This script finds the registers saved on the stack in each frame.As ESI, EDI usually serves as the 'this' ptr to an object, that's why it's named findthis. It is written in python. An extension pykd(http://pykd.codeplex.com/) needs to be installed and loaded before running the script in Windbg.Check http://nicoster.github.io/find-this-ptr-within…

findthis.py

desc = '''
Author: Nick X(nicoster@gmail)   

This scripts finds the registers saved on the stack in each frame.
As ESI, EDI usually serves as the 'this' ptr to an object, that's why it's named findthis

Usage:
!py findthis [debug|desc]

Due to a bug in pykd that it won't allow modifying a file once it's loaded by '!py' cmd. 
when you're debugging a script, we suggest you run the script this way, always do a load/unload of the pykd extension.

.load pykd.pyd;!py findthis\findthis;.unload pykd.pyd

Currently support x86 only.

Oct 2013: Created.
Nov 2013: Refactor the output to align with that of 'kL' command
Mar 2015: 
	. handle 'and esp, 0xfffffff8' in parsing assembly code
	. remove the duplication of registers
	. attempt to take advantage of 'dv /v /t this' command but in vain
	. better debug logging
'''
 
 
import sys
import re
import tempfile
from pykd import *
 
pid = None
try:
	pid = dbgCommand('|').split()[3]
except:
	pass
 
cache = tempfile.gettempdir() + '\\findthis.' + pid
debug = False
system_modules = ['ntdll', 'kernel32', 'user32', 'kernelbase']
registers = ['ebx', 'ecx', 'edx', 'esi', 'edi', 'eax']
this_registers = ['esi', 'edi', 'ebx', 'edx', 'ecx']
prologs = {
	'_EH_prolog3': {16:'ebx', 20: 'esi', 24: 'edi'},
	'_EH_prolog3_GS': {16: 'ebx', 20: 'esi', 24: 'edi'},
	'_SEH_prolog4': {16: 'ebx', 20: 'esi', 24: 'edi'}	
	}

def dbg(*args):
	if debug:
		for arg in args:
			print arg,
		print ''

def handle_prolog(prolog, offset, results):
	if prolog not in prologs: return False
	for k,v in prologs[prolog].iteritems():
		results[k + offset] = v
	return True

def IsAmbiguousSymbol(func):
	funcs = dbgCommand('x ' + func.strip()).splitlines()
	return len(funcs)

def parseFrameSymbol(frames, i, func_offset):
	try:
		ip = None
		if i == len(frames) - 1:	# last frame
			ip = hex(reg('eip'))
		else:
			ip = frames[i + 1].split()[2]
		int(ip, 16)		# make sure it's a number

		cmd = 'u ' + ip + '-' + func_offset + ' L10'
		dbg(cmd)

		return dbgCommand(cmd)
	except BaseException, e:
		dbg(dbgCommand('ln ' + ip + '-' + func_offset), e)

	return None

def formatRegister(this, val, register):
	dummy, class_name = this if this else (None, None)

	if class_name and val and register in this_registers:
		return register + ':<link cmd="dt ' + class_name + ' %08x' % val + '; .echo;.echo View this in Watch: (' \
			+ class_name + '*)%#x' % val  + '; !py ' + sys.argv[0] + ' showcachelink">%08x' % val + '</link> '
	else:
		return register + ':%08x' % val + ' '

# find this register from PDB. but this doesn't really help enough. 
# from example, ecx is marked as the this ptr. but in the function prologue ecx is stored in esi immediately and has never been stored in the stack
def getPrevClass(frame_index, func):
	dbgCommand('.frame ' + frame_index)
	this = dbgCommand('dv /v /t this').split()
	# it's something like: [u'@esi', u'class', u'Foo', u'*', u'this', u'=', u'0x00c58cf8']
	if this and this[0] and this[0].startswith('@') and len(this) >= 7:
		return (this[0][1:], ' '.join(this[2:-4]))

	return (None, func.rsplit('::', 1)[0] if '::' in func else None)


def find_this():
	dprintln('findthis v1.0. nicoster@gmail. 2013. All Rights Reserved.')
	dprintln('<link cmd="!py findthis desc">Details</link>\n', True)
 
