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      1  1.1  joerg 
      2  1.1  joerg ====================
      3  1.1  joerg Libc++ ABI stability
      4  1.1  joerg ====================
      5  1.1  joerg 
      6  1.1  joerg Libc++ aims to preserve stable ABI to avoid subtle bugs when code built to the old ABI
      7  1.1  joerg is linked with the code build to the new ABI. At the same time, libc++ allows ABI-breaking
      8  1.1  joerg improvements and bugfixes for the scenarios when ABI change is not a issue.
      9  1.1  joerg 
     10  1.1  joerg To support both cases, libc++ allows specifying the ABI version at the
     11  1.1  joerg build time.  The version is defined with a cmake option
     12  1.1  joerg LIBCXX_ABI_VERSION. Another option LIBCXX_ABI_UNSTABLE can be used to
     13  1.1  joerg include all present ABI breaking features. These options translate
     14  1.1  joerg into C++ macro definitions _LIBCPP_ABI_VERSION, _LIBCPP_ABI_UNSTABLE.
     15  1.1  joerg 
     16  1.1  joerg Any ABI-changing feature is placed under it's own macro, _LIBCPP_ABI_XXX, which is enabled
     17  1.1  joerg based on the value of _LIBCPP_ABI_VERSION. _LIBCPP_ABI_UNSTABLE, if set, enables all features at once.
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