[libc++] Move the linker script generation step to CMake

Summary:
This allows the linker script generation to query CMake properties
(specifically the dependencies of libc++.so) instead of having to
carry these dependencies around manually in global variables. Notice
the removal of the LIBCXX_INTERFACE_LIBRARIES global variable.

Reviewers: phosek, EricWF

Subscribers: mgorny, christof, jkorous, dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D68343

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@374116 91177308-0d34-0410-b5e6-96231b3b80d8

Author: ldionne

CMakeLists.txt

@@ -380,9 +380,6 @@ if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
     if (APPLE)
       message(FATAL_ERROR "LIBCXX_ENABLE_ABI_LINKER_SCRIPT cannot be used on APPLE targets")
     endif()
-    if (NOT PYTHONINTERP_FOUND)
-      message(FATAL_ERROR "LIBCXX_ENABLE_ABI_LINKER_SCRIPT requires python but it was not found.")
-    endif()
     if (NOT LIBCXX_ENABLE_SHARED)
       message(FATAL_ERROR "LIBCXX_ENABLE_ABI_LINKER_SCRIPT is only available for shared library builds.")
     endif()
@@ -447,12 +444,9 @@ set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${LIBCXX_LIBRARY_DIR})
 # LIBCXX_COMPILE_FLAGS: Compile only flags.
 # LIBCXX_LINK_FLAGS: Linker only flags.
 # LIBCXX_LIBRARIES: libraries libc++ is linked to.
-# LIBCXX_INTERFACE_LIBRARIES: Libraries that must be linked when using libc++
-#                             These libraries are exposed in the linker script.
 set(LIBCXX_COMPILE_FLAGS "")
 set(LIBCXX_LINK_FLAGS "")
 set(LIBCXX_LIBRARIES "")
-set(LIBCXX_INTERFACE_LIBRARIES "")
 
 # Include macros for adding and removing libc++ flags.
 include(HandleLibcxxFlags)

cmake/Modules/DefineLinkerScript.cmake

@@ -0,0 +1,50 @@
+# This function defines a linker script in place of the symlink traditionally
+# created for shared libraries.
+#
+# More specifically, this function goes through the PUBLIC and INTERFACE
+# library dependencies of <target> and gathers them into a linker script,
+# such that those libraries are linked against when the shared library for
+# <target> is linked against.
+#
+# Arguments:
+#   <target>: A target representing a shared library. A linker script will be
+#             created in place of that target's TARGET_LINKER_FILE, which is
+#             the symlink pointing to the actual shared library (usually
+#             libFoo.so pointing to libFoo.so.1, which itself points to
+#             libFoo.so.1.0).
+
+function(define_linker_script target)
+  if (NOT TARGET "${target}")
+    message(FATAL_ERROR "The provided target '${target}' is not actually a target.")
+  endif()
+
+  get_target_property(target_type "${target}" TYPE)
+  if (NOT "${target_type}" STREQUAL "SHARED_LIBRARY")
+    message(FATAL_ERROR "The provided target '${target}' is not a shared library (its type is '${target_type}').")
+  endif()
+
+  set(symlink "$<TARGET_LINKER_FILE:${target}>")
+  set(soname "$<TARGET_SONAME_FILE_NAME:${target}>")
+
+  get_target_property(interface_libs "${target}" INTERFACE_LINK_LIBRARIES)
+
+  set(link_libraries)
+  if (interface_libs)
+    foreach(lib IN LISTS interface_libs)
+      if (TARGET "${lib}")
+        list(APPEND link_libraries "${CMAKE_LINK_LIBRARY_FLAG}$<TARGET_PROPERTY:${lib},OUTPUT_NAME>")
+      else()
+        list(APPEND link_libraries "${CMAKE_LINK_LIBRARY_FLAG}${lib}")
+      endif()
+    endforeach()
+  endif()
+  list(JOIN link_libraries " " link_libraries)
+
+  set(linker_script "INPUT(${soname} ${link_libraries})")
+  add_custom_command(TARGET "${target}" POST_BUILD
+    COMMAND "${CMAKE_COMMAND}" -E remove "${symlink}"
+    COMMAND "${CMAKE_COMMAND}" -E echo "${linker_script}" > "${symlink}"
+    COMMENT "Generating linker script: '${linker_script}' as file ${symlink}"
+    VERBATIM
+  )
+endfunction()

