1# This function defines a linker script in place of the symlink traditionally
2# created for shared libraries.
3#
4# More specifically, this function goes through the PUBLIC and INTERFACE
5# library dependencies of <target> and gathers them into a linker script,
6# such that those libraries are linked against when the shared library for
7# <target> is linked against.
8#
9# Arguments:
10#   <target>: A target representing a shared library. A linker script will be
11#             created in place of that target's TARGET_LINKER_FILE, which is
12#             the symlink pointing to the actual shared library (usually
13#             libFoo.so pointing to libFoo.so.1, which itself points to
14#             libFoo.so.1.0).
15
16function(define_linker_script target)
17  if (NOT TARGET "${target}")
18    message(FATAL_ERROR "The provided target '${target}' is not actually a target.")
19  endif()
20
21  get_target_property(target_type "${target}" TYPE)
22  if (NOT "${target_type}" STREQUAL "SHARED_LIBRARY")
23    message(FATAL_ERROR "The provided target '${target}' is not a shared library (its type is '${target_type}').")
24  endif()
25
26  set(symlink "$<TARGET_LINKER_FILE:${target}>")
27  set(soname "$<TARGET_SONAME_FILE_NAME:${target}>")
28
29  get_target_property(interface_libs "${target}" INTERFACE_LINK_LIBRARIES)
30
31  set(link_libraries)
32  if (interface_libs)
33    foreach(lib IN LISTS interface_libs)
34      if ("${lib}" STREQUAL "cxx-headers")
35        continue()
36      endif()
37      # If ${lib} is not a target, we use a dummy target which we know will
38      # have an OUTPUT_NAME property so that CMake doesn't fail when evaluating
39      # the non-selected branch of the `IF`. It doesn't matter what it evaluates
40      # to because it's not selected, but it must not cause an error.
41      # See https://gitlab.kitware.com/cmake/cmake/-/issues/21045.
42      set(output_name_tgt "$<IF:$<TARGET_EXISTS:${lib}>,${lib},${target}>")
43      set(libname "$<IF:$<TARGET_EXISTS:${lib}>,$<TARGET_PROPERTY:${output_name_tgt},OUTPUT_NAME>,${lib}>")
44      list(APPEND link_libraries "${CMAKE_LINK_LIBRARY_FLAG}${libname}")
45    endforeach()
46  endif()
47  string(REPLACE ";" " " link_libraries "${link_libraries}")
48
49  set(linker_script "INPUT(${soname} ${link_libraries})")
50  add_custom_command(TARGET "${target}" POST_BUILD
51    COMMAND "${CMAKE_COMMAND}" -E remove "${symlink}"
52    COMMAND "${CMAKE_COMMAND}" -E echo "${linker_script}" > "${symlink}"
53    COMMENT "Generating linker script: '${linker_script}' as file ${symlink}"
54    VERBATIM
55  )
56endfunction()
57