CMake: rework compilation/link flags

- Default compiler and linker flags were added silently. They are now
  set in the cache if no previous values are present.
- Debug flags and regular flags have been merged.
- Position-independent code (doesn't appear in the cache because CMake
  lacks variables like CMAKE_EXE_COMPILE_FLAGS):
  - Shared libraries are compiled with -fPIC.
  - Executables and static libraries are compiled with -fPIE.
  - Executables are linked with -pie -fPIE.

CMakeLists.txt

@@ -58,9 +58,40 @@ endif()
 
 ### Flags ###
 
-set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -Wall -Wextra -Wstrict-prototypes")
-set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -Wall -Wextra")
-set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,--no-undefined")
+# Specific compiler flags
+# These variables are to be used (manually) when compiling a shared
+# library or an executable (or static library).
+set(SHARED_FLAGS "-fPIC")
+set(EXE_FLAGS "-fPIE")
+
+# Common compiler flags
+set(C_CXX_COMMON_FLAGS "-Wall -Wextra")
+set(C_FLAGS "${C_CXX_COMMON_FLAGS} -Wstrict-prototypes")
+set(CXX_FLAGS "${C_CXX_COMMON_FLAGS}")
+
+if (NOT CMAKE_C_FLAGS)
+  set(CMAKE_C_FLAGS ${C_FLAGS}
+    CACHE STRING "Set default C flags" FORCE)
+endif()
+
+if (NOT CMAKE_CXX_FLAGS)
+  set(CMAKE_CXX_FLAGS ${CXX_FLAGS}
+    CACHE STRING "Set default C++ flags" FORCE)
+endif()
+
+# Linker flags
+# Question: why the hell does CMAKE_SHARED_LINKER_FLAGS contain " "
+#           by default?!
+if ("${CMAKE_SHARED_LINKER_FLAGS}" STREQUAL " ")
+  set(CMAKE_SHARED_LINKER_FLAGS "-Wl,--no-undefined"
+    CACHE STRING "Set default shared linker flags" FORCE)
+endif()
+
+# Linker flags when linking an executable
+if ("${CMAKE_EXE_LINKER_FLAGS}" STREQUAL " ")
+  set(CMAKE_EXE_LINKER_FLAGS "-pie -fPIE"
+    CACHE STRING "Set default shared linker flags" FORCE)
+endif()
 
 
 ### Libraries ###

libowlps-client/CMakeLists.txt

@@ -1,17 +1,30 @@
 # Explicitly link to libc
 set(EXTRA_LIBS ${EXTRA_LIBS} c)
 
-add_library(libowlps-client.a STATIC libowlps-client.c)
+# Targets
 add_library(libowlps-client.so SHARED libowlps-client.c)
+add_library(libowlps-client.a STATIC libowlps-client.c)
+
+# Fix targets' names
 set_target_properties(
-  libowlps-client.a libowlps-client.so
+  libowlps-client.so libowlps-client.a
   PROPERTIES
   OUTPUT_NAME owlps-client
   SOVERSION 1
   VERSION 1.0
   )
+
+# Add compile flags
+set_target_properties(libowlps-client.so
+  PROPERTIES COMPILE_FLAGS ${SHARED_FLAGS})
+set_target_properties(libowlps-client.a
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})
+
+# Link libraries
 target_link_libraries(libowlps-client.so libowlps.so ${EXTRA_LIBS})
 target_link_libraries(libowlps-client.a libowlps.a ${EXTRA_LIBS})
+
+# Install targets
 install(
   TARGETS libowlps-client.so libowlps-client.a
   DESTINATION lib)

libowlps-resultreader/CMakeLists.txt

@@ -1,8 +1,11 @@
 # Explicitly link to libc
 set(EXTRA_LIBS ${EXTRA_LIBS} c)
 
+# Targets
 add_library(libowlps-resultreader.a STATIC libowlps-resultreader.c)
 add_library(libowlps-resultreader.so SHARED libowlps-resultreader.c)
+
+# Fix targets' names
 set_target_properties(
   libowlps-resultreader.a libowlps-resultreader.so
   PROPERTIES
@@ -10,11 +13,28 @@ set_target_properties(
   SOVERSION 1
   VERSION 1.0
   )
+
+# Add compile flags
+set_target_properties(libowlps-resultreader.so
+  PROPERTIES COMPILE_FLAGS ${SHARED_FLAGS})
+set_target_properties(libowlps-resultreader.a
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})
+
+# Link libraries
 target_link_libraries(libowlps-resultreader.so libowlps.so ${EXTRA_LIBS})
 target_link_libraries(libowlps-resultreader.a libowlps.a ${EXTRA_LIBS})
+
+# Install targets
 install(
   TARGETS libowlps-resultreader.so libowlps-resultreader.a
   DESTINATION lib)
+install(
+  FILES owlps-resultreader.h
+  DESTINATION include)
+
+
+
+### Demo program ###
 
