (18.00).

 CMake + Visual Studio
 ~~~~~~~~~~~~~~~~~~~~~

 Building with Visual Studio currently does not permit running tests. However,
 it is the simplest way to build.

 .. code-block:: batch

   > cmake -G "Visual Studio 14 2015"              ^
           -T "LLVM-vs2014"                        ^
           -DLIBCXX_ENABLE_SHARED=YES              ^
           -DLIBCXX_ENABLE_STATIC=NO               ^
           -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=NO ^
           \path\to\libcxx
   > cmake --build .

 CMake + ninja
 ~~~~~~~~~~~~~

 Building with ninja is required for development to enable tests.
 Unfortunately, doing so requires additional configuration as we cannot
 just specify a toolset.

 .. code-block:: batch

   > cmake -G Ninja                                                                    ^
           -DCMAKE_MAKE_PROGRAM=/path/to/ninja                                         ^
           -DCMAKE_SYSTEM_NAME=Windows                                                 ^
           -DCMAKE_C_COMPILER=clang-cl                                                 ^
           -DCMAKE_C_FLAGS="-fms-compatibility-version=19.00 --target=i686--windows"   ^
           -DCMAKE_CXX_COMPILER=clang-cl                                                ^
           -DCMAKE_CXX_FLAGS="-fms-compatibility-version=19.00 --target=i686--windows" ^
           -DLLVM_PATH=/path/to/llvm/tree                                              ^
           -DLIBCXX_ENABLE_SHARED=YES                                                  ^
           -DLIBCXX_ENABLE_STATIC=NO                                                   ^
           -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=NO                                     ^
           \path\to\libcxx
   > /path/to/ninja cxx
   > /path/to/ninja check-cxx

 Note that the paths specified with backward slashes must use the `\\` as the
 directory separator as clang-cl may otherwise parse the path as an argument.

 .. _`libc++abi`: http://libcxxabi.llvm.org/


 .. _CMake Options:

 CMake Options
 =============

 Here are some of the CMake variables that are used often, along with a
 brief explanation and LLVM-specific notes. For full documentation, check the
 CMake docs or execute ``cmake --help-variable VARIABLE_NAME``.

 **CMAKE_BUILD_TYPE**:STRING
   Sets the build type for ``make`` based generators. Possible values are
   Release, Debug, RelWithDebInfo and MinSizeRel. On systems like Visual Studio
   the user sets the build type with the IDE settings.

 **CMAKE_INSTALL_PREFIX**:PATH
   Path where LLVM will be installed if "make install" is invoked or the
   "INSTALL" target is built.

 **CMAKE_CXX_COMPILER**:STRING
   The C++ compiler to use when building and testing libc++.


 .. _libcxx-specific options:

 libc++ specific options
 -----------------------

 .. option:: LIBCXX_INSTALL_LIBRARY:BOOL

   **Default**: ``ON``

   Toggle the installation of the library portion of libc++.

 .. option:: LIBCXX_INSTALL_HEADERS:BOOL

   **Default**: ``ON``

   Toggle the installation of the libc++ headers.

 .. option:: LIBCXX_ENABLE_ASSERTIONS:BOOL

   **Default**: ``ON``

   Build libc++ with assertions enabled.

 .. option:: LIBCXX_BUILD_32_BITS:BOOL

   **Default**: ``OFF``

   Build libc++ as a 32 bit library. Also see `LLVM_BUILD_32_BITS`.

 .. option:: LIBCXX_ENABLE_SHARED:BOOL

   **Default**: ``ON``

   Build libc++ as a shared library. Either `LIBCXX_ENABLE_SHARED` or
   `LIBCXX_ENABLE_STATIC` has to be enabled.

 .. option:: LIBCXX_ENABLE_STATIC:BOOL

   **Default**: ``ON``

   Build libc++ as a static library. Either `LIBCXX_ENABLE_SHARED` or
   `LIBCXX_ENABLE_STATIC` has to be enabled.

 .. option:: LIBCXX_LIBDIR_SUFFIX:STRING

   Extra suffix to append to the directory where libraries are to be installed.
   This option overrides `LLVM_LIBDIR_SUFFIX`.

