diagnose_unwind.py   [plain text]

# This implements the "diagnose-unwind" command, usually installed
# in the debug session like
#   command script import lldb.diagnose
# it is used when lldb's backtrace fails -- it collects and prints
# information about the stack frames, and tries an alternate unwind
# algorithm, that will help to understand why lldb's unwind algorithm
# did not succeed.

import optparse
import lldb
import re
import shlex

# Print the frame number, pc, frame pointer, module UUID and function name
# Returns the SBModule that contains the PC, if it could be found
def backtrace_print_frame (target, frame_num, addr, fp):
  process = target.GetProcess()
  addr_for_printing = addr
  addr_width = process.GetAddressByteSize() * 2
  if frame_num > 0:
    addr = addr - 1

  sbaddr = lldb.SBAddress()
  try:
    sbaddr.SetLoadAddress(addr, target)
    module_description = ""
    if sbaddr.GetModule():
      module_filename = ""
      module_uuid_str = sbaddr.GetModule().GetUUIDString()
      if module_uuid_str == None:
        module_uuid_str = ""
      if sbaddr.GetModule().GetFileSpec():
        module_filename = sbaddr.GetModule().GetFileSpec().GetFilename()
        if module_filename == None:
          module_filename = ""
      if module_uuid_str != "" or module_filename != "":
        module_description = '%s %s' % (module_filename, module_uuid_str)
  except Exception:
    print '%2d: pc==0x%-*x fp==0x%-*x' % (frame_num, addr_width, addr_for_printing, addr_width, fp)
    return

  sym_ctx = target.ResolveSymbolContextForAddress(sbaddr, lldb.eSymbolContextEverything)
  if sym_ctx.IsValid() and sym_ctx.GetSymbol().IsValid():
    function_start = sym_ctx.GetSymbol().GetStartAddress().GetLoadAddress(target)
    offset = addr - function_start
    print '%2d: pc==0x%-*x fp==0x%-*x %s %s + %d' % (frame_num, addr_width, addr_for_printing, addr_width, fp, module_description, sym_ctx.GetSymbol().GetName(), offset)
  else:
    print '%2d: pc==0x%-*x fp==0x%-*x %s' % (frame_num, addr_width, addr_for_printing, addr_width, fp, module_description)
  return sbaddr.GetModule()

# A simple stack walk algorithm that follows the frame chain.
# Returns a two-element list; the first element is a list of modules
# seen and the second element is a list of addresses seen during the backtrace.
def simple_backtrace(debugger):
  target = debugger.GetSelectedTarget()
  process = target.GetProcess()
  cur_thread = process.GetSelectedThread()

  initial_fp = cur_thread.GetFrameAtIndex(0).GetFP()

  # If the pseudoreg "fp" isn't recognized, on arm hardcode to r7 which is correct for Darwin programs.
  if initial_fp == lldb.LLDB_INVALID_ADDRESS and target.triple[0:3] == "arm":
    for reggroup in cur_thread.GetFrameAtIndex(1).registers:
      if reggroup.GetName() == "General Purpose Registers":
        for reg in reggroup:
          if reg.GetName() == "r7":
            initial_fp = int (reg.GetValue(), 16)

  module_list = []
  address_list = [cur_thread.GetFrameAtIndex(0).GetPC()]
  this_module = backtrace_print_frame (target, 0, cur_thread.GetFrameAtIndex(0).GetPC(), initial_fp)
  print_stack_frame (process, initial_fp)
  print ""
  if this_module != None:
    module_list.append (this_module)
  if cur_thread.GetNumFrames() < 2:
    return [module_list, address_list]

  cur_fp = process.ReadPointerFromMemory (initial_fp, lldb.SBError())
  cur_pc = process.ReadPointerFromMemory (initial_fp + process.GetAddressByteSize(), lldb.SBError())

  frame_num = 1

  while cur_pc != 0 and cur_fp != 0 and cur_pc != lldb.LLDB_INVALID_ADDRESS and cur_fp != lldb.LLDB_INVALID_ADDRESS:
    address_list.append (cur_pc)
    this_module = backtrace_print_frame (target, frame_num, cur_pc, cur_fp)
    print_stack_frame (process, cur_fp)
    print ""
    if this_module != None:
      module_list.append (this_module)
    frame_num = frame_num + 1
    next_pc = 0
    next_fp = 0
    if target.triple[0:6] == "x86_64" or target.triple[0:4] == "i386" or target.triple[0:3] == "arm":
      error = lldb.SBError()
      next_pc = process.ReadPointerFromMemory(cur_fp + process.GetAddressByteSize(), error)
      if not error.Success():
        next_pc = 0
      next_fp = process.ReadPointerFromMemory(cur_fp, error)
      if not error.Success():
        next_fp = 0
    # Clear the 0th bit for arm frames - this indicates it is a thumb frame
    if target.triple[0:3] == "arm" and (next_pc & 1) == 1:
      next_pc = next_pc & ~1
    cur_pc = next_pc
    cur_fp = next_fp
  this_module = backtrace_print_frame (target, frame_num, cur_pc, cur_fp)
  print_stack_frame (process, cur_fp)
  print ""
  if this_module != None:
    module_list.append (this_module)
  return [module_list, address_list]

def print_stack_frame(process, fp):
  if fp == 0 or fp == lldb.LLDB_INVALID_ADDRESS or fp == 1:
    return
  addr_size = process.GetAddressByteSize()
  addr = fp - (2 * addr_size)
  i = 0
  outline = "Stack frame from $fp-%d: " % (2 * addr_size)
  error = lldb.SBError()
  try:
    while i < 5 and error.Success():
      address = process.ReadPointerFromMemory(addr + (i * addr_size), error)
      outline += " 0x%x" % address
      i += 1
    print outline
  except Exception:
    return

