build: hide symbols using CMake

This uses the CMake settings to correctly select the visibility
attribute for the runtime.

Author: compnerd

stdlib/CMakeLists.txt

@@ -24,6 +24,10 @@ set(CMAKE_CXX_IMPLICIT_LINK_LIBRARIES "")
 set(CMAKE_C_IMPLICIT_LINK_DIRECTORIES "")
 set(CMAKE_CXX_IMPLICIT_LINK_DIRECTORIES "")
 
+set(CMAKE_C_VISIBILITY_PRESET hidden)
+set(CMAKE_CXX_VISIBILITY_PRESET hidden)
+set(CMAKE_VISIBILITY_INLINES_HIDDEN YES)
+
 if(SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER)
   if(NOT "${CMAKE_C_COMPILER_ID}" MATCHES "Clang")
     message(FATAL_ERROR "Building the swift runtime is not supported with ${CMAKE_C_COMPILER_ID}. Use the just-built clang instead.")

stdlib/public/CMakeLists.txt

@@ -48,13 +48,6 @@ if(CXX_SUPPORTS_EXIT_TIME_DESTRUCTORS_WARNING)
   list(APPEND SWIFT_RUNTIME_CORE_CXX_FLAGS "-Wexit-time-destructors")
 endif()
 
-# We don't want runtime C++ code to export symbols we didn't explicitly
-# choose to.
-check_cxx_compiler_flag("-fvisibility=hidden" CXX_SUPPORTS_DEFAULT_HIDDEN_VISIBILITY)
-if(CXX_SUPPORTS_DEFAULT_HIDDEN_VISIBILITY)
-  list(APPEND SWIFT_RUNTIME_CORE_CXX_FLAGS "-fvisibility=hidden")
-endif()
-
 add_subdirectory(SwiftShims)
 
 if(SWIFT_BUILD_STDLIB)

stdlib/toolchain/CMakeLists.txt

@@ -15,11 +15,7 @@ set(compile_flags
   # C++ code in the runtime and standard library should generally avoid
   # introducing static constructors or destructors.
   "-Wglobal-constructors"
-  "-Wexit-time-destructors"
-
-  # We don't want runtime C++ code to export symbols we didn't explicitly
-  # choose to.
-  "-fvisibility=hidden")
+  "-Wexit-time-destructors")
 
 
 # Build the runtime with -Wall to catch, e.g., uninitialized variables