 .. option:: LIBCXX_INSTALL_PREFIX:STRING

   **Default**: ``""``

   Define libc++ destination prefix.

 .. option:: LIBCXX_HERMETIC_STATIC_LIBRARY:BOOL

   **Default**: ``OFF``

   Do not export any symbols from the static libc++ library.
   This is useful when the static libc++ library is being linked into shared
   libraries that may be used in with other shared libraries that use different
   C++ library. We want to avoid avoid exporting any libc++ symbols in that case.

 .. option:: LIBCXX_ENABLE_FILESYSTEM:BOOL

    **Default**: ``ON`` except on Windows.

    This option can be used to enable or disable the filesystem components on
    platforms that may not support them. For example on Windows.

 .. _libc++experimental options:

 libc++experimental Specific Options
 ------------------------------------

 .. option:: LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY:BOOL

   **Default**: ``ON``

   Build and test libc++experimental.a.

 .. option:: LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY:BOOL

   **Default**: ``LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY AND LIBCXX_INSTALL_LIBRARY``

   Install libc++experimental.a alongside libc++.


 .. _ABI Library Specific Options:

 ABI Library Specific Options
 ----------------------------

 .. option:: LIBCXX_CXX_ABI:STRING

   **Values**: ``none``, ``libcxxabi``, ``libcxxrt``, ``libstdc++``, ``libsupc++``.

   Select the ABI library to build libc++ against.

 .. option:: LIBCXX_CXX_ABI_INCLUDE_PATHS:PATHS

   Provide additional search paths for the ABI library headers.

 .. option:: LIBCXX_CXX_ABI_LIBRARY_PATH:PATH

   Provide the path to the ABI library that libc++ should link against.

 .. option:: LIBCXX_ENABLE_STATIC_ABI_LIBRARY:BOOL

   **Default**: ``OFF``

   If this option is enabled, libc++ will try and link the selected ABI library
   statically.

 .. option:: LIBCXX_ENABLE_ABI_LINKER_SCRIPT:BOOL

   **Default**: ``ON`` by default on UNIX platforms other than Apple unless
   'LIBCXX_ENABLE_STATIC_ABI_LIBRARY' is ON. Otherwise the default value is ``OFF``.

   This option generate and installs a linker script as ``libc++.so`` which
   links the correct ABI library.

 .. option:: LIBCXXABI_USE_LLVM_UNWINDER:BOOL

   **Default**: ``OFF``

   Build and use the LLVM unwinder. Note: This option can only be used when
   libc++abi is the C++ ABI library used.


 libc++ Feature Options
 ----------------------

 .. option:: LIBCXX_ENABLE_EXCEPTIONS:BOOL

   **Default**: ``ON``

   Build libc++ with exception support.

 .. option:: LIBCXX_ENABLE_RTTI:BOOL

   **Default**: ``ON``

   Build libc++ with run time type information.

 .. option:: LIBCXX_INCLUDE_BENCHMARKS:BOOL

   **Default**: ``ON``

   Build the libc++ benchmark tests and the Google Benchmark library needed
   to support them.

 .. option:: LIBCXX_BENCHMARK_TEST_ARGS:STRING

   **Default**: ``--benchmark_min_time=0.01``

   A semicolon list of arguments to pass when running the libc++ benchmarks using the
   ``check-cxx-benchmarks`` rule. By default we run the benchmarks for a very short amount of time,
   since the primary use of ``check-cxx-benchmarks`` is to get test and sanitizer coverage, not to
   get accurate measurements.

 .. option:: LIBCXX_BENCHMARK_NATIVE_STDLIB:STRING

   **Default**:: ``""``

   **Values**:: ``libc++``, ``libstdc++``

   Build the libc++ benchmark tests and Google Benchmark library against the
   specified standard library on the platform. On linux this can be used to
   compare libc++ to libstdc++ by building the benchmark tests against both
   standard libraries.

 .. option:: LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN:STRING

   Use the specified GCC toolchain and standard library when building the native
   stdlib benchmark tests.