src/CMakeLists.txt

@@ -177,12 +177,10 @@ if (LIBCXX_ENABLE_SHARED)
   if (LIBCXXABI_USE_LLVM_UNWINDER)
     if (NOT LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_SHARED_LIBRARY AND (TARGET unwind_shared OR HAVE_LIBUNWIND))
       target_link_libraries(cxx_shared PUBLIC unwind_shared)
-      list(APPEND LIBCXX_INTERFACE_LIBRARIES unwind_shared) # For the linker script
     elseif (LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_SHARED_LIBRARY AND (TARGET unwind_static OR HAVE_LIBUNWIND))
       # libunwind is already included in libc++abi
     else()
-      target_link_libraries(cxx_shared PRIVATE unwind)
-      list(APPEND LIBCXX_INTERFACE_LIBRARIES unwind) # For the linker script
+      target_link_libraries(cxx_shared PUBLIC unwind)
     endif()
   endif()
 
@@ -195,7 +193,6 @@ if (LIBCXX_ENABLE_SHARED)
     endif()
   else()
     target_link_libraries(cxx_shared PUBLIC "${LIBCXX_CXX_SHARED_ABI_LIBRARY}")
-    list(APPEND LIBCXX_INTERFACE_LIBRARIES "${LIBCXX_CXX_SHARED_ABI_LIBRARY}") # For the linker script
   endif()
 
   # Maybe re-export symbols from libc++abi
@@ -222,31 +219,10 @@ if (LIBCXX_ENABLE_SHARED)
     endif()
   endif()
 
-  # Generate a linker script in place of a libc++.so symlink. Rerun this command
-  # after cxx builds.
+  # Generate a linker script in place of a libc++.so symlink.
   if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
-    # Get the name of the ABI library and handle the case where CXXABI_LIBNAME
-    # is a target name and not a library. Ex cxxabi_shared.
-    set(LIBCXX_INTERFACE_LIBRARY_NAMES)
-    foreach(lib ${LIBCXX_INTERFACE_LIBRARIES})
-      # FIXME: Handle cxxabi_static and unwind_static.
-      if (TARGET ${lib} OR
-          (${lib} MATCHES "cxxabi(_static|_shared)?" AND HAVE_LIBCXXABI) OR
-          (${lib} MATCHES "unwind(_static|_shared)?" AND HAVE_LIBUNWIND))
-        list(APPEND LIBCXX_INTERFACE_LIBRARY_NAMES "$<TARGET_PROPERTY:${lib},OUTPUT_NAME>")
-      else()
-        list(APPEND LIBCXX_INTERFACE_LIBRARY_NAMES "${lib}")
-      endif()
-    endforeach()
-    add_custom_command(TARGET cxx_shared POST_BUILD
-      COMMAND
-        ${PYTHON_EXECUTABLE} ${LIBCXX_SOURCE_DIR}/utils/gen_link_script.py
-      ARGS
-        --input "$<TARGET_SONAME_FILE:cxx_shared>"
-        --output "$<TARGET_LINKER_FILE:cxx_shared>"
-        ${LIBCXX_INTERFACE_LIBRARY_NAMES}
-      WORKING_DIRECTORY ${LIBCXX_BUILD_DIR}
-    )
+      include(DefineLinkerScript)
+      define_linker_script(cxx_shared)
   endif()
 
   list(APPEND LIBCXX_BUILD_TARGETS "cxx_shared")