Revert some changes in light of GCC 4 -fPIE reversal

The -fPIE option is now accepted when using GCC 4, which means it
is available for backward compatibility for clients using
CMake 2.8.11 or older which makes use of the
POSITION_INDEPENDENT_CODE feature.

Conditionally use that feature for old versions of cmake with
GCC 4. Restore the tests for those versions, and clarify the
situation in the ChangeLog.

Change-Id: I5a06b155dda7db559d86841a2b34fd8ed95acbd0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

dist/changes-5.4.2

@@ -37,14 +37,20 @@ information about a particular change.
 - On x86 and x86-64 systems with ELF binaries (especially Linux), due to
   a new optimization in GCC 5.x in combination with a recent version of
   GNU binutils, compiling Qt applications with -fPIE is no longer
-  enough. Applications now need to be compiled with the -fPIC option if
+  enough with GCC 5.x. Applications now need to be compiled with
-  Qt's option "reduce relocations" is active. Note that Clang is known
+  the -fPIC option if Qt's option "reduce relocations" is active. For
-  to generate incompatible code even with -fPIC if the -flto option is
+  backward compatibility only, Qt accepts the use of -fPIE for GCC 4.x
-  active.
+  versions.
+  Note that Clang is known to generate incompatible code even with -fPIC if
+  the -flto option is active.
   Applications using qmake or cmake >= 2.8.12 as their build system will
-  adapt automatically. Applications using an older release of cmake need to
+  adapt automatically. Applications using an older release of cmake in
-  change their CMakeLists.txt to add Qt5Core_EXECUTABLE_COMPILE_FLAGS to
+  combination with GCC 5.x need to change their CMakeLists.txt to add
-  CMAKE_CXX_FLAGS.
+  Qt5Core_EXECUTABLE_COMPILE_FLAGS to CMAKE_CXX_FLAGS. In particular,
+  applications using cmake >= 2.8.9 and < 2.8.11 will continue to build
+  with the -fPIE option and invoke the special compatibility mode if using
+  GCC 4.x.
+
 
 ****************************************************************************
 *                               Library                                    *

src/corelib/Qt5CoreConfigExtras.cmake.in

@@ -71,7 +71,13 @@ set(_qt5_corelib_extra_includes)
 # macro to add it.
 set(Qt5_POSITION_INDEPENDENT_CODE True)
 set(Qt5Core_EXECUTABLE_COMPILE_FLAGS \"-fPIC\")
-set_property(TARGET Qt5::Core APPEND PROPERTY INTERFACE_COMPILE_OPTIONS $$QMAKE_CXXFLAGS_APP)
+if (CMAKE_VERSION VERSION_LESS 2.8.12
+        AND (NOT CMAKE_CXX_COMPILER_ID STREQUAL \"GNU\"
+        OR CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0))
+    set_property(TARGET Qt5::Core APPEND PROPERTY INTERFACE_POSITION_INDEPENDENT_CODE \"ON\")
+else()
+    set_property(TARGET Qt5::Core APPEND PROPERTY INTERFACE_COMPILE_OPTIONS $$QMAKE_CXXFLAGS_APP)
+endif()
 
 !!IF !isEmpty(QT_NAMESPACE)
 list(APPEND Qt5Core_DEFINITIONS -DQT_NAMESPACE=$$QT_NAMESPACE)

src/corelib/Qt5CoreMacros.cmake

@@ -281,6 +281,12 @@ if (NOT CMAKE_VERSION VERSION_LESS 2.8.9)
             set_property(TARGET ${_target} APPEND PROPERTY COMPILE_DEFINITIONS_RELEASE QT_NO_DEBUG)
             set_property(TARGET ${_target} APPEND PROPERTY COMPILE_DEFINITIONS_RELWITHDEBINFO QT_NO_DEBUG)
             set_property(TARGET ${_target} APPEND PROPERTY COMPILE_DEFINITIONS_MINSIZEREL QT_NO_DEBUG)
+            if (Qt5_POSITION_INDEPENDENT_CODE
+                    AND (CMAKE_VERSION VERSION_LESS 2.8.12
+                        AND (NOT CMAKE_CXX_COMPILER_ID STREQUAL \"GNU\"
+                        OR CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)))
+                set_property(TARGET ${_target} PROPERTY POSITION_INDEPENDENT_CODE ${Qt5_POSITION_INDEPENDENT_CODE})
+            endif()
         endforeach()
     endmacro()
 endif()

tests/auto/cmake/CMakeLists.txt

@@ -126,8 +126,11 @@ if (QT_WITH_ANGLE OR (NOT WIN32 AND NOT APPLE AND NOT NO_EGL))
 endif()
 expect_pass(test_opengl_lib)
 
-if (NOT CMAKE_VERSION VERSION_LESS 2.8.12)
+if (NOT CMAKE_VERSION VERSION_LESS 2.8.11)
     expect_pass(test_interface)
+endif()
+
+if (NOT CMAKE_VERSION VERSION_LESS 2.8.12)
     expect_pass(test_interface_link_libraries)
     expect_pass(test_moc_macro_target)
 endif()

tests/auto/cmake/test_interface/CMakeLists.txt

@@ -1,5 +1,5 @@
 
-cmake_minimum_required(VERSION 2.8.12)
+cmake_minimum_required(VERSION 2.8.11)
 
 project(test_interface)
 

tests/auto/cmake/test_use_modules_function/CMakeLists.txt

@@ -12,7 +12,5 @@ add_executable(three three.cpp)
 
 find_package(Qt5Core)
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${Qt5Core_EXECUTABLE_COMPILE_FLAGS}")
-
 qt5_use_modules(two Test)
 qt5_use_modules(three Gui Test)