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#
# - This module provides the function
# itk_target_link_libraries_with_dynamic_lookup which can be used to
# "weakly" link loadable module.
#
# Link a library to a target such that the symbols are resolved at
# run-time not link-time. This should be used when compiling a
# loadable module when the symbols should be resolve from the run-time
# environment where the module is loaded, and not a specific system
# library.
#
# Specifically, for OSX it uses undefined dynamic_lookup. This is
# simular to using "-shared" on Linux where undefined symbols are
# ignored.
#
# Additionally, the linker is checked to see if it supports undefined
# symbols when linking a shared library. If it does then the library
# is not linked when specified with this function.
#
# http://blog.tim-smith.us/2015/09/python-extension-modules-os-x/
#
# Function: _itkCheckUndefinedSymbolsAllowed
#
# Check if the linker allows undefined symbols for shared libraries.
#
# ITK_UNDEFINED_SYMBOLS_ALLOWED - true if the linker will allow
# undefined symbols for shared libraries
#
function(_itkCheckUndefinedSymbolsAllowed)
set(VARIABLE "ITK_UNDEFINED_SYMBOLS_ALLOWED")
set(cache_var "${VARIABLE}_hash")
# hash the CMAKE_FLAGS passed and check cache to know if we need to rerun
string(MD5 cmake_flags_hash "${CMAKE_SHARED_LINKER_FLAGS}")
if(NOT DEFINED "${cache_var}" )
unset("${VARIABLE}" CACHE)
elseif(NOT "${${cache_var}}" STREQUAL "${cmake_flags_hash}" )
unset("${VARIABLE}" CACHE)
endif()
if(NOT DEFINED "${VARIABLE}")
set(test_project_dir "${PROJECT_BINARY_DIR}/CMakeTmp/${VARIABLE}")
file(WRITE "${test_project_dir}/CMakeLists.txt"
"
project(undefined C)
add_library(foo SHARED \"foo.c\")
")
file(WRITE "${test_project_dir}/foo.c"
"
extern int bar(void);
int foo(void) {return bar()+1;}
")
# ITK requires CMake >= 2.8.12. Before that, on APPLE, no flag should be passed.
set( _rpath_arg "-DCMAKE_MACOSX_RPATH='${CMAKE_MACOSX_RPATH}'" )
try_compile(${VARIABLE}
"${test_project_dir}"
"${test_project_dir}"
undefined
CMAKE_FLAGS
"-DCMAKE_SHARED_LINKER_FLAGS='${CMAKE_SHARED_LINKER_FLAGS}'"
${_rpath_arg}
OUTPUT_VARIABLE output)
set(${cache_var} "${cmake_flags_hash}" CACHE INTERNAL "hashed try_compile flags")
if(${VARIABLE})
message(STATUS "Performing Test ${VARIABLE} - Success")
else()
message(STATUS "Performing Test ${VARIABLE} - Failed")
file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
"Performing Test ${VARIABLE} failed with the following output:\n"
"${OUTPUT}\n")
endif()
endif()
endfunction()
_itkCheckUndefinedSymbolsAllowed()
macro( itk_target_link_libraries_with_dynamic_lookup target )
if ( ${CMAKE_SYSTEM_NAME} MATCHES "Darwin" )
set_target_properties( ${target} PROPERTIES LINK_FLAGS "-undefined dynamic_lookup" )
elseif(ITK_UNDEFINED_SYMBOLS_ALLOWED)
# linker allows undefined symbols, let's just not link
else()
target_link_libraries ( ${target} ${ARGN} )
endif()
endmacro()
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