 add_executable(owlps-resultreader-udp owlps-resultreader-udp.c)
 target_link_libraries(owlps-resultreader-udp
@@ -23,12 +43,6 @@ target_link_libraries(owlps-resultreader-udp
 install(
   TARGETS owlps-resultreader-udp
   DESTINATION bin)
-install(
-  FILES owlps-resultreader.h
-  DESTINATION include)
-
-
-### Demo program ###
 
 add_executable(owlps-resultreader-udp.semistatic EXCLUDE_FROM_ALL
   owlps-resultreader-udp.c)
@@ -49,3 +63,10 @@ target_link_libraries(owlps-resultreader-udp.static
 # Add the static target to the global list of static targets
 list(APPEND OWLPS_STATIC_TARGETS owlps-resultreader-udp.static)
 set(OWLPS_STATIC_TARGETS ${OWLPS_STATIC_TARGETS} PARENT_SCOPE)
+
+# Add compile flags for the above targets
+set_target_properties(
+  owlps-resultreader-udp
+  owlps-resultreader-udp.semistatic
+  owlps-resultreader-udp.static
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})

libowlps/CMakeLists.txt

@@ -8,8 +8,11 @@ endif()
 # Explicitly link to libc
 set(EXTRA_LIBS ${EXTRA_LIBS} c)
 
-add_library(libowlps.a STATIC libowlps.c)
+# Targets
 add_library(libowlps.so SHARED libowlps.c)
+add_library(libowlps.a STATIC libowlps.c)
+
+# Fix targets' names
 set_target_properties(
   libowlps.a libowlps.so
   PROPERTIES
@@ -17,8 +20,18 @@ set_target_properties(
   SOVERSION 3
   VERSION 3.1
   )
+
+# Add compile flags
+set_target_properties(libowlps.so
+  PROPERTIES COMPILE_FLAGS ${SHARED_FLAGS})
+set_target_properties(libowlps.a
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})
+
+# Link libraries
 target_link_libraries(libowlps.so ${EXTRA_LIBS})
 target_link_libraries(libowlps.a ${EXTRA_LIBS})
+
+# Install targets
 install(
   TARGETS libowlps.so libowlps.a
   DESTINATION lib)

owlps-aggregator/CMakeLists.txt

@@ -27,3 +27,10 @@ target_link_libraries(owlps-aggregatord.static
 # Add the static target to the global list of static targets
 list(APPEND OWLPS_STATIC_TARGETS owlps-aggregatord.static)
 set(OWLPS_STATIC_TARGETS ${OWLPS_STATIC_TARGETS} PARENT_SCOPE)
+
+# Add compile flags for the above targets
+set_target_properties(
+  owlps-aggregatord
+  owlps-aggregatord.semistatic
+  owlps-aggregatord.static
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})

owlps-client/CMakeLists.txt

@@ -50,3 +50,10 @@ endif()
 # Add the static target to the global list of static targets
 list(APPEND OWLPS_STATIC_TARGETS owlps-client.static)
 set(OWLPS_STATIC_TARGETS ${OWLPS_STATIC_TARGETS} PARENT_SCOPE)
+
+# Add compile flags for the above targets
+set_target_properties(
+  owlps-client
+  owlps-client.semistatic
+  owlps-client.static
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})

owlps-listener/CMakeLists.txt

@@ -62,3 +62,10 @@ target_link_libraries(owlps-listenerd.static
 # Add the static target to the global list of static targets
 list(APPEND OWLPS_STATIC_TARGETS owlps-listenerd.static)
 set(OWLPS_STATIC_TARGETS ${OWLPS_STATIC_TARGETS} PARENT_SCOPE)
+
+# Add compile flags for the above targets
+set_target_properties(
+  owlps-listenerd
+  owlps-listenerd.semistatic
+  owlps-listenerd.static
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})

owlps-positioner/CMakeLists.txt

@@ -91,6 +91,13 @@ target_link_libraries(owlps-positionerd.static
 list(APPEND OWLPS_STATIC_TARGETS owlps-positionerd.static)
 set(OWLPS_STATIC_TARGETS ${OWLPS_STATIC_TARGETS} PARENT_SCOPE)
 
+# Add compile flags for the above targets
+set_target_properties(
+  owlps-positionerd
+  owlps-positionerd.semistatic
+  owlps-positionerd.static
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})
+
 
 ### Extra targets ###
 

owlps-udp-to-http/CMakeLists.txt

@@ -30,3 +30,10 @@ target_link_libraries(owlps-udp-to-http.static
 # Add the static target to the global list of static targets
 list(APPEND OWLPS_STATIC_TARGETS owlps-udp-to-http.static)
 set(OWLPS_STATIC_TARGETS ${OWLPS_STATIC_TARGETS} PARENT_SCOPE)
+
+# Add compile flags for the above targets
+set_target_properties(
+  owlps-udp-to-http
+  owlps-udp-to-http.semistatic
+  owlps-udp-to-http.static
+  PROPERTIES COMPILE_FLAGS ${EXE_FLAGS})