Failed attempt at using GDB unwinders for Go core files

btg.py

try:
    from gdb.unwinder import Unwinder, register_unwinder
except ImportError:
    Unwinder = None

if Unwinder is not None:
    class FrameID(object):
        def __init__(self, sp, pc):
            self.sp = sp
            self.pc = pc

    class GoUnwinder(Unwinder):
        def __init__(self):
            super(GoUnwinder, self).__init__("go-unwinder")
            self.enabled = False

        def __call__(self, pending_frame):
            # print("GoUnwinder.__call__", pending_frame, self.frame_id)
            # This only applies to the first frame.
            self.enabled = False

            # Maybe they need to be the exact right types?
            # Doesn't seem to help.
            # pc = pending_frame.read_register('rip')
            # sp = pending_frame.read_register('rsp')
            # self.frame_id.pc = self.frame_id.pc.cast(pc.type)
            # self.frame_id.sp = self.frame_id.sp.cast(sp.type)
            # print(self.frame_id.pc, self.frame_id.sp)

            # Ignore registers in pending_frame. Use stashed PC/SP.
            unwind_info = pending_frame.create_unwind_info(self.frame_id)

            # Maybe they need to also be saved registers?
            # Doesn't seem to help.
            # unwind_info.add_saved_register('rip', self.frame_id.pc)
            # unwind_info.add_saved_register('rsp', self.frame_id.sp)

            return unwind_info
    goUnwinder = GoUnwinder()
    register_unwinder(None, goUnwinder, replace=True)

    def ngoroutine(self, arg, _from_tty):
        goid, cmd = arg.split(None, 1)
        goid = gdb.parse_and_eval(goid)
        pc, sp = find_goroutine(int(goid))
        if not pc:
            print("No such goroutine: ", goid)
            return
        try:
            #python3 / newer versions of gdb
            pc = int(pc)
        except gdb.error:
            pc = int(str(pc).split(None, 1)[0], 16)
        goUnwinder.frame_id = FrameID(gdb.Value(sp), gdb.Value(pc))
        goUnwinder.enabled = True
        try:
            gdb.execute(cmd)
        finally:
            goUnwinder.enabled = False

    GoroutineCmd.invoke = ngoroutine                                 

I have no special insight as to licensing w.r.t. to this code, but I would have assumed that gdb is licensed under the standard GNU licensing terms. Under binutils-gdb there are files calling COPYING and COPYING3 (and others as well) that state that all of the code is free to copy,
modify and utilize.

@BDHorn Have a look at this. golang/go#17575 (comment) This is not my final version but as i do not have authorization this is the extent of what i can contribute