def diagnose_unwind(debugger, command, result, dict):
  """
Gather diagnostic information to help debug incorrect unwind (backtrace) 
behavior in lldb.  When there is a backtrace that doesn't look
correct, run this command with the correct thread selected and a
large amount of diagnostic information will be printed, it is likely
to be helpful when reporting the problem.
  """

  command_args = shlex.split(command)
  parser = create_diagnose_unwind_options()
  try:
    (options, args) = parser.parse_args(command_args)
  except:
   return
  target = debugger.GetSelectedTarget()
  if target:
    process = target.GetProcess()
    if process:
      thread = process.GetSelectedThread()
      if thread:
        lldb_versions_match = re.search(r'[lL][lL][dD][bB]-(\d+)([.](\d+))?([.](\d+))?', debugger.GetVersionString())
        lldb_version = 0
        lldb_minor = 0
        if len(lldb_versions_match.groups()) >= 1 and lldb_versions_match.groups()[0]:
          lldb_major = int(lldb_versions_match.groups()[0])
        if len(lldb_versions_match.groups()) >= 5 and lldb_versions_match.groups()[4]:
          lldb_minor = int(lldb_versions_match.groups()[4])

        modules_seen = []
        addresses_seen = []

        print 'LLDB version %s' % debugger.GetVersionString()
        print 'Unwind diagnostics for thread %d' % thread.GetIndexID()
        print ""
        print "============================================================================================="
        print ""
        print "OS plugin setting:"
        debugger.HandleCommand("settings show target.process.python-os-plugin-path")
        print ""
        print "Live register context:"
        thread.SetSelectedFrame(0)
        debugger.HandleCommand("register read")
        print ""
        print "============================================================================================="
        print ""
        print "lldb's unwind algorithm:"
        print ""
        frame_num = 0
        for frame in thread.frames:
          if not frame.IsInlined():
            this_module = backtrace_print_frame (target, frame_num, frame.GetPC(), frame.GetFP())
            print_stack_frame (process, frame.GetFP())
            print ""
            if this_module != None:
              modules_seen.append (this_module)
            addresses_seen.append (frame.GetPC())
            frame_num = frame_num + 1
        print ""
        print "============================================================================================="
        print ""
        print "Simple stack walk algorithm:"
        print ""
        (module_list, address_list) = simple_backtrace(debugger)
        if module_list and module_list != None:
          modules_seen += module_list
        if address_list and address_list != None:
          addresses_seen = set(addresses_seen)
          addresses_seen.update(set(address_list))

        print ""
        print "============================================================================================="
        print ""
        print "Modules seen in stack walks:"
        print ""
        modules_already_seen = set()
        for module in modules_seen:
          if module != None and module.GetFileSpec().GetFilename() != None:
            if not module.GetFileSpec().GetFilename() in modules_already_seen:
              debugger.HandleCommand('image list %s' % module.GetFileSpec().GetFilename())
              modules_already_seen.add(module.GetFileSpec().GetFilename())

        print ""
        print "============================================================================================="
        print ""
        print "Disassembly ofaddresses seen in stack walks:"
        print ""
        additional_addresses_to_disassemble = addresses_seen
        for frame in thread.frames:
          if not frame.IsInlined():
            print "--------------------------------------------------------------------------------------"
            print ""
            print "Disassembly of %s, frame %d, address 0x%x" % (frame.GetFunctionName(), frame.GetFrameID(), frame.GetPC())
            print ""
            if target.triple[0:6] == "x86_64" or target.triple[0:4] == "i386":
              debugger.HandleCommand('disassemble -F att -a 0x%x' % frame.GetPC())
            else:
              debugger.HandleCommand('disassemble -a 0x%x' % frame.GetPC())
            if frame.GetPC() in additional_addresses_to_disassemble:
              additional_addresses_to_disassemble.remove (frame.GetPC())

        for address in list(additional_addresses_to_disassemble):
          print "--------------------------------------------------------------------------------------"
          print ""
          print "Disassembly of 0x%x" % address
          print ""
          if target.triple[0:6] == "x86_64" or target.triple[0:4] == "i386":
            debugger.HandleCommand('disassemble -F att -a 0x%x' % address)
          else:
            debugger.HandleCommand('disassemble -a 0x%x' % address)

        print ""
        print "============================================================================================="
        print ""
        additional_addresses_to_show_unwind = addresses_seen
        for frame in thread.frames:
          if not frame.IsInlined():
            print "--------------------------------------------------------------------------------------"
            print ""
            print "Unwind instructions for %s, frame %d" % (frame.GetFunctionName(), frame.GetFrameID())
            print ""
            debugger.HandleCommand('image show-unwind -a "0x%x"' % frame.GetPC())
            if frame.GetPC() in additional_addresses_to_show_unwind:
              additional_addresses_to_show_unwind.remove (frame.GetPC())

        for address in list(additional_addresses_to_show_unwind):
          print "--------------------------------------------------------------------------------------"
          print ""
          print "Unwind instructions for 0x%x" % address
          print ""
          debugger.HandleCommand('image show-unwind -a "0x%x"' % address)

def create_diagnose_unwind_options():
  usage = "usage: %prog"
  description='''Print diagnostic information about a thread backtrace which will help to debug unwind problems'''
  parser = optparse.OptionParser(description=description, prog='diagnose_unwind',usage=usage)
  return parser

lldb.debugger.HandleCommand('command script add -f %s.diagnose_unwind diagnose-unwind' % __name__)
print 'The "diagnose-unwind" command has been installed, type "help diagnose-unwind" for detailed help.'