1*58b9f456SAndroid Build Coastguard Worker 2*58b9f456SAndroid Build Coastguard Worker==================== 3*58b9f456SAndroid Build Coastguard WorkerLibc++ ABI stability 4*58b9f456SAndroid Build Coastguard Worker==================== 5*58b9f456SAndroid Build Coastguard Worker 6*58b9f456SAndroid Build Coastguard WorkerLibc++ aims to preserve stable ABI to avoid subtle bugs when code built to the old ABI 7*58b9f456SAndroid Build Coastguard Workeris linked with the code build to the new ABI. At the same time, libc++ allows ABI-breaking 8*58b9f456SAndroid Build Coastguard Workerimprovements and bugfixes for the scenarios when ABI change is not a issue. 9*58b9f456SAndroid Build Coastguard Worker 10*58b9f456SAndroid Build Coastguard WorkerTo support both cases, libc++ allows specifying the ABI version at the 11*58b9f456SAndroid Build Coastguard Workerbuild time. The version is defined with a cmake option 12*58b9f456SAndroid Build Coastguard WorkerLIBCXX_ABI_VERSION. Another option LIBCXX_ABI_UNSTABLE can be used to 13*58b9f456SAndroid Build Coastguard Workerinclude all present ABI breaking features. These options translate 14*58b9f456SAndroid Build Coastguard Workerinto C++ macro definitions _LIBCPP_ABI_VERSION, _LIBCPP_ABI_UNSTABLE. 15*58b9f456SAndroid Build Coastguard Worker 16*58b9f456SAndroid Build Coastguard WorkerAny ABI-changing feature is placed under it's own macro, _LIBCPP_ABI_XXX, which is enabled 17*58b9f456SAndroid Build Coastguard Workerbased on the value of _LIBCPP_ABI_VERSION. _LIBCPP_ABI_UNSTABLE, if set, enables all features at once. 18