How do I xcodebuild a static library with Bitcode enabled?

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Bitcode is a compile-time feature (not a link-time feature) which means that every .o file should contain an extra section called __bitcode when built with bitcode. You can confirm whether your binary is bitcode-compatible by running otool -l (my .o or .a file) | grep __LLVM.

When you build normally, Xcode adds the build flag -fembed-bitcode-marker to any clang invocation. This seems to be some sort of ‘this is where bitcode would go, if bitcode was enabled’ thing, and doesn’t actually enable bitcode.

When you “Build & Archive”, this flag is replaced by -fembed-bitcode, which really does build a Bitcode-enabled binary.

There seems to be two ways to make xcodebuild use -fembed-bitcode:

  • Use the ‘archive’ action, as in xcodebuild -target LookbackSDK archive instead of xcodebuild -target LookbackSDK build. This has the side-effect of putting binaries in your Xcode Organizer instead of the build/ folder, though you can work around that by using -exportArchive -archivePath ./build (thanks @JensAyton)
  • Force usage of the flag by adding Other C Flags with OTHER_CFLAGS="-fembed-bitcode". Your xcodebuild invocation would look something like xcodebuild OTHER_CFLAGS="-fembed-bitcode" -target LookbackSDK build.

The latter is what I chose so that I don’t have to change my build system, but it will generate warnings for every file, since now both -fembed-bitcode-marker and -fembed-bitcode are sent to clang. Luckilly the latter wins, generating a Bitcode-enabled library!

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