# adapted some code from https://github.com/python/cpython/blob/2.7/Tools/gdb/libpython.py

class PyBtLinked(gdb.Command):
    def __init__(self):
        gdb.Command.__init__ (self,
                              "py-bt-linked",
                              gdb.COMMAND_STACK,
                              gdb.COMPLETE_NONE)


    def invoke(self, args, from_tty):
        try:
            print('Traceback (most recent call first):')

            def p_stack(filename, lineno, funcname):
                print('  File "{}", line {}, in {}'.format(
                    filename if filename is not None else '<possibly built-in>',
                    lineno, funcname))

                if filename is not None:
                    import os
                    try:
                        cwd = os.readlink('/proc/{}/cwd'.format(gdb.selected_inferior().pid))
                    except IOError:
                        pass
                    else:
                        filename = os.path.join(cwd, filename)
                    
                    try:
                        file = open(filename, 'rb')
                    except IOError:
                        print('    <can\'t open "{}">'.format(filename))
                    else:
                        with file:
                            print('    ' +
                                  file.read().split(b'\n')[int(lineno)-1]
                                  .decode('utf-8').strip())

            def pystr(pystrptr):
                assert pystrptr['ob_type']['tp_name'].string() == 'str'
                pystrptr = pystrptr.cast(gdb.lookup_type('PyStringObject').pointer())
                field_ob_size = int(pystrptr['ob_size'])
                field_ob_sval = pystrptr['ob_sval']
                return ''.join(chr(field_ob_sval[i]) for i in range(field_ob_size))

            def addr2line(code, addrq):
                co_lnotab = pystr(code['co_lnotab'])
                lineno = int(code['co_firstlineno'])

                addr = 0
                for addr_incr, line_incr in zip(co_lnotab[::2], co_lnotab[1::2]):
                    addr += ord(addr_incr)
                    if addr > addrq:
                        return lineno
                    lineno += ord(line_incr)
                return lineno

            filename, lineno = None, '?'

            frame = None

            gdbframe = gdb.newest_frame()
            while not frame:
                gdbframe = gdbframe.older()

                regs = ['rax', 'rbx', 'rcx', 'rdx', 'rsi', 'rdi', 'rbp', 'r8', 'r9', 'r10', 'r11', 'r12', 'r13', 'r14', 'r15']
                for reg in regs:
                    r = gdbframe.read_register(reg)
                    try:
                        r = r.cast(gdb.lookup_type('PyFrameObject').pointer())
                        if r['ob_type']['tp_name'].string() == 'frame':
                            frame = r
                    except Exception:
                        continue

            while frame:
                code = frame['f_code']
                filename = pystr(code['co_filename'])
                lineno = addr2line(code, int(frame['f_lasti']))
                funcname = pystr(code['co_name'])

                p_stack(filename, lineno, funcname)

                frame = frame['f_back']
        except Exception:
            import traceback
            traceback.print_exc()

PyBtLinked()