[CMake][lldb] add_lldb_library's functions require default visibility

[radford]

Summary

Compiling lldb, in a cmake sub-project that compiles with visibility
hidden, will generate a "cannot export hidden symbol" error because we
require default visibility. Even though we export using
-Wl,-exported_symbols_list,liblldb.exports, if each .cpp file is
compiled with -fvisibility=hidden, then you'll get this warning and
linking will fail. Essentially -exported_symbols_list is not strong
enough to reverse the -fvisibility=hidden.

[labath]

Is there a way to address this through the preprocessor? We already have the LLDB_API macro, which expands to __declspec(dllexport/import) on windows. Would expanding it do __attribute__((visibility("default"))) (or something) on other platforms help with anything?

[radford]

Yes, this IMO should eventually be addressed by explicitly exporting each meant-to-be-exported function with LLDB_ABI and then changing the line this patch adds to use hidden instead of default.

This patch is meant to be a band-aid until that can be done.

lldb/cmake/modules/AddLLDB.cmake

llvm_add_library(${name} ${libkind} ${srcs}
       ${pass_NO_INSTALL_RPATH}
     )
 
     if(CLANG_LINK_CLANG_DYLIB)
       target_link_libraries(${name} PRIVATE clang-cpp)
     else()
       target_link_libraries(${name} PRIVATE ${PARAM_CLANG_LIBS})
     endif()
+    set_target_properties(${name} PROPERTIES CXX_VISIBILITY_PRESET default)
   endif()
 
   # A target cannot be changed to a FRAMEWORK after calling install() because
   # this may result in the wrong install DESTINATION. The FRAMEWORK property
   # must be set earlier.
   if(PARAM_FRAMEWORK)
     set_target_properties(liblldb PROPERTIES FRAMEWORK ON)
   endif()