[cmake-developers] Unsupported "-arch x86_64" mysteriously ends up in Fortran_FLAGS

[Mojca Miklavec]

On Wed, Jan 23, 2013 at 5:29 PM, Brad King wrote:
> On 01/22/2013 02:11 PM, Mojca Miklavec wrote:
>> I realised that an unsupported compiler flag "-arch x86_64"
>> mysteriously sneaks into Fortran_FLAGS when
>>     -DCMAKE_OSX_ARCHITECTURES="x86_64"
>
> The "-arch" flag is hard-coded here:
>
>  http://cmake.org/gitweb?p=cmake.git;a=blob;f=Source/cmLocalGenerator.cxx;hb=v2.8.10.2#l1826
>
> It was added to CMake way back when universal binary support was
> first added to OS X under the assumption that all compilers that
> would be used in combination with CMAKE_OSX_ARCHITECTURES would
> support the flag.  Obviously the assumption is wrong.

True. Not even the original gcc compilers (without Apple's
modifications) support the "-arch" flag. MacPorts ship the original
gcc compilers and actually use them for a couple of ports. I'm not
100% sure, but some of the reasons include faster and more efficient
computations in physics simulations (apparently using the latest gcc
4.8 matters) or support for Fortran. So testing for Mac OS X and GCC
doesn't yet guarantee the existence of that flag.

> The hard-coded flag needs to be replaced with a lookup of a new
> per-language platform information variable, perhaps called
>
>  CMAKE_<LANG>_OSX_ARCHITECTURE_FLAG

Thanks a lot for the answer.

Since you know the internals much better than I do: do I have to file
a bug report myself?

Thanks again,
    Mojca