Refactor generation of shared library flags

CMAKE_SHARED_LIBRARY_<lang>_FLAGS has flags on various platforms for a
variety of purposes that are correlated with shared libraries but not
exclusive to them.  Refactor generation of these flags to use new
purpose-specific platform variables

  CMAKE_<lang>_COMPILE_OPTIONS_DLL
  CMAKE_<lang>_COMPILE_OPTIONS_PIC
  CMAKE_<lang>_COMPILE_OPTIONS_PIE

Activate the DLL flags specifically for shared libraries.  Add a new
POSITION_INDEPENDENT_CODE target property to activate PIC/PIE flags, and
default to true for shared libraries to preserve default behavior.
Initialize the new property from CMAKE_POSITION_INDEPENDENT_CODE to
allow easy global configuration in projects.

Although the default behavior is unchanged by this refactoring, the new
approach ignores CMAKE_SHARED_LIBRARY_<lang>_FLAGS completely.  We must
leave it set in case projects reference the value.  Furthermore, if a
project modifies CMAKE_SHARED_LIBRARY_<lang>_FLAGS it expects the new
value to be used.  Add policy CMP0018 to handle compatibility with
projects that modify this platform variable.

Add a PositionIndependentCode test on platforms where we can get
meaningful results.

7 files changed, 108 insertions, 0 deletions

diff --git a/Tests/PositionIndependentTargets/CMakeLists.txt b/Tests/PositionIndependentTargets/CMakeLists.txt
new file mode 100644
index 0000000..eec893d
--- /dev/null
+++ b/Tests/PositionIndependentTargets/CMakeLists.txt
@@ -0,0 +1,13 @@
+
+cmake_minimum_required(VERSION 2.8)
+
+project(PositionIndependentTargets)
+
+include(CheckCXXSourceCompiles)
+
+include_directories("${CMAKE_CURRENT_SOURCE_DIR}") # For pic_test.h
+
+add_subdirectory(global)
+add_subdirectory(targets)
+
+add_executable(PositionIndependentTargets main.cpp)
diff --git a/Tests/PositionIndependentTargets/global/CMakeLists.txt b/Tests/PositionIndependentTargets/global/CMakeLists.txt
new file mode 100644
index 0000000..1d662f8
--- /dev/null
+++ b/Tests/PositionIndependentTargets/global/CMakeLists.txt
@@ -0,0 +1,37 @@
+
+set(CMAKE_POSITION_INDEPENDENT_CODE True)
+
+add_executable(test_target_executable_global
+  "${CMAKE_CURRENT_SOURCE_DIR}/../pic_main.cpp"
+)
+
+add_library(test_target_shared_library_global
+  SHARED "${CMAKE_CURRENT_SOURCE_DIR}/../pic_lib.cpp"
+)
+set_target_properties(test_target_shared_library_global
+  PROPERTIES DEFINE_SYMBOL PIC_TEST_BUILD_DLL
+)
+
+add_library(test_target_static_library_global
+  STATIC "${CMAKE_CURRENT_SOURCE_DIR}/../pic_lib.cpp"
+)
+set_target_properties(test_target_static_library_global
+  PROPERTIES COMPILE_DEFINITIONS PIC_TEST_STATIC_BUILD
+)
+
+
+file(READ
+  "${CMAKE_CURRENT_SOURCE_DIR}/../pic_test.h"
+  PIC_HEADER_CONTENT
+)
+
+check_cxx_source_compiles(
+  "
+${PIC_HEADER_CONTENT}
+int main(int,char**) { return 0; }\n"
+  PIC_TRY_COMPILE_RESULT
+)
+
+if (NOT PIC_TRY_COMPILE_RESULT)
+  message(SEND_ERROR "TRY_COMPILE with content requiring __PIC__ failed. ${OUTPUT}")
+endif()
diff --git a/Tests/PositionIndependentTargets/main.cpp b/Tests/PositionIndependentTargets/main.cpp
new file mode 100644
index 0000000..e72cef7
--- /dev/null
+++ b/Tests/PositionIndependentTargets/main.cpp
@@ -0,0 +1,2 @@
+
+int main(int,char**) { return 0; }
diff --git a/Tests/PositionIndependentTargets/pic_lib.cpp b/Tests/PositionIndependentTargets/pic_lib.cpp
new file mode 100644
index 0000000..b8b25a3
--- /dev/null
+++ b/Tests/PositionIndependentTargets/pic_lib.cpp
@@ -0,0 +1,12 @@
+
+#include "pic_test.h"
+
+class PIC_TEST_EXPORT Dummy
+{
+  int dummy();
+};
+
+int Dummy::dummy()
+{
+  return 0;
+}
diff --git a/Tests/PositionIndependentTargets/pic_main.cpp b/Tests/PositionIndependentTargets/pic_main.cpp
new file mode 100644
index 0000000..6a41a7a
--- /dev/null
+++ b/Tests/PositionIndependentTargets/pic_main.cpp
@@ -0,0 +1,4 @@
+
+#include "pic_test.h"
+
+int main(int,char**) { return 0; }
diff --git a/Tests/PositionIndependentTargets/pic_test.h b/Tests/PositionIndependentTargets/pic_test.h
new file mode 100644
index 0000000..3f64557
--- /dev/null
+++ b/Tests/PositionIndependentTargets/pic_test.h
@@ -0,0 +1,20 @@
+
+#if defined(__ELF__)
+#  if !defined(__PIC__)
+#    error "The POSITION_INDEPENDENT_CODE property should cause __PIC__ to be defined on ELF platforms."
+#  endif
+#endif
+
+#if defined(PIC_TEST_STATIC_BUILD)
+#  define PIC_TEST_EXPORT
+#else
+#  if defined(_WIN32) || defined(WIN32) /* Win32 version */
+#    ifdef PIC_TEST_BUILD_DLL
+#      define PIC_TEST_EXPORT __declspec(dllexport)
+#    else
+#      define PIC_TEST_EXPORT __declspec(dllimport)
+#    endif
+#  else
+#    define PIC_TEST_EXPORT
+#  endif
+#endif
diff --git a/Tests/PositionIndependentTargets/targets/CMakeLists.txt b/Tests/PositionIndependentTargets/targets/CMakeLists.txt
new file mode 100644
index 0000000..4724c85
--- /dev/null
+++ b/Tests/PositionIndependentTargets/targets/CMakeLists.txt
@@ -0,0 +1,20 @@
+
+add_executable(test_target_executable_properties "${CMAKE_CURRENT_SOURCE_DIR}/../pic_main.cpp")
+set_target_properties(test_target_executable_properties
+  PROPERTIES
+    POSITION_INDEPENDENT_CODE True
+)
+
+add_library(test_target_shared_library_properties SHARED "${CMAKE_CURRENT_SOURCE_DIR}/../pic_lib.cpp")
+set_target_properties(test_target_shared_library_properties
+  PROPERTIES
+    POSITION_INDEPENDENT_CODE True
+    DEFINE_SYMBOL PIC_TEST_BUILD_DLL
+)
+
+add_library(test_target_static_library_properties STATIC "${CMAKE_CURRENT_SOURCE_DIR}/../pic_lib.cpp")
+set_target_properties(test_target_static_library_properties
+  PROPERTIES
+    POSITION_INDEPENDENT_CODE True
+    COMPILE_DEFINITIONS PIC_TEST_STATIC_BUILD
+)