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.. _BuildingLibcxx:
Building libc++
.. contents::
.. _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 <>`_ 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``
$ 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 \
$ 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" ^
> 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_C_FLAGS="-fms-compatibility-version=19.00 --target=i686--windows" ^
-DCMAKE_CXX_FLAGS="-fms-compatibility-version=19.00 --target=i686--windows" ^
-DLLVM_PATH=/path/to/llvm/tree ^
> /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`:
.. _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``.
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.
Path where LLVM will be installed if "make install" is invoked or the
"INSTALL" target is built.
The C++ compiler to use when building and testing libc++.
.. _libcxx-specific options:
libc++ specific options
**Default**: ``ON``
Toggle the installation of the library portion of libc++.
**Default**: ``ON``
Toggle the installation of the libc++ headers.
**Default**: ``ON``
Build libc++ with assertions enabled.
**Default**: ``OFF``
Build libc++ as a 32 bit library. Also see `LLVM_BUILD_32_BITS`.
**Default**: ``ON``
Build libc++ as a shared library. Either `LIBCXX_ENABLE_SHARED` or
`LIBCXX_ENABLE_STATIC` has to be enabled.
**Default**: ``ON``
Build libc++ as a static library. Either `LIBCXX_ENABLE_SHARED` or
`LIBCXX_ENABLE_STATIC` has to be enabled.
Extra suffix to append to the directory where libraries are to be installed.
This option overrides `LLVM_LIBDIR_SUFFIX`.
**Default**: ``""``
Define libc++ destination prefix.
**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.
**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
**Default**: ``ON``
Build and test libc++experimental.a.
Install libc++experimental.a alongside libc++.
.. _ABI Library Specific Options:
ABI Library Specific Options
**Values**: ``none``, ``libcxxabi``, ``libcxxrt``, ``libstdc++``, ``libsupc++``.
Select the ABI library to build libc++ against.
Provide additional search paths for the ABI library headers.
Provide the path to the ABI library that libc++ should link against.
**Default**: ``OFF``
If this option is enabled, libc++ will try and link the selected ABI library
**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 ```` which
links the correct ABI library.
**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
**Default**: ``ON``
Build libc++ with exception support.
**Default**: ``ON``
Build libc++ with run time type information.
**Default**: ``ON`` (or value of ``LLVM_INCLUDE_DIR``)
Build the libc++ tests.
**Default**: ``ON``
Build the libc++ benchmark tests and the Google Benchmark library needed
to support them.
**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.
**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.
Use the specified GCC toolchain and standard library when building the native
stdlib benchmark tests.
**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.
**Default**: ``1``
Defines the target ABI version of libc++.
**Default**: ``OFF``
Build the "unstable" ABI version of libc++. Includes all ABI changing features
on top of the current stable version.
**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.
**Default**: ``""``
A semicolon-separated list of ABI macros to persist in the site config header.
See ``include/__config`` for the list of ABI macros.
**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.
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
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.
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
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:
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/" \
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 \
$ 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`:
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" \
$ make
When testing libc++ LIT will automatically link against the proper ABI