 .. option:: LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT:BOOL

   **Default**: ``OFF``

   Pick the default for whether to constrain ABI-unstable symbols to
   each individual translation unit. This setting controls whether
   `_LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT` is defined by default --
   see the documentation of that macro for details.


 libc++ ABI Feature Options
 --------------------------

 The following options allow building libc++ for a different ABI version.

 .. option:: LIBCXX_ABI_VERSION:STRING

   **Default**: ``1``

   Defines the target ABI version of libc++.

 .. option:: LIBCXX_ABI_UNSTABLE:BOOL

   **Default**: ``OFF``

   Build the "unstable" ABI version of libc++. Includes all ABI changing features
   on top of the current stable version.

 .. option:: LIBCXX_ABI_NAMESPACE:STRING

   **Default**: ``__n`` where ``n`` is the current ABI version.

   This option defines the name of the inline ABI versioning namespace. It can be used for building
   custom versions of libc++ with unique symbol names in order to prevent conflicts or ODR issues
   with other libc++ versions.

   .. warning::
     When providing a custom namespace, it's the users responsibility to ensure the name won't cause
     conflicts with other names defined by libc++, both now and in the future. In particular, inline
     namespaces of the form ``__[0-9]+`` are strictly reserved by libc++ and may not be used by users.
     Doing otherwise could cause conflicts and hinder libc++ ABI evolution.

 .. option:: LIBCXX_ABI_DEFINES:STRING

   **Default**: ``""``

   A semicolon-separated list of ABI macros to persist in the site config header.
   See ``include/__config`` for the list of ABI macros.


 .. option:: LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT

   **Default**: ``None``. When defined this option overrides the libraries default configuration
   for whether merged type info names are present.


   Build ``std::type_info`` with the assumption that type info names for a type have been fully
   merged are unique across the entire program. This may not be the case for libraries built with
   ``-Bsymbolic`` or due to compiler or linker bugs (Ex. llvm.org/PR37398).

   When the value is ``ON`` typeinfo comparisons compare only the pointer value, otherwise ``strcmp``
   is used as a fallback.


 .. _LLVM-specific variables:

 LLVM-specific options
 ---------------------

 .. option:: LLVM_LIBDIR_SUFFIX:STRING

   Extra suffix to append to the directory where libraries are to be
   installed. On a 64-bit architecture, one could use ``-DLLVM_LIBDIR_SUFFIX=64``
   to install libraries to ``/usr/lib64``.

 .. option:: LLVM_BUILD_32_BITS:BOOL

   Build 32-bits executables and libraries on 64-bits systems. This option is
   available only on some 64-bits unix systems. Defaults to OFF.

 .. option:: LLVM_LIT_ARGS:STRING

   Arguments given to lit.  ``make check`` and ``make clang-test`` are affected.
   By default, ``'-sv --no-progress-bar'`` on Visual C++ and Xcode, ``'-sv'`` on
   others.


 Using Alternate ABI libraries
 =============================


 .. _libsupcxx:

 Using libsupc++ on Linux
 ------------------------

 You will need libstdc++ in order to provide libsupc++.

 Figure out where the libsupc++ headers are on your system. On Ubuntu this
 is ``/usr/include/c++/<version>`` and ``/usr/include/c++/<version>/<target-triple>``

 You can also figure this out by running

 .. code-block:: bash

   $ echo | g++ -Wp,-v -x c++ - -fsyntax-only
   ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
   ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
   #include "..." search starts here:
   #include &lt;...&gt; search starts here:
   /usr/include/c++/4.7
   /usr/include/c++/4.7/x86_64-linux-gnu
   /usr/include/c++/4.7/backward
   /usr/lib/gcc/x86_64-linux-gnu/4.7/include
   /usr/local/include
   /usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
   /usr/include/x86_64-linux-gnu
   /usr/include
   End of search list.

 Note that the first two entries happen to be what we are looking for. This
 may not be correct on other platforms.