	output = []
	prev_class = None
	stack = dbgCommand('knL100')
	frames = stack.splitlines()[:0:-1]
	for i in range(len(frames)):
		dbg('\n\n-------\nprev-class:', prev_class)
		frame = frames[i]
		output.append(frame)
		frame_index = None
		try:
			frame_index, ebp, ret_addr, symbol = frame.split(None, 3)
			dbg('symbol: ' + symbol)
			ebp = int(ebp, 16)
		except:
			prev_class = None
			continue
 
		module = symbol.split('!')[0]
		if module.lower() in system_modules and not prev_class:
			prev_class = None
			continue
 
 		func_offset = None
 		func = None
 		if '+' in symbol:
			func, func_offset = symbol.split('+')
		else:
			func = symbol
 
		escaped_func = '@@(' + func + ')' if ' ' in func else func
		try: code = dbgCommand('u ' + escaped_func + ' L10')
		except BaseException, e:
			if IsAmbiguousSymbol(func):
			  	code = parseFrameSymbol(frames, i, func_offset)
			  	if not code:
					# prev_class should be obtained, as the registers might be availabe in next frame, thus we allow users to decode register via DML
					prev_class = getPrevClass(frame_index, func)
					continue
			else:
				dbg(e)
				# prev_class should be obtained, as the registers might be availabe in next frame, thus we allow users to decode register via DML
				prev_class = getPrevClass(frame_index, func)
				continue
 
		offset = 0
		results = {}
		for line in code.split('\n'):
			dbg(line)

			# if not address, this line is not code
			try:
				addr, bytes, opcode, operands  = line.split(None, 3)
				int(addr, 16)
			except:
				continue
 
			if opcode == 'push':
				offset += 4
				if operands not in results.values():
					results[offset] = operands
				continue

			if opcode == 'pop':
				offset -= 4
				results = dict([(k, v) for k, v in results.items() if v != operands])	# remove a reg (operands) from results
				continue

			# to deal with instructions like 'and esp,0FFFFFFF8h'
			if opcode == 'and' and operands.startswith('esp'):
				instant_value = operands.split(',')[1]
				if instant_value.endswith('h'):
					instant_value = instant_value[:-1]

				esp = (ebp - offset + 4) & int(instant_value, 16)
				offset = ebp - esp + 4
				dbg('%08x' % ebp, '%08x' % esp, offset)
 
			if opcode == 'sub' and operands.startswith('esp'):
				size = operands.split(',')[1]
				if size.endswith('h'):
					size = size[:-1]
				offset += int(size, 16)
				continue
 
			if opcode == 'call':
				if 'EH_prolog' in operands:
					prolog = operands.split()[0].split('!')[1]
					# it should have something like 'push 8'
					assert(len(results) < 3 and results[4])
					size = results[4]
					if size.endswith('h'):
						size = size[:-1]
					ret = handle_prolog(prolog, int(size, 16) + offset, results)
					if not ret:
						dbg('unhandled prolog:', operands)
 
				break

			if opcode.startswith('j'):
				break
 
		output_regs = ''
		sorted_results = sorted(results.iteritems(), key=lambda d:d[0])
		for offset, register in sorted_results:
			dbg(offset, register)
			if register in registers:
				output_regs += formatRegister(prev_class, ptrDWord(ebp - offset + 4), register)
		if output_regs and len(output) > 1: output[-2] += ' [' + output_regs + ']'
 
		prev_class = getPrevClass(frame_index, func)

	# associate the first frame with the registers
	output_regs = ''
	for register in this_registers:
		output_regs += formatRegister(prev_class, reg(register), register)
	output[-1] += ' [' + output_regs + ']'


	print 'Possible this ptrs have been highlighted. Click to decode them respectively.\n'
	output = '\n'.join(output[::-1])
	dprintln(output, True)
	try:
		fp = open(cache, 'w')
		fp.write(output)
		fp.close()
	except:
		pass

def main(argv):
	if len(argv) == 2:
		if argv[1] == "desc":
			print desc
		elif argv[1] == 'cache':
			try:
				fp = open(cache, 'r')
				dprintln(fp.read(), True)
				fp.close()
			except:
				pass
		elif argv[1] == 'showcachelink':
			dprintln('\n<link cmd="!py ' + sys.argv[0] + ' cache">Show this ptrs</link>', True)
		elif argv[1] == 'debug':
			global debug
			debug = True
			main([])
	else:
		find_this()
 
if __name__ == "__main__":
	main(sys.argv)