Comments on: SDKs and Deployment Targets

By: links for 2009-11-02 « Amy G. Dala

links for 2009-11-02 « Amy G. Dala — Mon, 02 Nov 2009 14:02:15 +0000

[...] Clarkcox.com » Blog Archive » SDKs and Deployment Targets (tags: iphone development reference) [...]

By: Benjohn

Benjohn — Wed, 22 Jul 2009 11:38:04 +0000

Thanks for this brilliantly useful info, I think my users are likely to appreciate it too. Some additional magic sauce that I’ve just found is that you need to weakly link in the “base sdk” frameworks that may not exist on the “deployment platform”. You can read how to do that here: http://blog.dearprakash.com/2009/06/20/iprogrammer-tip-6-weak-linking-additional-libraries/

Thanks again! – Benjohn

By: Emanuele Vulcano

Emanuele Vulcano — Thu, 02 Jul 2009 13:04:17 +0000

The correct way to prevent a compiler from optimizing away, anyway, is to use volatile. Otherwise, a cunning compiler may infer (and is allowed to) optimize away the use of fn.

By: Chris Hanson

Chris Hanson — Wed, 01 Jul 2009 19:10:51 +0000

@Chris Suter: The compiler should only emit a warning for that if the declaration of APIForAmazingNewFeature isn’t tagged with `__attribute__((weak_import))`, which is what indicates to the compiler that it can be NULL; otherwise, assuming that functions aren’t NULL is a valid optimization.

This attribute (and `__attribute__((unavailable))` of course) are what the macros in AvailabilityMacros.h (old) and Availability.h (new) are for; they’re set up to tag declarations with the appropriate attributes based on the combination of minimum required (deployment target) and maximum allowed (SDK) OS that you’ve chosen.

By: Chris Ryland

Chris Ryland — Thu, 25 Jun 2009 18:40:54 +0000

@Chris Suter: Yes, but the new static analysis clang-based engine Xcode 3.2 would probably see those two as identical, and still give you a warning. I wonder if there’s a better way.

By: Cédric Luthi

Cédric Luthi — Thu, 25 Jun 2009 14:51:02 +0000

Also good to know: the SDKROOT setting translates to gcc’s -isysroot option, MACOSX_DEPLOYMENT_TARGET to -mmacosx-version-min and IPHONEOS_DEPLOYMENT_TARGET to -miphoneos-version-min.

By: Chris Suter

Chris Suter — Wed, 24 Jun 2009 00:31:27 +0000

One of the newer compilers (probably clang, but possible gcc-llvm—I forget), spews a warning when you do:

if(APIForAmazingNewFeature != NULL) {

The warning complains that the test is always TRUE, which suggests, although I haven’t checked, that it’s getting optimised away.

The warning appears to go away if you do:

fn = APIForAmazingNewFeature;
if (fn) {
// Do amazing stuff
}