[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

llvm-svn: 374116

1 files changed, 50 insertions, 0 deletions

diff --git a/libcxx/cmake/Modules/DefineLinkerScript.cmake b/libcxx/cmake/Modules/DefineLinkerScript.cmake
new file mode 100644
index 00000000000..2b456a42b30
--- /dev/null
+++ b/libcxx/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()