[Lldb-commits] [lldb] r180077 - Add a new python file to help diagnose backtrace failures in the field.
Jason Molenda
jmolenda at apple.com
Mon Apr 22 20:40:32 PDT 2013
Author: jmolenda
Date: Mon Apr 22 22:40:32 2013
New Revision: 180077
URL: http://llvm.org/viewvc/llvm-project?rev=180077&view=rev
Log:
Add a new python file to help diagnose backtrace failures in the field.
It will be installed in the LLDB.framework and can be loaded with
(lldb) script import lldb.macosx
after which a "unwind-diagnose" command will be registered. Select
the thread which has a bad backtrace and run this command -- a lot
of information about the stack frames, and an alternate backtrace
algorithm, will be used. The information will often be sufficient
for a remote person to figure out why the backtrace failed.
<rdar://problem/13679300>
Added:
lldb/trunk/examples/python/unwind_diagnose.py
Added: lldb/trunk/examples/python/unwind_diagnose.py
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/examples/python/unwind_diagnose.py?rev=180077&view=auto
==============================================================================
--- lldb/trunk/examples/python/unwind_diagnose.py (added)
+++ lldb/trunk/examples/python/unwind_diagnose.py Mon Apr 22 22:40:32 2013
@@ -0,0 +1,197 @@
+#!/usr/bin/python
+
+# This implements the unwind-diagnose command, usually installed in the debug session like
+# script import lldb.macosx
+# 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 commands
+import optparse
+import os
+import platform
+import re
+import shlex
+import sys
+
+try:
+ # Just try for LLDB in case PYTHONPATH is already correctly setup
+ import lldb
+except ImportError:
+ lldb_python_dirs = list()
+ # lldb is not in the PYTHONPATH, try some defaults for the current platform
+ platform_system = platform.system()
+ if platform_system == 'Darwin':
+ # On Darwin, try the currently selected Xcode directory
+ xcode_dir = commands.getoutput("xcode-select --print-path")
+ if xcode_dir:
+ lldb_python_dirs.append(os.path.realpath(xcode_dir + '/../SharedFrameworks/LLDB.framework/Resources/Python'))
+ lldb_python_dirs.append(xcode_dir + '/Library/PrivateFrameworks/LLDB.framework/Resources/Python')
+ lldb_python_dirs.append('/System/Library/PrivateFrameworks/LLDB.framework/Resources/Python')
+ success = False
+ for lldb_python_dir in lldb_python_dirs:
+ if os.path.exists(lldb_python_dir):
+ if not (sys.path.__contains__(lldb_python_dir)):
+ sys.path.append(lldb_python_dir)
+ try:
+ import lldb
+ except ImportError:
+ pass
+ else:
+ print 'imported lldb from: "%s"' % (lldb_python_dir)
+ success = True
+ break
+ if not success:
+ print "error: couldn't locate the 'lldb' module, please set PYTHONPATH correctly"
+ sys.exit(1)
+
+# 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
+ if frame_num > 0:
+ addr = addr - 1
+
+ sbaddr = lldb.SBAddress()
+ 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)
+
+ addr_width = process.GetAddressByteSize() * 2
+ 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 unwind_diagnose(debugger, command, result, dict):
+ # Use the Shell Lexer to properly parse up command options just like a
+ # shell would
+ command_args = shlex.split(command)
+ parser = create_unwind_diagnose_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'lldb-(\d+)([.](\d+))?([.](\d+))?', debugger.GetVersionString())
+ lldb_version = 0
+ lldb_minor = 0
+ if len(lldb_versions_match.groups()) >= 1:
+ lldb_major = lldb_versions_match.groups(1)
+ if len(lldb_versions_match.groups()) >= 5:
+ lldb_minor = lldb_versions_match.groups(5)
+
+ 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 ""
+ debugger.HandleCommand('image show-unwind -n "%s"' % frame.GetFunctionName())
+
+def create_unwind_diagnose_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='unwind_diagnose',usage=usage)
+ return parser
+
+if __name__ == '__main__':
+ print 'This is not meant to be run from the command line, import it into lldb with a command like "script import lldb.macosx"'
+elif getattr(lldb, 'debugger', None):
+ lldb.debugger.HandleCommand('command script add -f lldb.macosx.unwind_diagnose.unwind_diagnose unwind-diagnose')
+ print 'The "unwind-diagnose" command has been installed, type "help unwind-diagnose" for detailed help.'
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