 We can now run CMake:

 .. code-block:: bash

   $ CC=clang CXX=clang++ cmake -G "Unix Makefiles" \
     -DLIBCXX_CXX_ABI=libstdc++ \
     -DLIBCXX_CXX_ABI_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/" \
     -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr \
     <libc++-source-dir>


 You can also substitute ``-DLIBCXX_CXX_ABI=libsupc++``
 above, which will cause the library to be linked to libsupc++ instead
 of libstdc++, but this is only recommended if you know that you will
 never need to link against libstdc++ in the same executable as libc++.
 GCC ships libsupc++ separately but only as a static library.  If a
 program also needs to link against libstdc++, it will provide its
 own copy of libsupc++ and this can lead to subtle problems.

 .. code-block:: bash

   $ make cxx
   $ make install

 You can now run clang with -stdlib=libc++.


 .. _libcxxrt_ref:

 Using libcxxrt on Linux
 ------------------------

 You will need to keep the source tree of `libcxxrt`_ available
 on your build machine and your copy of the libcxxrt shared library must
 be placed where your linker will find it.

 We can now run CMake like:

 .. code-block:: bash

   $ CC=clang CXX=clang++ cmake -G "Unix Makefiles" \
           -DLIBCXX_CXX_ABI=libcxxrt \
           -DLIBCXX_CXX_ABI_INCLUDE_PATHS=path/to/libcxxrt-sources/src \
                 -DCMAKE_BUILD_TYPE=Release \
                 -DCMAKE_INSTALL_PREFIX=/usr \
                 <libc++-source-directory>
   $ make cxx
   $ make install

 Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
 clang is set up to link for libc++ linked to libsupc++.  To get around this
 you'll have to set up your linker yourself (or patch clang).  For example,

 .. code-block:: bash

   $ clang++ -stdlib=libc++ helloworld.cpp \
             -nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc

 Alternately, you could just add libcxxrt to your libraries list, which in most
 situations will give the same result:

 .. code-block:: bash

   $ clang++ -stdlib=libc++ helloworld.cpp -lcxxrt

 .. _`libcxxrt`: https://github.com/pathscale/libcxxrt/


 Using a local ABI library installation
 ---------------------------------------

 .. warning::
   This is not recommended in almost all cases.

 These instructions should only be used when you can't install your ABI library.

 Normally you must link libc++ against a ABI shared library that the
 linker can find.  If you want to build and test libc++ against an ABI
 library not in the linker's path you needq to set
 ``-DLIBCXX_CXX_ABI_LIBRARY_PATH=/path/to/abi/lib`` when configuring CMake.

 An example build using libc++abi would look like:

 .. code-block:: bash

   $ CC=clang CXX=clang++ cmake \
               -DLIBCXX_CXX_ABI=libc++abi  \
               -DLIBCXX_CXX_ABI_INCLUDE_PATHS="/path/to/libcxxabi/include" \
               -DLIBCXX_CXX_ABI_LIBRARY_PATH="/path/to/libcxxabi-build/lib" \
                path/to/libcxx
   $ make

 When testing libc++ LIT will automatically link against the proper ABI
 library.
	.. _BuildingLibcxx:

	===============
	Building libc++
	===============

	.. contents::
	:local:

	.. _build instructions:

	Getting Started
	===============

	On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install
	Xcode 4.2 or later. However if you want to install tip-of-trunk from here
	(getting the bleeding edge), read on.

	The basic steps needed to build libc++ are:

	#. Checkout and configure LLVM (including libc++ and libc++abi), according to the `LLVM
	getting started <https://llvm.org/docs/GettingStarted.html>`_ documentation. Make sure
	to include ``libcxx`` and ``libcxxabi`` in the ``LLVM_ENABLE_PROJECTS`` option passed
	to CMake.

	For more information about configuring libc++ see :ref:`CMake Options`.

	* ``make cxx`` --- will build libc++ and libc++abi.
	* ``make check-cxx check-cxxabi`` --- will run the test suites.

	Shared libraries for libc++ and libc++ abi should now be present in llvm/build/lib.
	See :ref:`using an alternate libc++ installation <alternate libcxx>`

	#. Optional: Install libc++ and libc++abi

	If your system already provides a libc++ installation it is important to be
	careful not to replace it. Remember Use the CMake option ``CMAKE_INSTALL_PREFIX`` to
	select a safe place to install libc++.

