[CMake] Linking against OS X Frameworks

[Michael Wild]

On 9. Aug, 2009, at 23:09, Mike Jackson wrote:

> On Sun, Aug 9, 2009 at 3:07 PM, Michael Wild<themiwi at gmail.com> wrote:
>>
>> On 9. Aug, 2009, at 18:59, ML wrote:
>>
>>> Michael,
>>>
>>> Thank you for this example! It was really informative. Definitely a
>>> missing piece in my knowledge thus far.
>>>
>>> One question:
>>>
>>> I get an error stating:
>>>
>>> CMake Error at CMakeLists.txt:70 (message):
>>>  MoreFilesX requires the SDK version to be not newer than 10.4u  
>>> (10.6
>>>  detected)
>>>
>>> this comes from here:
>>>
>>>> # figure out Mac OSX SDK version (do not care for the u-suffix in  
>>>> 10.4u)
>>>> get_filename_component( SDK_VER ${CMAKE_OSX_SYSROOT} NAME )
>>>> string( REPLACE ".sdk" "" SDK_VER ${SDK_VER} )
>>>> string( REPLACE "MacOSX" "" SDK_VER ${SDK_VER} )
>>>> string( REGEX REPLACE "[a-zA-Z]" "" SDK_VER ${SDK_VER} )
>>>> # this REALLY needs the 10.4 SDK.
>>>> if( ${SDK_VER} VERSION_GREATER 10.4 )
>>>> message( SEND_ERROR "MoreFilesX requires the SDK version to be  
>>>> not newer
>>>> than 10.4u (${SDK_VER} detected)" )
>>>> endif( ${SDK_VER} VERSION_GREATER 10.4 )
>>>
>>> So how do I turn around and set 10.4u if it is not automatically  
>>> detected?
>>>
>>> It is like this:
>>>
>>> CMAKE_OSX_SYSROOT=/Developer/SDKs/MacOSX10.4u.sdk
>>>
>>> Best,
>>>
>>> -Jason
>>>
>>
>> CMake by default detects the most current SDK. If you want to use a
>> different one, you have to set it in the cache, by e.g. executing
>>
>> cmake -DCMAKE_OSX_SYSROOT=/Developer/SDKs/MacOSX10.4u.sdk
>> -DCMAKE_OSX_DEPLOYMENT_TARGET=10.4 .
>>
>> in the build tree. Above command also sets  
>> CMAKE_OSX_DEPLOYMENT_TARGET=10.4
>> for consistency.
>>
>> Please note that it is supported (and meaningful) to have different  
>> versions
>> of the SDK and the deployment target (both of them may be newer  
>> than the
>> other, so "all combinations allowed"). However, this has  
>> implications on
>> compiling, linking and loading, which I can't remember just off the  
>> top of
>> my head.
>>
>> Michael
>
> the CMAKE_OSX_DEPLOYMENT_TARGET setting controls the "Weak Linking"
> that OS  X does. It basically says what the minimum version of OS X
> your program can run on.
>
>
> the CMAKE_OSX_SYSROOT setting controls the "maximum" version of OS X
> that your program can run on. By setting BOTH to 10.4 you are
> basically saying that your program can run ONLY on OS X 10.4. Is that
> what you want?
>
> If you link against a library that has a function in 10.5 that is not
> in 10.4 then your program will likely crash. It is up to you to take
> the necessary steps in your code to ensure this does not happen, maybe
> by using an alternate function?
>
> If you read bug number 6195 you will get all the detailed explanations
> you need plus all the history that will allow you to make an informed
> decision about how to set those values:
>
> http://public.kitware.com/Bug/view.php?id=6195
>
> Mike

According to this document http://developer.apple.com/documentation/DeveloperTools/Conceptual/cross_development/Configuring/configuring.html

your information is partially wrong: CMAKE_OSX_SYSROOT gives you the  
maximum SDK version from which you can USE features at built time. All  
newer features will not be available. It doesn't say anything about  
run time.

CMAKE_OSX_DEPLOYMENT_TARGET, on the other hand, gives the minimum  
version required to run the application. All the symbols that fall in  
between these two versions (where CMAKE_OSX_DEPLOYMENT_TARGET has to  
be lower or equal to CMAKE_OSX_SYSROOT) are weakly linked, meaning  
their address is set to NULL and need to be tested at runtime whether  
they are available (described here http://developer.apple.com/documentation/DeveloperTools/Conceptual/cross_development/Using/using.html#/ 
/apple_ref/doc/uid/20002000-1114537-BABHHJBC and here http://developer.apple.com/technotes/tn2002/tn2064.html)