Use GDB to examine Objective C class from crash (HandleDelegateSource bad access)

I am trying to debug an intermittent error on the iPhone, a crash with a trace that looks like:

objc_message_send
__invoking__
[NSInvocation invoke]
HandleDelegateSource
MainRunLoop
....

When GDB stops, I'd like to be able to determine details about what selector the system is attempting to be invoked - I've set a break point now around [NSInvocation Invoke], but from that point cannot figure out how to examine details of the NSInvocation object I am stopped in.

From stackoverflow

• If you look at the reference information for objc_msgSend you will see that the selector is the second argument. Now it should be easier to decipher the debugger output.

  objc_msgSend
  Sends a message with a simple return value to an instance of a class.
  id objc_msgSend(id theReceiver, SEL theSelector, ...)

  Parameters
  theReceiver
  A pointer that points to the instance of the class that is to receive the message.
  theSelector
  The selector of the method that handles the message.
  ...
  A variable argument list containing the arguments to the method.

• This article, recently published at Phrack should answer all your questions. Enlightening reading.

  Pestilence : lol +1 for linking to a relevant Phrack article

  Kendall Helmstetter Gelner : Good enough for me, and pretty much along the lines of what I was looking for. Thanks!

• A simple final answer - in GDB you can simply view the register with the name of the selector being called (theSelector parameter in lothar's answer). It's a C string, so you observe it using one of the following commands (depending on if you are running in the simulator or the device):

  Simulator: display /s $ecx
  Device: display /s $r1