[CMake] Cross-compiling, CMAKE_C_FLAGS, and configure-time compiler tests
Justin Holewinski
justin.holewinski at gmail.com
Tue Dec 14 12:30:11 EST 2010
On Tue, Dec 14, 2010 at 4:45 AM, Johan Björk <phb at spotify.com> wrote:
> Hi Justin,
>
> I'm very unsure if this is the correct solution, but it worked for me. I
> haven't been able to find any good documentation stating how the CMakeCache
> interacts with other parts of CMake.
>
> My assumption is that since CMAKE_C{XX}_FLAGS is supposed to allow the user
> to set optional compilation flags, it prefers the value in the cache versus
> the one from the toolchain file.
>
> From one of my toolchain files, reproduce as necessary for CMAKE_C_FLAGS:
> SET(CMAKE_CXX_FLAGS "${CMAKE_C_FLAGS} -fno-rtti" CACHE STRING "" FORCE)
>
I'll have to give that a try. For now, I'm getting around the problem by
setting the flags within the parent CMakeLists.txt script after loading the
toolchain file.
I'm really not sure what the "best practice" is for this situation. The
compiler will work and can be tested without the "-arch" flags, but the
flags are necessary to build for the *right* architecture. Most
cross-compilers will only produce binaries for the target system, so the
point is moot. The iOS compilers, however, will generate code for Intel and
ARM so I'm not sure if testing the i386 back-end when I'm targeting ARM is
the right way or not.
>
> Cheers
> /Johan
>
>
> On Mon, Dec 13, 2010 at 4:49 PM, Justin Holewinski <
> justin.holewinski at gmail.com> wrote:
>
>> I am experiencing a cross-compiling issue that I believe is related to how
>> toolchain files interact with the configure-time compiler checks. For
>> reference, I am targeting the iOS 4.2 SDK. I have a toolchain file that
>> sets CMAKE_C_FLAGS, CMAKE_CXX_FLAGS, CMAKE_C_LINK_FLAGS, and
>> CMAKE_CXX_LINK_FLAGS with appropriate flags for the iOS platform, in
>> particular "-arch armv6 -arch armv7". The toolchain file also sets the
>> proper C and C++ compilers.
>>
>> When CMake is executed and the C compiler is tested, the
>> toolchain-specified compiler arguments are passed to the link line, but
>> *not* the compile line (according to the error output). Since the compile
>> line does not contain the "-arch" arguments, the generated object file is
>> for i386. However, since the link line contains these flags, the linker
>> tries to link ARM code and fails.
>>
>> Are there any additional variables I should be setting in addition to
>> CMAKE_C_FLAGS and CMAKE_CXX_FLAGS in order to get the compiler tests to use
>> the right flags? If I add the "-arch" flags using ADD_DEFINITIONS(), they
>> are passed to the compiler test and it succeeds. That seems like a hack and
>> not a proper solution, though.
>>
>> Below is the CMake output that prints the values of CMAKE_*_FLAGS as set
>> by the toolchain file, as well as the compile and link lines used by CMake.
>>
>> I am using CMake 2.8.3 on Snow Leopard 10.6.5.
>>
>> CMake Output:
>>
>> -- CMAKE_C_FLAGS: -arch armv6 -arch armv7 -pipe -no-cpp-precomp
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> -- CMAKE_CXX_FLAGS -arch armv6 -arch armv7 -pipe -no-cpp-precomp
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> -- CMAKE_C_LINK_FLAGS -arch armv6 -arch armv7 -pipe -no-cpp-precomp
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> -- CMAKE_CXX_LINK_FLAGS -arch armv6 -arch armv7 -pipe -no-cpp-precomp
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> -- CMAKE_C_FLAGS: -arch armv6 -arch armv7 -pipe -no-cpp-precomp
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> -- CMAKE_CXX_FLAGS -arch armv6 -arch armv7 -pipe -no-cpp-precomp
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> -- CMAKE_C_LINK_FLAGS -arch armv6 -arch armv7 -pipe -no-cpp-precomp
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> -- CMAKE_CXX_LINK_FLAGS -arch armv6 -arch armv7 -pipe -no-cpp-precomp
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> -- The C compiler identification is GNU
>> -- The CXX compiler identification is GNU
>> -- Check for working C compiler:
>> /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2
>> -- Check for working C compiler:
>> /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2 -- broken
>> CMake Error at
>> /opt/local/share/cmake-2.8/Modules/CMakeTestCCompiler.cmake:52 (MESSAGE):
>> The C compiler
>> "/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2" is
>> not
>> able to compile a simple test program.
