[CMake] Cross-compiling, CMAKE_C_FLAGS, and configure-time compiler tests

[Justin Holewinski]

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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