	* ``make install-cxx install-cxxabi`` --- Will install the libraries and the headers

	.. warning::
	* Replacing your systems libc++ installation could render the system non-functional.
	* macOS will not boot without a valid copy of ``libc++.1.dylib`` in ``/usr/lib``.


	The instructions are for building libc++ on
	FreeBSD, Linux, or Mac using `libc++abi`_ as the C++ ABI library.
	On Linux, it is also possible to use :ref:`libsupc++ <libsupcxx>` or libcxxrt.

	It is sometimes beneficial to build separately from the full LLVM build. An
	out-of-tree build would look like this:

	.. code-block:: bash

	$ cd where-you-want-libcxx-to-live
	$ # Check out the sources (includes everything, but we'll only use libcxx)
	$ ``git clone https://github.com/llvm/llvm-project.git``
	$ cd where-you-want-to-build
	$ mkdir build && cd build
	$ export CC=clang CXX=clang++
	$ cmake -DLLVM_PATH=path/to/separate/llvm \
	-DLIBCXX_CXX_ABI=libcxxabi \
	-DLIBCXX_CXX_ABI_INCLUDE_PATHS=path/to/separate/libcxxabi/include \
	path/to/llvm-project/libcxx
	$ make
	$ make check-libcxx # optional


	Experimental Support for Windows
	--------------------------------

	The Windows support requires building with clang-cl as cl does not support one
	required extension: `#include_next`. Furthermore, VS 2015 or newer (19.00) is
	required. In the case of clang-cl, we need to specify the "MS Compatibility
	Version" as it defaults to 2014 (18.00).

	CMake + Visual Studio
	~~~~~~~~~~~~~~~~~~~~~

	Building with Visual Studio currently does not permit running tests. However,
	it is the simplest way to build.

	.. code-block:: batch

	> cmake -G "Visual Studio 14 2015" ^
	-T "LLVM-vs2014" ^
	-DLIBCXX_ENABLE_SHARED=YES ^
	-DLIBCXX_ENABLE_STATIC=NO ^
	-DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=NO ^
	\path\to\libcxx
	> cmake --build .

	CMake + ninja
	~~~~~~~~~~~~~

	Building with ninja is required for development to enable tests.
	Unfortunately, doing so requires additional configuration as we cannot
	just specify a toolset.

	.. code-block:: batch

	> cmake -G Ninja ^
	-DCMAKE_MAKE_PROGRAM=/path/to/ninja ^
	-DCMAKE_SYSTEM_NAME=Windows ^
	-DCMAKE_C_COMPILER=clang-cl ^
	-DCMAKE_C_FLAGS="-fms-compatibility-version=19.00 --target=i686--windows" ^
	-DCMAKE_CXX_COMPILER=clang-cl ^
	-DCMAKE_CXX_FLAGS="-fms-compatibility-version=19.00 --target=i686--windows" ^
	-DLLVM_PATH=/path/to/llvm/tree ^
	-DLIBCXX_ENABLE_SHARED=YES ^
	-DLIBCXX_ENABLE_STATIC=NO ^
	-DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=NO ^
	\path\to\libcxx
	> /path/to/ninja cxx
	> /path/to/ninja check-cxx

	Note that the paths specified with backward slashes must use the `\\` as the
	directory separator as clang-cl may otherwise parse the path as an argument.

	.. _`libc++abi`: http://libcxxabi.llvm.org/


	.. _CMake Options:

	CMake Options
	=============

	Here are some of the CMake variables that are used often, along with a
	brief explanation and LLVM-specific notes. For full documentation, check the
	CMake docs or execute ``cmake --help-variable VARIABLE_NAME``.

	CMAKE_BUILD_TYPE:STRING
	Sets the build type for ``make`` based generators. Possible values are
	Release, Debug, RelWithDebInfo and MinSizeRel. On systems like Visual Studio
	the user sets the build type with the IDE settings.

	CMAKE_INSTALL_PREFIX:PATH
	Path where LLVM will be installed if "make install" is invoked or the
	"INSTALL" target is built.

	CMAKE_CXX_COMPILER:STRING
	The C++ compiler to use when building and testing libc++.