>>
>> It fails with the following output:
>>
>> Change Dir:
>> /Users/jholewinski/projects/rapture/build-test/ios/CMakeFiles/CMakeTmp
>>
>>
>>
>> Run Build Command:/usr/bin/make "cmTryCompileExec/fast"
>>
>> /usr/bin/make -f CMakeFiles/cmTryCompileExec.dir/build.make
>> CMakeFiles/cmTryCompileExec.dir/build
>>
>> /opt/local/bin/cmake -E cmake_progress_report
>>
>> /Users/jholewinski/projects/rapture/build-test/ios/CMakeFiles/CMakeTmp/CMakeFiles
>> 1
>>
>> Building C object CMakeFiles/cmTryCompileExec.dir/testCCompiler.c.obj
>>
>> /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2
>>
>> -I/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk/usr/include
>> -o CMakeFiles/cmTryCompileExec.dir/testCCompiler.c.obj -c
>>
>> /Users/jholewinski/projects/rapture/build-test/ios/CMakeFiles/CMakeTmp/testCCompiler.c
>>
>>
>> Linking C executable cmTryCompileExec
>>
>> /opt/local/bin/cmake -E cmake_link_script
>> CMakeFiles/cmTryCompileExec.dir/link.txt --verbose=1
>>
>> /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2 -arch
>> armv6 -arch armv7 -pipe -no-cpp-precomp
>>
>> --sysroot=/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk
>> -miphoneos-version-min=4.2
>> CMakeFiles/cmTryCompileExec.dir/testCCompiler.c.obj -o cmTryCompileExec
>>
>> -L/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk/usr/lib
>>
>>
>> ld: warning: in CMakeFiles/cmTryCompileExec.dir/testCCompiler.c.obj,
>> file
>> was built for i386 which is not the architecture being linked (armv6)
>>
>> Undefined symbols for architecture armv6:
>>
>> "_main", referenced from:
>> start in crt1.3.1.o
>>
>> ld: symbol(s) not found for architecture armv6
>>
>> collect2: ld returned 1 exit status
>>
>> ld: warning: in CMakeFiles/cmTryCompileExec.dir/testCCompiler.c.obj,
>> file
>> was built for i386 which is not the architecture being linked (armv7)
>>
>> Undefined symbols for architecture armv7:
>>
>> "_main", referenced from:
>> start in crt1.3.1.o
>>
>> ld: symbol(s) not found for architecture armv7
>>
>> collect2: ld returned 1 exit status
>>
>> lipo: can't open input file:
>> /var/folders/pS/pSWOJvZ-FDS4A2Eo7TwIzE+++TI/-Tmp-//ccKkL4CZ.out (No such
>> file or directory)
>>
>> make[1]: *** [cmTryCompileExec] Error 1
>>
>> make: *** [cmTryCompileExec/fast] Error 2
>>
>>
>>
>>
>>
>> CMake will not be able to correctly generate this project.
>> Call Stack (most recent call first):
>> CMakeLists.txt:30 (project)
>>
>>
>> -- Configuring incomplete, errors occurred!
>>
>>
>> --
>>
>> Thanks,
>>
>> Justin Holewinski
>>
>>
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>
>
--
Thanks,
Justin Holewinski
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