25 lines
1.2 KiB
ReStructuredText
25 lines
1.2 KiB
ReStructuredText
|
|
====================
|
|
Libc++ ABI stability
|
|
====================
|
|
|
|
Libc++ aims to preserve a stable ABI to avoid subtle bugs when code built under the old ABI
|
|
is linked with code built under the new ABI. At the same time, libc++ wants to make
|
|
ABI-breaking improvements and bugfixes in scenarios where the user doesn't mind ABI breaks.
|
|
|
|
To support both cases, libc++ allows specifying an ABI version at
|
|
build time. The version is defined with CMake option ``LIBCXX_ABI_VERSION``.
|
|
Currently supported values are ``1`` (the stable default)
|
|
and ``2`` (the unstable "next" version). At some point "ABI version 2" will be
|
|
frozen and new ABI-breaking changes will start being applied to version ``3``;
|
|
but this has not happened yet.
|
|
|
|
To always use the most cutting-edge, most unstable ABI (which is currently ``2``
|
|
but at some point will become ``3``), set the CMake option ``LIBCXX_ABI_UNSTABLE``.
|
|
|
|
Internally, each ABI-changing feature is placed under its own C++ macro,
|
|
``_LIBCPP_ABI_XXX``. These macros' definitions are controlled by the C++ macro
|
|
``_LIBCPP_ABI_VERSION``, which is controlled by the ``LIBCXX_ABI_VERSION`` set
|
|
at build time. Libc++ does not intend users to interact with these C++ macros
|
|
directly.
|