FBSDKLoginManager: undefined symbols for architecture x86_64 + linker command failed with exit code 1

I just upgraded Facebook iOS SDK to v.4.0.1 and I got these errors:

Undefined symbols for architecture x86_64:
  "_OBJC_CLASS_$_FBSDKLoginManager", referenced from:
      objc-class-ref in Controller1.o
      objc-class-ref in AppDelegate.o
      objc-class-ref in Controller2.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I already tried to change linkers: with -all_load I get the same error, while with -force_load it becomes "ld: file not found: -fobjc-arc". Any solutions?

I ran into the same problem. If you're adding Facebook Login to your app (which I presume you are) you also need to drag the FBSDKLoginKit.framework file into your Xcode project in addition to the FBSDKCoreKit.framework file.

The current instructions on Facebook's SDK Getting Started page forget to mention this. In version < 4 of the SDK, there was just one file to drag in to your project.