#
# gdb helper commands and functions for Linux kernel debugging
#
#  common utilities
#
# Copyright (c) Siemens AG, 2011-2013
#
# Authors:
#  Jan Kiszka <jan.kiszka@siemens.com>
#
# This work is licensed under the terms of the GNU GPL version 2.
#

import gdb


class CachedType:
    def __init__(self, name):
        self._type = None
        self._name = name

    def _new_objfile_handler(self, event):
        self._type = None
        gdb.events.new_objfile.disconnect(self._new_objfile_handler)

    def get_type(self):
        if self._type is None:
            self._type = gdb.lookup_type(self._name)
            if self._type is None:
                raise gdb.GdbError(
                    "cannot resolve type '{0}'".format(self._name))
            if hasattr(gdb, 'events') and hasattr(gdb.events, 'new_objfile'):
                gdb.events.new_objfile.connect(self._new_objfile_handler)
        return self._type


long_type = CachedType("long")


def get_long_type():
    global long_type
    return long_type.get_type()


def offset_of(typeobj, field):
    element = gdb.Value(0).cast(typeobj)
    return int(str(element[field].address).split()[0], 16)


def container_of(ptr, typeobj, member):
    return (ptr.cast(get_long_type()) -
            offset_of(typeobj, member)).cast(typeobj)


class ContainerOf(gdb.Function):
    """Return pointer to containing data structure.

$container_of(PTR, "TYPE", "ELEMENT"): Given PTR, return a pointer to the
data structure of the type TYPE in which PTR is the address of ELEMENT.
Note that TYPE and ELEMENT have to be quoted as strings."""

    def __init__(self):
        super(ContainerOf, self).__init__("container_of")

    def invoke(self, ptr, typename, elementname):
        return container_of(ptr, gdb.lookup_type(typename.string()).pointer(),
                            elementname.string())

ContainerOf()