	.. _libcxx-specific options:

	libc++ specific options
	-----------------------

	.. option:: LIBCXX_INSTALL_LIBRARY:BOOL

	Default: ``ON``

	Toggle the installation of the library portion of libc++.

	.. option:: LIBCXX_INSTALL_HEADERS:BOOL

	Default: ``ON``

	Toggle the installation of the libc++ headers.

	.. option:: LIBCXX_ENABLE_ASSERTIONS:BOOL

	Default: ``ON``

	Build libc++ with assertions enabled.

	.. option:: LIBCXX_BUILD_32_BITS:BOOL

	Default: ``OFF``

	Build libc++ as a 32 bit library. Also see `LLVM_BUILD_32_BITS`.

	.. option:: LIBCXX_ENABLE_SHARED:BOOL

	Default: ``ON``

	Build libc++ as a shared library. Either `LIBCXX_ENABLE_SHARED` or
	`LIBCXX_ENABLE_STATIC` has to be enabled.

	.. option:: LIBCXX_ENABLE_STATIC:BOOL

	Default: ``ON``

	Build libc++ as a static library. Either `LIBCXX_ENABLE_SHARED` or
	`LIBCXX_ENABLE_STATIC` has to be enabled.

	.. option:: LIBCXX_LIBDIR_SUFFIX:STRING

	Extra suffix to append to the directory where libraries are to be installed.
	This option overrides `LLVM_LIBDIR_SUFFIX`.

	.. option:: LIBCXX_INSTALL_PREFIX:STRING

	Default: ``""``

	Define libc++ destination prefix.

	.. option:: LIBCXX_HERMETIC_STATIC_LIBRARY:BOOL

	Default: ``OFF``

	Do not export any symbols from the static libc++ library.
	This is useful when the static libc++ library is being linked into shared
	libraries that may be used in with other shared libraries that use different
	C++ library. We want to avoid avoid exporting any libc++ symbols in that case.

	.. option:: LIBCXX_ENABLE_FILESYSTEM:BOOL

	Default: ``ON`` except on Windows.

	This option can be used to enable or disable the filesystem components on
	platforms that may not support them. For example on Windows.

	.. _libc++experimental options:

	libc++experimental Specific Options
	------------------------------------

	.. option:: LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY:BOOL

	Default: ``ON``

	Build and test libc++experimental.a.

	.. option:: LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY:BOOL

	Default: ``LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY AND LIBCXX_INSTALL_LIBRARY``

	Install libc++experimental.a alongside libc++.


	.. _ABI Library Specific Options:

	ABI Library Specific Options
	----------------------------

	.. option:: LIBCXX_CXX_ABI:STRING

	Values: ``none``, ``libcxxabi``, ``libcxxrt``, ``libstdc++``, ``libsupc++``.

	Select the ABI library to build libc++ against.

	.. option:: LIBCXX_CXX_ABI_INCLUDE_PATHS:PATHS

	Provide additional search paths for the ABI library headers.

	.. option:: LIBCXX_CXX_ABI_LIBRARY_PATH:PATH

	Provide the path to the ABI library that libc++ should link against.

	.. option:: LIBCXX_ENABLE_STATIC_ABI_LIBRARY:BOOL

	Default: ``OFF``

	If this option is enabled, libc++ will try and link the selected ABI library
	statically.

	.. option:: LIBCXX_ENABLE_ABI_LINKER_SCRIPT:BOOL

	Default: ``ON`` by default on UNIX platforms other than Apple unless
	'LIBCXX_ENABLE_STATIC_ABI_LIBRARY' is ON. Otherwise the default value is ``OFF``.

	This option generate and installs a linker script as ``libc++.so`` which
	links the correct ABI library.

	.. option:: LIBCXXABI_USE_LLVM_UNWINDER:BOOL

	Default: ``OFF``

	Build and use the LLVM unwinder. Note: This option can only be used when
	libc++abi is the C++ ABI library used.


	libc++ Feature Options
	----------------------

	.. option:: LIBCXX_ENABLE_EXCEPTIONS:BOOL

	Default: ``ON``

	Build libc++ with exception support.

