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dps_like_for_gdb.py
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dps_like_for_gdb.py
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#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# dps_like.py - A dps like function for your GDB
# Copyright (C) 2012 Axel "0vercl0k" Souchet - http://www.twitter.com/0vercl0k
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
import gdb
import re
class CommandDumpPointersWithSymbol(gdb.Command):
"""
This class aims to do the same thing (approx yeah) as the dps' windbg command does:
it displays one pointer per line with its symbol (if there is one)
Usage:
dps <register or address> <positive int>
It will display n [D/Q]WORDs pointed by the register/address
"""
def __init__(self):
gdb.Command.__init__(self, 'dps', gdb.COMMAND_STACK)
self.p_char = gdb.lookup_type('char').pointer()
self.p_long = gdb.lookup_type('long').pointer()
self.is_x86 = self.p_long.sizeof == 4
# retrieve the memory mapping
self.zones = self._parse_info_files()
def _get_cpu_register(self, reg):
"""
Get the value holded by a CPU register
"""
expr = ''
if reg[0] == '$':
expr = reg
else:
expr = '$' + reg
try:
val = self._normalize_long(long(gdb.parse_and_eval(expr)))
except:
print "Hum, have you ran the process ? I can't retrieve any register."
return None
return val
def _normalize_long(self, l):
return (0xffffffff if self.is_x86 else 0xffffffffffffffff) & l
def _long_to_str(self, l):
return ('%#.8x' if self.is_x86 else '%#.16x') % l
def _deref_long_from_addr(self, addr):
"""
Get the value pointed by addr
"""
# now cast + deref
val = gdb.Value(addr).cast(self.p_long).dereference()
return self._normalize_long(long(val))
def _where_it_points(self, address):
"""
Walk out the memory mapping and try to find where the address is pointing
"""
info = []
for zone in self.zones:
if zone['start'] <= address < zone['end']:
temp = zone['section_name']
# NB: it exists gdb.solid_name(addr) to retrieve the sharedlibrary name if the address points in its range
if zone['module']:
temp += '!%s' % zone['module']
# we know where the address points
info.append(temp)
break
# but let's try to have other/additional info
r = self._get_additionnal_info(address, zone['section_name'])
if r:
info.append(r)
return info
def _is_register(self, s):
"""
Is it a valid register ?
"""
x86_reg = ['eax', 'ebx', 'ecx', 'edx', 'esi', 'edi', 'esp', 'ebp', 'eip']
x64_reg = ['rax', 'rbx', 'rcx', 'rdx', 'rsi', 'rdi', 'rsp', 'rbp', 'rip'] + ['r%d' % i for i in range(8, 16)]
if s[0] == '$':
s = s[1:]
if s in (x86_reg if self.is_x86 else x64_reg):
return True
return False
def _is_pointing_on_string(self, addr):
"""
Is address is a pointer on a string ?
Only strings with >= 3 characters are allowed
"""
# we try to see if addr is a pointer on an ASCII string
s = gdb.Value(addr).cast(self.p_char)
try:
s = s.string()
except:
return None
if len(s) > 3:
# we consider it as a true string if it has at last 3 characters
# but we will display only the first 50 chars
return (s[:50] + '[...]' if len(s) > 50 else s)
return None
def _parse_info_files(self):
"""
Creates a list of dictionnaries where you can find the start/end of all sharelibrary sections
"""
r = gdb.execute('info files', to_string = True)
zones = []
for line in r.splitlines():
if line.find(' is ') == -1:
continue
memrange, where = line.split(' is ', 1)
start, end = memrange.split(' - ', 1)
section, module = where, ''
# it's a section in a sharedlibrary
if where.find(' in ') != -1:
section, module = where.split(' in ')
zones.append({
'start' : int(start.lstrip(), 16),
'end' : int(end, 16),
'section_name' : section,
'module' : module
})
return zones
def _clean_disass(self, disass):
"""
Clean the disassembly
When you have 'mov eax, [ebx]', it returns 'mov eax, [ebx]'
"""
return re.sub(r'\s+', ' ', disass)
def _get_additionnal_info(self, addr, section):
"""
Try to know if the address is a string pointer, if not it try to disassemble the first instruction
"""
# before any test, we want to know if the memory is accessible
try:
self._deref_long_from_addr(addr)
except:
# memory isn't accessible
return None
# we try to see if addr is a pointer on an ASCII string
r = self._is_pointing_on_string(addr)
if r != None and len(r) > 1:
# we consider it as a true string
return 'String(%s)' % repr(r)
# try to disassembly it
r = gdb.execute('x/i %#x' % addr, to_string = True)
function, instr = r.split(':', 1)
# clean the instruction part
clean_disass = self._clean_disass(instr)
# try to obtain the function name
function_names = re.findall('<(.+)>', function)
# we prepare the signature
signature = clean_disass
if len(function_names) > 0:
signature += 'found in "%s"' % function_names[0]
return signature
def invoke(self, arg, from_tty):
"""
The core of the command
"""
arguments = arg.split(' ')
assert(len(arguments) == 2)
r, npointers = arguments
pointer_address = 0
if self._is_register(r):
pointer_address = self._get_cpu_register(r)
if not pointer_address:
return
else:
try:
# we assume it's an address
pointer_address = int(r, 16)
except:
print 'The first argument should be wether an address or a register, please read the "help dps"'
return
for n in range(int(npointers)):
try:
value = self._deref_long_from_addr(pointer_address)
except:
print 'There is not allocated memory at %s' % self._long_to_str(pointer_address)
return
print '%.4d - [%s] = %s - %s' % (n, self._long_to_str(pointer_address), self._long_to_str(value), ' - '.join(self._where_it_points(value)))
pointer_address += self.p_long.sizeof
CommandDumpPointersWithSymbol()