1# This implements the "diagnose-unwind" command, usually installed
2# in the debug session like
3#   command script import lldb.diagnose
4# it is used when lldb's backtrace fails -- it collects and prints
5# information about the stack frames, and tries an alternate unwind
6# algorithm, that will help to understand why lldb's unwind algorithm
7# did not succeed.
8
9import optparse
10import lldb
11import re
12import shlex
13
14# Print the frame number, pc, frame pointer, module UUID and function name
15def backtrace_print_frame (target, frame_num, addr, fp):
16  process = target.GetProcess()
17  addr_for_printing = addr
18  addr_width = process.GetAddressByteSize() * 2
19  if frame_num > 0:
20    addr = addr - 1
21
22  sbaddr = lldb.SBAddress()
23  try:
24    sbaddr.SetLoadAddress(addr, target)
25    module_description = ""
26    if sbaddr.GetModule():
27      module_filename = ""
28      module_uuid_str = sbaddr.GetModule().GetUUIDString()
29      if module_uuid_str == None:
30        module_uuid_str = ""
31      if sbaddr.GetModule().GetFileSpec():
32        module_filename = sbaddr.GetModule().GetFileSpec().GetFilename()
33        if module_filename == None:
34          module_filename = ""
35      if module_uuid_str != "" or module_filename != "":
36        module_description = '%s %s' % (module_filename, module_uuid_str)
37  except Exception:
38    print '%2d: pc==0x%-*x fp==0x%-*x' % (frame_num, addr_width, addr_for_printing, addr_width, fp)
39    return
40
41  sym_ctx = target.ResolveSymbolContextForAddress(sbaddr, lldb.eSymbolContextEverything)
42  if sym_ctx.IsValid() and sym_ctx.GetSymbol().IsValid():
43    function_start = sym_ctx.GetSymbol().GetStartAddress().GetLoadAddress(target)
44    offset = addr - function_start
45    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)
46  else:
47    print '%2d: pc==0x%-*x fp==0x%-*x %s' % (frame_num, addr_width, addr_for_printing, addr_width, fp, module_description)
48
49# A simple stack walk algorithm that follows the frame chain after the first two frames.
50def simple_backtrace(debugger):
51  target = debugger.GetSelectedTarget()
52  process = target.GetProcess()
53  cur_thread = process.GetSelectedThread()
54
55  backtrace_print_frame (target, 0, cur_thread.GetFrameAtIndex(0).GetPC(), cur_thread.GetFrameAtIndex(0).GetFP())
56  if cur_thread.GetNumFrames() < 2:
57    return
58
59  cur_fp = cur_thread.GetFrameAtIndex(1).GetFP()
60  cur_pc = cur_thread.GetFrameAtIndex(1).GetPC()
61
62  # If the pseudoreg "fp" isn't recognized, on arm hardcode to r7 which is correct for Darwin programs.
63  if cur_fp == lldb.LLDB_INVALID_ADDRESS and target.triple[0:3] == "arm":
64    for reggroup in cur_thread.GetFrameAtIndex(1).registers:
65      if reggroup.GetName() == "General Purpose Registers":
66        for reg in reggroup:
67          if reg.GetName() == "r7":
68            cur_fp = int (reg.GetValue(), 16)
69
70  frame_num = 1
71
72  while cur_pc != 0 and cur_fp != 0 and cur_pc != lldb.LLDB_INVALID_ADDRESS and cur_fp != lldb.LLDB_INVALID_ADDRESS:
73    backtrace_print_frame (target, frame_num, cur_pc, cur_fp)
74    frame_num = frame_num + 1
75    next_pc = 0
76    next_fp = 0
77    if target.triple[0:6] == "x86_64" or target.triple[0:4] == "i386" or target.triple[0:3] == "arm":
78      error = lldb.SBError()
79      next_pc = process.ReadPointerFromMemory(cur_fp + process.GetAddressByteSize(), error)
80      if not error.Success():
81        next_pc = 0
82      next_fp = process.ReadPointerFromMemory(cur_fp, error)
83      if not error.Success():
84        next_fp = 0
85    # Clear the 0th bit for arm frames - this indicates it is a thumb frame
86    if target.triple[0:3] == "arm" and (next_pc & 1) == 1:
87      next_pc = next_pc & ~1
88    cur_pc = next_pc
89    cur_fp = next_fp
90  backtrace_print_frame (target, frame_num, cur_pc, cur_fp)
91
92def diagnose_unwind(debugger, command, result, dict):
93  """
94Gather diagnostic information to help debug incorrect unwind (backtrace)
95behavior in lldb.  When there is a backtrace that doesn't look
96correct, run this command with the correct thread selected and a
97large amount of diagnostic information will be printed, it is likely
98to be helpful when reporting the problem.
