Dealing with Xcode 9 + macOS <= 10.12 and missing functions

[Joshua Root]

On 2017-9-29 18:48 , Leonardo Brondani Schenkel wrote:
> On 2017-09-29 10:23, Joshua Root wrote:
>> On 2017-9-29 18:14 , Leonardo Brondani Schenkel wrote:
>>> This seems to be an issue in XCode 9 to me, since I believe that when 
>>> setting the deployment target to 10.12 or earlier it should not be 
>>> exposing symbols that are not available at runtime.
>>
>> It is working correctly as far as it goes; autoconf just doesn't solve 
>> the entire problem. Symbols that are not available on all the OS 
>> versions being targeted must be checked for at runtime before use. 
>> That way a single binary can use newer APIs when they are available 
>> but still run on older OS releases.
> 
> Fair enough. I think I don't fully understand the role of "deployment 
> target": to me it was the *maximum* version I want to be able to link 
> against, but apparently it is the opposite.

The SDK you build against determines the latest APIs that can be used 
(MAC_OS_X_VERSION_MAX_ALLOWED) while MACOSX_DEPLOYMENT_TARGET (which 
affects MAC_OS_X_VERSION_MIN_REQUIRED) determines the oldest OS on which 
the binary can run.

That means, symbols available on MAC_OS_X_VERSION_MIN_REQUIRED are 
linked normally, while symbols that are available on 
MAC_OS_X_VERSION_MAX_ALLOWED but not MAC_OS_X_VERSION_MIN_REQUIRED are 
weak linked, and trying to use symbols that are not available on 
MAC_OS_X_VERSION_MAX_ALLOWED results in a link error.

> However, the motivation for my the original post was more to talk about 
> if it makes sense to have something done on MacPorts level to mitigate 
> this issue or just deal with it on a port-by-port basis. Just to be 
> clear: I'm not advocating one or the other — I'm just curious about what 
> the lists thinks.

Well, our installation instructions say to install the Command Line 
Tools, which avoids this problem. I guess we could try setting 
MAC_OS_X_VERSION_MAX_ALLOWED explicitly, but unlike 
MACOSX_DEPLOYMENT_TARGET, it isn't picked up from the environment by the 
compiler driver, so a lot of ports would require special handling to get 
it into the CPPFLAGS.

- Josh