.lldbinit

command script import ~/Library/lldb/sniff_objc_exception_throw.py

sniff_objc_exception_throw.py

import lldb
 
def GetFirstArgumentAsValue(target, frame):
    platform = target.triple
    registers = frame.regs[0]
    # Note: I assume the PC is at the first instruction of the function, before the stack and registers have been modified.
    if platform.startswith('x86_64'):
        return registers.GetChildMemberWithName("rdi")
    elif platform.startswith('i386'):
        espValue = registers.GetChildMemberWithName("esp")
        address = espValue.GetValueAsUnsigned() + target.addr_size
        return espValue.CreateValueFromAddress('arg0', address, target.FindFirstType('id'))
    elif platform.startswith('arm64'):
        return registers.GetChildMemberWithName("x0")
    else:
        return registers.GetChildMemberWithName("r0")
 
def command(debugger, user_input, result, unused):
    target = debugger.GetSelectedTarget()
    frame = target.GetProcess().GetSelectedThread().GetFrameAtIndex(0)
    description = GetFirstArgumentAsValue(target, frame).GetObjectDescription()
    if description is None:
        output = "I couldn't get the description of the exception being thrown."
    else:
        output = "Description of exception being thrown: " + repr(description)
    result.PutCString(output)
    return None
 
def __lldb_init_module(debugger, unused):
    debugger.HandleCommand('command script add --function sniff_objc_exception_throw.command sniff_objc_exception_throw')

arm64 has renamed the registers from r$ to x$.
Because this adds yet another branch, obtaining the platform, and register–tuple has been extracted to local variables.