99  """
100
101  command_args = shlex.split(command)
102  parser = create_diagnose_unwind_options()
103  try:
104    (options, args) = parser.parse_args(command_args)
105  except:
106   return
107  target = debugger.GetSelectedTarget()
108  if target:
109    process = target.GetProcess()
110    if process:
111      thread = process.GetSelectedThread()
112      if thread:
113        lldb_versions_match = re.search(r'[lL][lL][dD][bB]-(\d+)([.](\d+))?([.](\d+))?', debugger.GetVersionString())
114        lldb_version = 0
115        lldb_minor = 0
116        if len(lldb_versions_match.groups()) >= 1 and lldb_versions_match.groups()[0]:
117          lldb_major = int(lldb_versions_match.groups()[0])
118        if len(lldb_versions_match.groups()) >= 5 and lldb_versions_match.groups()[4]:
119          lldb_minor = int(lldb_versions_match.groups()[4])
120
121        print 'LLDB version %s' % debugger.GetVersionString()
122        print 'Unwind diagnostics for thread %d' % thread.GetIndexID()
123        print ""
124        print "lldb's unwind algorithm:"
125        print ""
126        frame_num = 0
127        for frame in thread.frames:
128          if not frame.IsInlined():
129            backtrace_print_frame (target, frame_num, frame.GetPC(), frame.GetFP())
130            frame_num = frame_num + 1
131        print ""
132        print "============================================================================================="
133        print ""
134        print "Simple stack walk algorithm:"
135        print ""
136        simple_backtrace(debugger)
137        print ""
138        print "============================================================================================="
139        print ""
140        for frame in thread.frames:
141          if not frame.IsInlined():
142            print "--------------------------------------------------------------------------------------"
143            print ""
144            print "Disassembly of %s, frame %d" % (frame.GetFunctionName(), frame.GetFrameID())
145            print ""
146            if lldb_major > 300 or (lldb_major == 300 and lldb_minor >= 18):
147                if target.triple[0:6] == "x86_64" or target.triple[0:4] == "i386":
148                  debugger.HandleCommand('disassemble -F att -a 0x%x' % frame.GetPC())
149                else:
150                  debugger.HandleCommand('disassemble -a 0x%x' % frame.GetPC())
151            else:
152              debugger.HandleCommand('disassemble -n "%s"' % frame.GetFunctionName())
153        print ""
154        print "============================================================================================="
155        print ""
156        for frame in thread.frames:
157          if not frame.IsInlined():
158            print "--------------------------------------------------------------------------------------"
159            print ""
160            print "Unwind instructions for %s, frame %d" % (frame.GetFunctionName(), frame.GetFrameID())
161            print ""
162            if lldb_major > 300 or (lldb_major == 300 and lldb_minor >= 20):
163              debugger.HandleCommand('image show-unwind -a "0x%x"' % frame.GetPC())
164            else:
165              debugger.HandleCommand('image show-unwind -n "%s"' % frame.GetFunctionName())
166
167def create_diagnose_unwind_options():
168  usage = "usage: %prog"
169  description='''Print diagnostic information about a thread backtrace which will help to debug unwind problems'''
170  parser = optparse.OptionParser(description=description, prog='diagnose_unwind',usage=usage)
171  return parser
172
173lldb.debugger.HandleCommand('command script add -f %s.diagnose_unwind diagnose-unwind' % __name__)
174print 'The "diagnose-unwind" command has been installed, type "help diagnose-unwind" for detailed help.'
175