# pahole command for gdb

import gdb

class Pahole (gdb.Command):
    """Show the holes in a structure.
This command takes a single argument, a type name.
It prints the type and displays comments showing where holes are."""

    def __init__ (self):
        super (Pahole, self).__init__ ("pahole", gdb.COMMAND_NONE,
                                       gdb.COMPLETE_SYMBOL)

    @staticmethod
    def strip (type):
        while type.code () == gdb.TYPE_CODE_TYPEDEF:
            type = type.target ()
        return type

    def pahole (self, type, level, name):
        if name is None:
            name = ''
        tag = type.tag ()
        if tag is None:
            tag = ''
        print '%sstruct %s {' % (' ' * (2 * level), tag)
        bitpos = 0
        for field in type.fields ():
            # Skip static fields.
            if not hasattr (field, ('bitpos')):
                continue

            ftype = self.strip (field.type)

            if bitpos != field.bitpos:
                hole = field.bitpos - bitpos
                print '  /* XXX %d bit hole, try to pack */' % hole
                bitpos = field.bitpos
            if field.bitsize > 0:
                fieldsize = field.bitsize
            else:
                # TARGET_CHAR_BIT here...
                fieldsize = 8 * ftype.sizeof ()

            # TARGET_CHAR_BIT
            print ' /* %3d %3d */' % (int (bitpos / 8), int (fieldsize / 8)),
            bitpos = bitpos + fieldsize

            if ftype.code () == gdb.TYPE_CODE_STRUCT:
                self.pahole (ftype, level + 1, field.name)
            else:
                print ' ' * (2 + 2 * level),
                print '%s %s' % (str (ftype), field.name)

        print ' ' * (14 + 2 * level),
        print '} %s' % name

    def invoke (self, arg, from_tty):
        type = gdb.Type (arg)
        type = self.strip (type)
        if type.code () != gdb.TYPE_CODE_STRUCT:
            raise '%s is not a struct type' % arg
        print ' ' * 14,
        self.pahole (type, 0, '')

Pahole()