CMake croscompile problem with CXX_FLAGS in linker

Question

I have following toolchain for iPhone crosscompilation on mac os x:

# Platform Info
SET (CMAKE_SYSTEM_VERSION 1)
SET (CMAKE_SYSTEM_PROCESSOR arm)

# SDK Info
SET (SDKVER "3.0")
SET (DEVROOT "/Developer/Platforms/iPhoneOS.platform/Developer")
SET (SDKROOT "${DEVROOT}/SDKs/iPhoneOS${SDKVER}.sdk")
SET (CMAKE_OSX_SYSROOT "${SDKROOT}")
SET (CMAKE_OSX_ARCHITECTURES "armv6")
SET_PROPERTY(GLOBAL PROPERTY TARGET_SUPPORTS_SHARED_LIBS TRUE)

# C Compiler
SET (CMAKE_C_COMPILER "${DEVROOT}/usr/bin/arm-apple-darwin9-gcc-4.2.1")
#SET (LINK_FLAGS "-arch armv6 -arch armv7")
#SET (CMAKE_C_LINK_EXECUTABLE "${DEVROOT}/usr/bin/g++-4.2")
SET (CMAKE_C_FLAGS "-x objective-c")
SET (CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS} -DDEBUG=1 -ggdb")
SET (CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS} -DNDEBUG=1")
SET (CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS} -DNDEBUG=1 -ggdb")

# CXX Compiler
SET (CMAKE_CXX_COMPILER "${DEVROOT}/usr/bin/arm-apple-darwin9-g++-4.2.1")
SET (CMAKE_CXX_FLAGS "-x objective-c++")
SET (CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS} -DDEBUG=1 -ggdb")
SET (CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS} -DNDEBUG=1")
SET (CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS} -DNDEBUG=1 -ggdb")

# Definitions
#ADD_DEFINITIONS("-arch armv6")
#ADD_DEFINITIONS("-arch armv7")
ADD_DEFINITIONS("-pipe")
ADD_DEFINITIONS("-no-cpp-precomp")
ADD_DEFINITIONS("--sysroot=${SDKROOT}")
ADD_DEFINITIONS("-miphoneos-version-min=${SDKVER}")

# System Includes
INCLUDE_DIRECTORIES(SYSTEM "${SDKROOT}/usr/include")
INCLUDE_DIRECTORIES(SYSTEM "${SDKROOT}/usr/include/c++/4.2.1")
INCLUDE_DIRECTORIES(SYSTEM "${SDKROOT}/usr/include/c++/4.2.1/armv6-apple-darwin9")
INCLUDE_DIRECTORIES(SYSTEM "${SDKROOT}/opt/iphone-${SDKVER}/include")
INCLUDE_DIRECTORIES(SYSTEM "${SDKROOT}/usr/local/iphone-${SDKVER}/include")

# System Libraries
LINK_DIRECTORIES("${SDKROOT}/usr/lib")
LINK_DIRECTORIES("${SDKROOT}/usr/lib/gcc/arm-apple-darwin9/4.2.1/")
#LINK_DIRECTORIES("${SDKROOT}/opt/iphone-${SDKVER}/lib")
#LINK_DIRECTORIES("${SDKROOT}/usr/local/iphone-${SDKVER}/lib")

# Root Paths
SET (CMAKE_FIND_ROOT_PATH "${SDKROOT}" "/opt/iphone-${SDKVER}/" "/usr/local/iphone-${SDKVER}/")
SET (CMAKE_FIND_ROOT_PATH_MODE_PROGRAM BOTH)
SET (CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
SET (CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

# CMake Parameters
SET (iPhone 1)
SET (iPhoneOS 1)
SET (iPhoneOS_VERSION ${SDKVER})
SET (CMAKE_CROSSCOMPILING 1)

#SET_TARGET_PROPERTIES(p3dm PROPERTIES LINK_FLAGS "-arch armv6 -arch armv7")

