Question

I want to be able to specify a subset of all C++ exceptions for Xcode (lldb) to break upon. It looks like this is supported in the UI:

But for the life of me, I can’t make it work. If I leave it set to the default “All C++ Exceptions”, it works and every exception thrown triggers the breakpoint. If I attempt to specify an exception by name, the breakpoint is never triggered.

Has anyone else had issues with this, or is this just my problem?

Answer 1

Despite the UI, lldb is unable to set breakpoints on specific C++ exceptions or it does not resolve the name correctly.

I set a breakpoint for std::underflow_error and then using the lldb breakpoint list command, determined it only places a symbolic breakpoint on std::underflow_error:

9: name = 'std::underflow_error', locations = 0 (pending)

I suspect that lldb never resolves std::underflow_error to the constructor. C++ name mangling might have something to do with it too.

If you create a breakpoint for all C++ exception, you will see it creates a symbolic breakpoint on __cxa_throw:

10: name = '__cxa_throw', locations = 1, resolved = 1

  10.1: where = libc++abi.dylib`__cxa_throw, address = 0x01cefa44, resolved, hit count = 0

You might be able to put a breakpoint in the constructor of the exception you are interested in, assuming it is instantiated and thrown at the same point.