[libcxx] Fix libc++ re-exporting logic when Command Line Tools are not installed

[ldionne]

Summary

When the Xcode Command Line tools are not installed but CMAKE_OSX_SYSROOT is
set, we would try to re-export symbols from the libc++abi.dylib shipped in
the sysroot, which does not exist. This commit changes the build on OS X to
always re-export symbols from the explicit re-export lists, which doesn't
change depending on what system you're building on, and is therefore much
less flaky.

[ldionne]

I tested this on Mojave and High Sierra with and without developer tools installed, but I would appreciate if reviewers could pull this patch, run ninja check-cxx-abilist and make sure it passes.

[smeenai]

check-cxx-abilist passes for me with this applied (Mojave, Xcode 10.1).

[ldionne]

In D54595#1300408, @smeenai wrote:

check-cxx-abilist passes for me with this applied (Mojave, Xcode 10.1).

Thanks for checking!

libcxx/trunk/lib/CMakeLists.txt

 
 if (LIBCXX_GENERATE_COVERAGE AND NOT LIBCXX_COVERAGE_LIBRARY)
   find_compiler_rt_library(profile LIBCXX_COVERAGE_LIBRARY)
 endif()
 add_library_flags_if(LIBCXX_COVERAGE_LIBRARY "${LIBCXX_COVERAGE_LIBRARY}")
 
 if (APPLE AND (LIBCXX_CXX_ABI_LIBNAME STREQUAL "libcxxabi" OR
                LIBCXX_CXX_ABI_LIBNAME STREQUAL "default"))
-  set(LIBCXX_OSX_REEXPORT_SYSTEM_ABI_LIBRARY ON)
+  set(LIBCXX_OSX_REEXPORT_LIBCXXABI_SYMBOLS ON)
 endif()
 
 if (LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY)
   add_library_flags("-Wl,--whole-archive" "-Wl,-Bstatic")
   add_library_flags("${LIBCXX_CXX_ABI_LIBRARY}")
   add_library_flags("-Wl,-Bdynamic" "-Wl,--no-whole-archive")
-elseif (LIBCXX_OSX_REEXPORT_SYSTEM_ABI_LIBRARY)
+elseif (LIBCXX_OSX_REEXPORT_LIBCXXABI_SYMBOLS)
   add_library_flags("${LIBCXX_CXX_ABI_LIBRARY}")
 else ()
  add_interface_library("${LIBCXX_CXX_ABI_LIBRARY}")
 endif()
 
 if (APPLE AND LLVM_USE_SANITIZER)
   if (("${LLVM_USE_SANITIZER}" STREQUAL "Address") OR
       ("${LLVM_USE_SANITIZER}" STREQUAL "Address;Undefined") OR
if (LIBCXX_TARGETING_MSVC)
   add_library_flags(vcruntime${LIB_SUFFIX}) # C++ runtime
   add_library_flags(msvcrt${LIB_SUFFIX}) # C runtime startup files
   add_library_flags(msvcprt${LIB_SUFFIX}) # C++ standard library. Required for exception_ptr internals.
   # Required for standards-complaint wide character formatting functions
   # (e.g. `printfw`/`scanfw`)
   add_library_flags(iso_stdio_wide_specifiers)
 endif()
 
-if (LIBCXX_OSX_REEXPORT_SYSTEM_ABI_LIBRARY)
+if (LIBCXX_OSX_REEXPORT_LIBCXXABI_SYMBOLS)
   if (NOT DEFINED LIBCXX_LIBCPPABI_VERSION)
     set(LIBCXX_LIBCPPABI_VERSION "2") # Default value
     execute_process(
       COMMAND xcrun --show-sdk-version
       OUTPUT_VARIABLE sdk_ver
       RESULT_VARIABLE res
       OUTPUT_STRIP_TRAILING_WHITESPACE)
     if (res EQUAL 0)
       message(STATUS "Found SDK version ${sdk_ver}")
       string(REPLACE "10." "" sdk_ver "${sdk_ver}")
       if (sdk_ver LESS 9)
         set(LIBCXX_LIBCPPABI_VERSION "")
       else()
         set(LIBCXX_LIBCPPABI_VERSION "2")
       endif()
     endif()
   endif()
 
   if ( CMAKE_OSX_DEPLOYMENT_TARGET STREQUAL "10.6" )
     message(FATAL_ERROR "Mac OSX 10.6 is not supported anymore as a deployment "
                         "target. If you need support for this, please contact "
                         "the libc++ maintainers.")
   else()
-    if (DEFINED CMAKE_OSX_SYSROOT AND NOT CMAKE_OSX_SYSROOT STREQUAL "")
-      list(FIND CMAKE_OSX_ARCHITECTURES "armv7" OSX_HAS_ARMV7)
-      if (NOT OSX_HAS_ARMV7 EQUAL -1)
-        set(OSX_RE_EXPORT_LINE
-          "${CMAKE_OSX_SYSROOT}/usr/lib/libc++abi.dylib"
-          "-Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++sjlj-abi.exp")
-      else()
-        set(OSX_RE_EXPORT_LINE
-          "-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${LIBCXX_LIBCPPABI_VERSION}.exp")
-      if (NOT LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS)
-        add_link_flags("/usr/lib/libc++abi.dylib -Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++abi-new-delete.exp")
-      endif()
+    if ("armv7" IN_LIST CMAKE_OSX_ARCHITECTURES)
+      set(RE_EXPORT_LIST "${CMAKE_CURRENT_SOURCE_DIR}/libc++sjlj-abi.exp")
+      set(RE_EXPORT_LIST "${CMAKE_CURRENT_SOURCE_DIR}/libc++abi${LIBCXX_LIBCPPABI_VERSION}.exp")
     endif()
     add_link_flags(
       "-compatibility_version 1"
       "-install_name /usr/lib/libc++.1.dylib"
       "-Wl,-unexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++unexp.exp"
-      "${OSX_RE_EXPORT_LINE}"
+      "-Wl,-reexported_symbols_list,${RE_EXPORT_LIST}"
       "-Wl,-force_symbols_not_weak_list,${CMAKE_CURRENT_SOURCE_DIR}/notweak.exp"
       "-Wl,-force_symbols_weak_list,${CMAKE_CURRENT_SOURCE_DIR}/weak.exp")
+
+    if (NOT LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS)
+      add_link_flags("-Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++abi-new-delete.exp")
+    endif()
   endif()
 endif()
 
 split_list(LIBCXX_COMPILE_FLAGS)
 split_list(LIBCXX_LINK_FLAGS)
 
 # Add an object library that contains the compiled source files.
 add_library(cxx_objects OBJECT ${exclude_from_all} ${LIBCXX_SOURCES} ${LIBCXX_HEADERS})