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# 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
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)
# A simple stack walk algorithm that follows the frame chain after the first two frames.
def simple_backtrace(debugger):
target = debugger.GetSelectedTarget()
process = target.GetProcess()
cur_thread = process.GetSelectedThread()
backtrace_print_frame (target, 0, cur_thread.GetFrameAtIndex(0).GetPC(), cur_thread.GetFrameAtIndex(0).GetFP())
if cur_thread.GetNumFrames() < 2:
return
cur_fp = cur_thread.GetFrameAtIndex(1).GetFP()
cur_pc = cur_thread.GetFrameAtIndex(1).GetPC()
# If the pseudoreg "fp" isn't recognized, on arm hardcode to r7 which is correct for Darwin programs.
if cur_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":
cur_fp = int (reg.GetValue(), 16)
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:
backtrace_print_frame (target, frame_num, cur_pc, cur_fp)
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
backtrace_print_frame (target, frame_num, cur_pc, cur_fp)
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])
print 'LLDB version %s' % debugger.GetVersionString()
print 'Unwind diagnostics for thread %d' % thread.GetIndexID()
print ""
print "lldb's unwind algorithm:"
print ""
frame_num = 0
for frame in thread.frames:
if not frame.IsInlined():
backtrace_print_frame (target, frame_num, frame.GetPC(), frame.GetFP())
frame_num = frame_num + 1
print ""
print "============================================================================================="
print ""
print "Simple stack walk algorithm:"
print ""
simple_backtrace(debugger)
print ""
print "============================================================================================="
print ""
for frame in thread.frames:
if not frame.IsInlined():
print "--------------------------------------------------------------------------------------"
print ""
print "Disassembly of %s, frame %d" % (frame.GetFunctionName(), frame.GetFrameID())
print ""
if lldb_major > 300 or (lldb_major == 300 and lldb_minor >= 18):
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())
else:
debugger.HandleCommand('disassemble -n "%s"' % frame.GetFunctionName())
print ""
print "============================================================================================="
print ""
for frame in thread.frames:
if not frame.IsInlined():
print "--------------------------------------------------------------------------------------"
print ""
print "Unwind instructions for %s, frame %d" % (frame.GetFunctionName(), frame.GetFrameID())
print ""
if lldb_major > 300 or (lldb_major == 300 and lldb_minor >= 20):
debugger.HandleCommand('image show-unwind -a "0x%x"' % frame.GetPC())
else:
debugger.HandleCommand('image show-unwind -n "%s"' % frame.GetFunctionName())
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.'
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