[Bug 215193] libc++ and libcxxrt: convert to a private library

From: <bugzilla-noreply_at_freebsd.org>
Date: Wed, 08 Dec 2021 21:07:16 UTC

Mark Millard <marklmi26-fbsd@yahoo.com> changed:

           What    |Removed                     |Added
                 CC|                            |marklmi26-fbsd@yahoo.com

--- Comment #5 from Mark Millard <marklmi26-fbsd@yahoo.com> ---
(In reply to David Chisnall from comment #2)

For reference:


reports .  . .

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.

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