问题:

In the scheme run debugger popup, all it shows is 'None' and 'GDB'. This is for an iPad 4.2 simulator built with LLVM.

回答1:

You can't. In words of an Apple employee, LLDB is not available for iOS development yet. As of july 2011 it is unknown when LLDB will become available for iOS.

In Xcode 4.0.2 your only option is GDB. In Xcode 4.2 you have LLDB as an option, but you can't use it:

The LLDB project doesn't list a date for iOS support. The FAQ says:

Q: What targets does LLDB currently support?
Mac OS X native debugging for i386 and x86_64 targets.

And the WWDC 2011 sessions that talk about LLDB (eg: 321 Migrating to LLDB) don't mention anything about iOS devices.

回答2:

LLDB is shipping with XCode 4.0.1 that you can buy from Apple's AppStore.

You only have to switch to LLDB. You can do that by pressing Option key when clicking on "Run" and choose LLDB instead of CDB (third drop down box on Info tab).

Here's XCode (can be found in "About XCode) that I have:

Version:    4.0 (4A1006)
  Location: /Developer
  Applications:
  Xcode:    4.0.1 (99)
  Instruments:  4.0 (3538)
  Dashcode: 3.0.2 (333)
  SDKs:
  Mac OS X:
  10.6: (4A1006)
  iPhone OS:
  3.2:  (7B500)
  4.3:  (8F191m)
  iPhone Simulator:
  3.2:  (7W367a)
  4.0:  (8A400)
  4.1:  (8B117)
  4.2:  (8C134)
  4.3:  (8F192)