# HELPERS
#---------

MACRO(ADD_FRAMEWORK appname fwname)
    find_library(FRAMEWORK_${fwname}
        NAMES ${fwname}
        PATHS ${SDKROOT}/System/Library
        PATH_SUFFIXES Frameworks
        NO_DEFAULT_PATH)
    if( ${FRAMEWORK_${fwname}} STREQUAL FRAMEWORK_${fwname}-NOTFOUND)
        MESSAGE(ERROR ": Framework ${fwname} not found")
    else()
        TARGET_LINK_LIBRARIES(${appname} ${FRAMEWORK_${fwname}})
        MESSAGE(STATUS "Framework ${fwname} found at ${FRAMEWORK_${fwname}}")
    endif()
endmacro(ADD_FRAMEWORK)

And i use following CMakeLists.txt:

# PROJECT PARAMETERS
#--------------------

SET(APP_NAME p3dm)
PROJECT(${APP_NAME})

# SOURCE CODE
#-------------

SET(CMAKE_CXX_FLAGS "-x objective-c++")

INCLUDE_DIRECTORIES(SYSTEM ../inc/ ../xsrc/)

FILE(GLOB headers ../src/*.h ../xsrc/*.h)
FILE(GLOB sources ../src/*.cpp ../xsrc/*.c ../xsrc/*.cpp)

#set_source_files_properties(${sources} PROPERTIES LANGUAGE C )

# EXECUTABLE
#------------

SET(MACOSX_BUNDLE_GUI_IDENTIFIER "org.reversity.${APPNAME}")
SET(APP_TYPE MACOSX_BUNDLE)

ADD_EXECUTABLE(${APP_NAME} ${APP_TYPE} ${headers} ${sources})

SET_TARGET_PROPERTIES(${APP_NAME} PROPERTIES XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY "iPhone Developer: Mario Hros")

# FRAMEWORKS
#------------

ADD_FRAMEWORK(${APP_NAME} UIKit)

I use following compilation bash script:

#!/bin/bash

unset CPATH
unset C_INCLUDE_PATH
unset CPLUS_INCLUDE_PATH
unset OBJC_INCLUDE_PATH
unset LIBS
unset DYLD_FALLBACK_LIBRARY_PATH
unset DYLD_FALLBACK_FRAMEWORK_PATH

export SDKVER="3.0"
export DEVROOT="/Developer/Platforms/iPhoneOS.platform/Developer"
export SDKROOT="$DEVROOT/SDKs/iPhoneOS$SDKVER.sdk"
export PKG_CONFIG_PATH="$SDROOT/usr/lib/pkgconfig":"/opt/iphone-$SDKVER/lib/pkgconfig":"/usr/local/iphone-$SDKVER/lib/pkgconfig"
export PKG_CONFIG_LIBDIR="$PKG_CONFIG_PATH"
export MAINFOLDER=`pwd`

cmake . \
                         -DCMAKE_TOOLCHAIN_FILE="$MAINFOLDER/cmake/iphone-$SDKVER.toolchain" \
                         -DCMAKE_INSTALL_PREFIX="/opt/iphone-$SDKVER" \
                         "$@"

The problem is, that it uses CMAKE_CXX_FLAGS also in linker. Compilation is fine. Linking looks fine, it adds correct -framework flags, but also adds CMAKE_CXX_FLAGS (which are -x objective-c++) so instead of linking object files compiled previously it behaves like compiling objective c++ (-x objective-c++) and it is impossible to link these objects.

I am getting errors like

ComponentManager.cpp.o:20: error: stray '\341' in program

Don't you know what I am doing wrong?

Answer 1

You can set the LINKER_LANGUAGE to C to force CMake to use the CMAKE_C_FLAGS for the linker. Check it out here.

Answer 2

I've solved this problem by removing CMAKE_CXX_FLAGS and CMAKE_C_FLAGS from the toolchain file and adding ADD_DEFINITIONS("-x objective-c++") to CMakeLists.txt.

That way -x objective-c++ flags get passed only to the compiler (not linker) and only for my source code (not cmake test compilation which happens before building my target).