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Xcode 5.1 Breaks Python Native Extensions and Ruby Gems

If you’ve installed Xcode 5.1 and want to install some of your favorite Python or Ruby toys on your OSX, you could have a bad surprise. For instance, if you try to install Fabric after upgrading to Xcode 5.1, you will fail!


pip install Fabric


creating build/temp.macosx-10.9-intel-2.7/src

cc -fno-strict-aliasing -fno-common -dynamic -arch x86_64 -arch i386 -pipe -fno-common -fno-strict-aliasing -fwrapv -mno-fused-madd -DENABLE_DTRACE -DMACOSX -Wall -Wstrict-prototypes -Wshorten-64-to-32 -fwrapv -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch x86_64 -arch i386 -pipe -std=c99 -O3 -fomit-frame-pointer -Isrc/ -I/usr/include/ -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c src/_fastmath.c -o build/temp.macosx-10.9-intel-2.7/src/_fastmath.o

clang: error: unknown argument: ’-mno-fused-madd’ [-Wunused-command-line-argument-hard-error-in-future]

clang: note: this will be a hard error (cannot be downgraded to a warning) in the future

error: command ’cc’ failed with exit status 1

The installation of Fabric failed because Fabric (probably PyCrypto) is using an unused command line (-mno-fused-madd), and, as of Xcode 5.1, clang treats unrecognized command-line options as errors.

Buried in the Xcode 5.1 release notes:


  • As of Apple LLVM compiler version 5.1 (clang-502) and later, the optimization level -O4 no longer implies link time optimization (LTO). In order to build with LTO explicitly use the -flto option in addition to the optimization level flag(15633276)

  • The Apple LLVM compiler in Xcode 5.1 treats unrecognized command-line options as errors. This issue has been seen when building both Python native extensions and Ruby Gems, where some invalid compiler options are currently specified.

Projects using invalid compiler options will need to be changed to remove those options. To help ease that transition, the compiler will temporarily accept an option to downgrade the error to a warning:


Note: This option will not be supported in the future.

To workaround this issue, set the ARCHFLAGS environment variable to downgrade the error to a warning. For example, you can install a Python native extension with:

$ ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future easy_install ExtensionName

Similarly, you can install a Ruby Gem with:

$ ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future gem install GemName

So if you want to install Fabric, you should type in a terminal:

export ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future
pip install Fabric

And everything will be fine…

Xcode, always a good surprise with every update….

From jc.

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