[libcxx] Reexport std::bad_array_length symbols from libc++abi on OS X.

[EricWF]

Summary

On OS X libc++ needs to reexport libc++abi's symbols in order for them to be provided. We explicitly list the symbols to reexport it libcxx/lib/libc++abi2.exp. This patch adds the symbols required by std::bad_array_length which have been missing for some time.

However there is a problem. std::bad_array_length was add to libc++abi in September of 2013 by commit r190479, about a year after everything else. Therefore I think older OS X version have libc++abi versions without std::bad_array_length. On those systems
libc++ won't build with this change because we will try and export undefined symbols.

The workaround I would write to support older systems depends on the amount of people who would need it. If only a small number of developers are affected it might be sufficient to provide a CMake switch like LIBCPP_LIBCPPABI_HAS_BAD_ARRAY_LENGTH which is
ON by default and can be disabled by those who need it. Otherwise I think we should try to automatically detect if the symbols are present in /usr/lib/libc++abi.dylib and configure accordingly. I would prefer the first solution because writing CMake sucks.

[aprantl]

Grepping through the nm output of libc++abi it looks like bad_array_length is included in Xcode 7 and Xcode 6.4, which is also what is installed on the lab.llvm.org:8080 machines and going further back it looks like it is even included in MacOSX10.9.sdk in Xcode 5.1.1.

I don't think there are any expectation that LLVM trunk can be built with older versions.

Thanks for investigating this!

[EricWF]

I moved the symbols into lib/libc++abi2.exp since we didn't anticipate the need to exclude them.

lib/CMakeLists.txt

           "-Wl,-reexport_library,${CMAKE_OSX_SYSROOT}/usr/lib/libc++abi.dylib")
       endif()
     else()
-      set (OSX_RE_EXPORT_LINE "/usr/lib/libc++abi.dylib -Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++abi${LIBCXX_LIBCPPABI_VERSION}.exp")
+      set(OSX_RE_EXPORT_LINE "/usr/lib/libc++abi.dylib -Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++abi${LIBCXX_LIBCPPABI_VERSION}.exp")
+      set(OSX_RE_EXPORT_LINE "${OSX_RE_EXPORT_LINE} -Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++abi_bad_array_length.exp")
     endif()
 
     add_link_flags(

lib/libc++abi_bad_array_length.exp

+__ZNKSt16bad_array_length4whatEv
+__ZNSt16bad_array_lengthC1Ev
+__ZNSt16bad_array_lengthC2Ev
+__ZNSt16bad_array_lengthD0Ev
+__ZNSt16bad_array_lengthD1Ev
+__ZNSt16bad_array_lengthD2Ev
+__ZTISt16bad_array_length
+__ZTSSt16bad_array_length
+__ZTVSt16bad_array_length