	.. option:: LIBCXX_ENABLE_RTTI:BOOL

	Default: ``ON``

	Build libc++ with run time type information.

	.. option:: LIBCXX_INCLUDE_BENCHMARKS:BOOL

	Default: ``ON``

	Build the libc++ benchmark tests and the Google Benchmark library needed
	to support them.

	.. option:: LIBCXX_BENCHMARK_TEST_ARGS:STRING

	Default: ``--benchmark_min_time=0.01``

	A semicolon list of arguments to pass when running the libc++ benchmarks using the
	``check-cxx-benchmarks`` rule. By default we run the benchmarks for a very short amount of time,
	since the primary use of ``check-cxx-benchmarks`` is to get test and sanitizer coverage, not to
	get accurate measurements.

	.. option:: LIBCXX_BENCHMARK_NATIVE_STDLIB:STRING

	Default:: ``""``

	Values:: ``libc++``, ``libstdc++``

	Build the libc++ benchmark tests and Google Benchmark library against the
	specified standard library on the platform. On linux this can be used to
	compare libc++ to libstdc++ by building the benchmark tests against both
	standard libraries.

	.. option:: LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN:STRING

	Use the specified GCC toolchain and standard library when building the native
	stdlib benchmark tests.

	.. option:: LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT:BOOL

	Default: ``OFF``

	Pick the default for whether to constrain ABI-unstable symbols to
	each individual translation unit. This setting controls whether
	`_LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT` is defined by default --
	see the documentation of that macro for details.


	libc++ ABI Feature Options
	--------------------------

	The following options allow building libc++ for a different ABI version.

	.. option:: LIBCXX_ABI_VERSION:STRING

	Default: ``1``

	Defines the target ABI version of libc++.

	.. option:: LIBCXX_ABI_UNSTABLE:BOOL

	Default: ``OFF``

	Build the "unstable" ABI version of libc++. Includes all ABI changing features
	on top of the current stable version.

	.. option:: LIBCXX_ABI_NAMESPACE:STRING

	Default: ``__n`` where ``n`` is the current ABI version.

	This option defines the name of the inline ABI versioning namespace. It can be used for building
	custom versions of libc++ with unique symbol names in order to prevent conflicts or ODR issues
	with other libc++ versions.

	.. warning::
	When providing a custom namespace, it's the users responsibility to ensure the name won't cause
	conflicts with other names defined by libc++, both now and in the future. In particular, inline
	namespaces of the form ``__[0-9]+`` are strictly reserved by libc++ and may not be used by users.
	Doing otherwise could cause conflicts and hinder libc++ ABI evolution.

	.. option:: LIBCXX_ABI_DEFINES:STRING

	Default: ``""``

	A semicolon-separated list of ABI macros to persist in the site config header.
	See ``include/__config`` for the list of ABI macros.


	.. option:: LIBCXX_HAS_MERGED_TYPEINFO_NAMES_DEFAULT

	Default: ``None``. When defined this option overrides the libraries default configuration
	for whether merged type info names are present.


	Build ``std::type_info`` with the assumption that type info names for a type have been fully
	merged are unique across the entire program. This may not be the case for libraries built with
	``-Bsymbolic`` or due to compiler or linker bugs (Ex. llvm.org/PR37398).

	When the value is ``ON`` typeinfo comparisons compare only the pointer value, otherwise ``strcmp``
	is used as a fallback.


	.. _LLVM-specific variables:

	LLVM-specific options
	---------------------

	.. option:: LLVM_LIBDIR_SUFFIX:STRING

	Extra suffix to append to the directory where libraries are to be
	installed. On a 64-bit architecture, one could use ``-DLLVM_LIBDIR_SUFFIX=64``
	to install libraries to ``/usr/lib64``.

	.. option:: LLVM_BUILD_32_BITS:BOOL

	Build 32-bits executables and libraries on 64-bits systems. This option is
	available only on some 64-bits unix systems. Defaults to OFF.

	.. option:: LLVM_LIT_ARGS:STRING

	Arguments given to lit. ``make check`` and ``make clang-test`` are affected.
	By default, ``'-sv --no-progress-bar'`` on Visual C++ and Xcode, ``'-sv'`` on
	others.


	Using Alternate ABI libraries
	=============================


	.. _libsupcxx:

	Using libsupc++ on Linux
	------------------------

	You will need libstdc++ in order to provide libsupc++.

	Figure out where the libsupc++ headers are on your system. On Ubuntu this
	is ``/usr/include/c++/<version>`` and ``/usr/include/c++/<version>/<target-triple>``

	You can also figure this out by running

	.. code-block:: bash

	$ echo \| g++ -Wp,-v -x c++ - -fsyntax-only
	ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
	ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
	#include "..." search starts here:
	#include <...> search starts here:
	/usr/include/c++/4.7
	/usr/include/c++/4.7/x86_64-linux-gnu
	/usr/include/c++/4.7/backward
	/usr/lib/gcc/x86_64-linux-gnu/4.7/include
	/usr/local/include
	/usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
	/usr/include/x86_64-linux-gnu
	/usr/include
	End of search list.

	Note that the first two entries happen to be what we are looking for. This
	may not be correct on other platforms.

	We can now run CMake:

	.. code-block:: bash

	$ CC=clang CXX=clang++ cmake -G "Unix Makefiles" \
	-DLIBCXX_CXX_ABI=libstdc++ \
	-DLIBCXX_CXX_ABI_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/" \
	-DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr \
	<libc++-source-dir>


	You can also substitute ``-DLIBCXX_CXX_ABI=libsupc++``
	above, which will cause the library to be linked to libsupc++ instead
	of libstdc++, but this is only recommended if you know that you will
	never need to link against libstdc++ in the same executable as libc++.
	GCC ships libsupc++ separately but only as a static library. If a
	program also needs to link against libstdc++, it will provide its
	own copy of libsupc++ and this can lead to subtle problems.

	.. code-block:: bash

	$ make cxx
	$ make install

	You can now run clang with -stdlib=libc++.


	.. _libcxxrt_ref:

	Using libcxxrt on Linux
	------------------------

	You will need to keep the source tree of `libcxxrt`_ available
	on your build machine and your copy of the libcxxrt shared library must
	be placed where your linker will find it.

	We can now run CMake like:

	.. code-block:: bash

	$ CC=clang CXX=clang++ cmake -G "Unix Makefiles" \
	-DLIBCXX_CXX_ABI=libcxxrt \
	-DLIBCXX_CXX_ABI_INCLUDE_PATHS=path/to/libcxxrt-sources/src \
	-DCMAKE_BUILD_TYPE=Release \
	-DCMAKE_INSTALL_PREFIX=/usr \
	<libc++-source-directory>
	$ make cxx
	$ make install

	Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
	clang is set up to link for libc++ linked to libsupc++. To get around this
	you'll have to set up your linker yourself (or patch clang). For example,

	.. code-block:: bash

	$ clang++ -stdlib=libc++ helloworld.cpp \
	-nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc

	Alternately, you could just add libcxxrt to your libraries list, which in most
	situations will give the same result:

	.. code-block:: bash

	$ clang++ -stdlib=libc++ helloworld.cpp -lcxxrt

	.. _`libcxxrt`: https://github.com/pathscale/libcxxrt/


	Using a local ABI library installation
	---------------------------------------

	.. warning::
	This is not recommended in almost all cases.

	These instructions should only be used when you can't install your ABI library.

	Normally you must link libc++ against a ABI shared library that the
	linker can find. If you want to build and test libc++ against an ABI
	library not in the linker's path you needq to set
	``-DLIBCXX_CXX_ABI_LIBRARY_PATH=/path/to/abi/lib`` when configuring CMake.

	An example build using libc++abi would look like:

	.. code-block:: bash

	$ CC=clang CXX=clang++ cmake \
	-DLIBCXX_CXX_ABI=libc++abi \
	-DLIBCXX_CXX_ABI_INCLUDE_PATHS="/path/to/libcxxabi/include" \
	-DLIBCXX_CXX_ABI_LIBRARY_PATH="/path/to/libcxxabi-build/lib" \
	path/to/libcxx
	$ make

	When testing libc++ LIT will automatically link against the proper ABI
	library.